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FRONTISPIECE.

PLATE I.

TEA PLANT.

FOOD
ADULTERATION
AND
ITS DETECTION.

WITH PHOTOMICROGRAPHIC PLATES AND
A BIBLIOGRAPHICAL APPENDIX.

BY
JESSE P. BATTERSHALL, Ph.D., F.C.S.,
CHEMIST, U.S. LABORATORY,
NEW YORK CITY.

NEW YORK:
E. & F. N. SPON, 35, MURRAY STREET,
AND 125, STRAND, LONDON.
1887.

[Copyright, 1887. By Jesse P. Battershall.]

PREFACE.

To embody in a condensed form some salient features of the present status of Food Adulteration in the United States is the object of this volume. The importance of the subject, and the apparent need of a book of moderate dimensions relating thereto, must suffice as its raison d’être. The standard works have been freely consulted, and valuable data have been obtained from the recent reports of our State and Civic Boards of Health. The system of nomenclature accepted by the American Chemical Society has been generally adopted. It was, however, deemed advisable to retain such names as glycerine, sodium bicarbonate, etc., in place of the more modern but less well-known terms, glycerol and sodium hydrogen carbonate, even at a slight sacrifice of uniformity.

The photogravure plates, most of which represent the results of recent microscopical investigation, are considered an important feature of the book. And it is believed that the bibliographical appendix, and the collation of American Legislation on Adulteration, will supply a want for ready reference often experienced.

U. S. Laboratory,
July 1st, 1887.

CONTENTS.

PLATES.

FOOD ADULTERATION.

INTRODUCTION.

Of the various branches cognate to chemical research which excite public attention, that of food adulteration doubtless possesses the greatest interest. To the dealer in alimentary substances, the significance of their sophistication is frequently merely one of profit or loss, and even this comparatively unimportant consideration does not always attach. But to the general community, the subject appeals to interests more vital than a desire to avoid pecuniary damage, and involving, as it necessarily does, the question of health, it has engendered a feeling of uneasiness, accompanied by an earnest desire for trustworthy information and data. The most usual excuses advanced by dishonest traders, when a case of adulteration has been successfully brought home to them—guilty knowledge being also established—are, that they are compelled to resort to the misdeed by the public demand for cheap commodities, that the addition is harmless, or actually constitutes an improvement, as is asserted to be the case when chicory is added to coffee, or that it serves as a preservative, as was formerly alleged to be the fact when vinegar was fortified with sulphuric acid. Pretexts of this sort are almost invariably fallacious. The claim that manufacturers are often forced into adulteration by the necessities of unfair trade competition possesses more weight—an honest dealer cannot as a rule successfully compete with a dishonest one—and has undoubtedly influenced many of the better class to co-operate in attempts to prevent the practice. The general feeling of uncertainty which exists in the public mind concerning the actual extent and importance of food adulteration is probably to be ascribed to two causes. In the first place, most of the literature generally accessible relating to the subject has been limited to sensational newspaper articles, reciting some startling instance of food-poisoning, often unauthenticated and bearing upon its face evidences of exaggeration. By reason of such publications, periodical panics have been created in our large cities which, however, as a rule quickly subside, and the community relapses into the customary feeling of doubtful security, until aroused from its apathy by the next exposé. The fact that the only reliable results of food investigation have, until recently, been confined to purely scientific journals, and therefore not prominently brought to public notice, is another explanation of the lack of creditable information which generally prevails concerning this species of sophistication.

The adulteration of alimentary substances was practised in the civilised countries of Europe at a very remote date, and the early history of the art, mainly collated by Prof. Blyth in his valuable work on food,[1] is replete with interest. Bread certainly received due attention at the hands of the ancient sophisticator. Pliny makes several references to the adulteration of this food. In England, as early as the reign of King John, the sale of the commodity was controlled by the “Assize of Bread,” which, although originally designed to regulate the price and size of the loaf, was subsequently amplified so as to include penalties for falsification, usually consisting of corporal punishment and exposure in the pillory. In France, in 1382, ordinances were promulgated specifying the proper mode of bread-making, the punishment for infringement being similar in character to those inflicted in Great Britain. It is related that in the year 1525, a guilty baker “was condemned by the court to be taken from the Châtelet prison to the cross before the Église des Carmes, and thence to the gate of Notre Dame and to other public places in Paris, in his shirt, having his head and feet bare, with small loaves hung from his neck, and holding a large wax candle, lighted, and in each of the places enumerated he was to make amende honorable, and ask mercy and pardon of God, the king, and of justice for his fault.” In Germany, during the fifteenth century, the bread adulterator, while not subjected to a religious penance, did not escape from a sufficiently practical rebuke, as it was the frequent custom to put him in a basket attached to a long pole, and purge him of his misdeeds by repeated immersions in a pool of water.

Wine would also appear to have been exposed to fraudulent admixture in former times. Pliny mentions that in Rome considerable difficulty was experienced, even by the wealthy, in securing the pure article, and in Athens a public inspector was early appointed to prevent its adulteration. In England, during the reign of Edward the Confessor, punishment for brewing bad beer was publicly enforced, and, in 1529, official “ale tasters” flourished, without whose approval the beverage was not to be sold. In later years, Addison, referring to the manipulators of wine of his time, writes: “These subtle philosophers are daily employed in the transmutation of liquors, and, by the power of magical drugs and incantations, raise under the streets of London the choicest products of the hills and valleys of France; they squeeze Bordeaux out of the sloe and draw champagne from an apple.”[2] In the fifteenth century, at Biebrich on the Rhine, a wine sophisticator was forced to drink six quarts of his own stock, and it is recorded with due gravity that the test resulted fatally. Not very many years since, a manufacturer of wine at Rheims secured for his champagne, which was chiefly consumed in Würtemberg, a high reputation, on account of the unusually exhilarating effects following its use. Suspicion being at length aroused, Liebig made a chemical examination of the article, and found that it was at least unique in its gaseous composition, being charged with one volume of carbonic acid gas and two volumes of nitrous oxide, or “laughing gas.” These early attempts to control and punish adulteration, while often possessing interest on account of their quaintness, are chiefly important, as being the precursors of the protective legal measures which exist in more modern times.

In 1802 the Conseil de Salubrité was established in Paris, and this body has since developed into numerous health boards, to whom the French are at present mainly indebted for what immunity from food falsification they enjoy. A very decided advance upon all preceding methods to regulate the public supply of food was signalised in 1874 by the organisation in England of the Society of Public Analysts, who formulated a legal definition of adulteration, and issued the standards of purity which articles of general consumption should meet. This society was supported in its valuable services by the enactment, in 1875, of the Sale of Food and Drugs Act, which, with the amendment added in 1879, seems to embrace all necessary safeguards against the offences sought to be suppressed. The results of their work are tabulated as follows:—

Of the total number of samples tested, the classification of adulterations is as below:—

More recent data concerning the falsification of food in Great Britain are as follows:—

Of the samples of spirits and beer examined, about 25 per cent. were adulterated.

The results of the work done at the Paris Municipal Laboratory are the following:—

The American characteristic of controlling their own personal affairs, and the resulting disinclination to resort to anything savouring of parental governmental interference, has probably had its effect in retarding early systematic action in the matter of adulteration. Sporadic attempts to secure legislative restrictions have, it is true, occasionally been made, but the laws passed were almost invariably of a specific nature, designed to meet some isolated case, and were destined to share the fate of most legislation of the kind—the particular adulteration being for the nonce suppressed, the law became practically a dead letter. Subsequent effort to obtain more comprehensive laws inclined to the other extreme, and the enactments secured were so general in scope, and so deficient in details, that loopholes were inadvertently allowed to remain, through which the crafty adulterator often managed to escape.

The present food legislation in the United States was to some extent anticipated in 1848 by an Act of Congress to secure the purity of imported drugs. In this enactment these are directed to be tested by the standards established by the various official pharmacopœias; twenty-three are specifically enumerated, the most important being Peruvian bark and opium. The Act is still in force. All previous efforts to regulate the quality of our food supply culminated in 1877 in formal action being taken by several of the State Boards of Health, at whose instance laws against adulteration were formulated, and chemists commissioned to collect and examine samples of alimentary substances, and furnish reports on the subject. These may be found in the publications of the same, notably in the volumes issued by the New York, Massachusetts, Michigan, and New Jersey Boards. The service rendered to the public by these investigations is almost incalculable, and the annual reports containing the results of the same are fraught with interest. For the first time we are placed in possession of trustworthy statistics, indicating the extent of food sophistication in this country.

The annual report of the New York City Board of Health for the year 1885 furnishes the following statistics:—

Some of the results of the work performed by the New York State Board of Health during the year 1882 are tabulated below:—

In interpreting the significance of the foregoing table, it should be borne in mind that in the vast majority of cases the adulterations practised were not of an injurious nature, but consisted of a fraudulent admixture of some cheaper substance, the object being an increase of bulk or weight resulting in augmented profit.

Much of the embarrassment experienced by health authorities in their efforts to bring persons guilty of food adulteration to punishment is due to the lack of explicit detail in the law. It is far easier to substantiate the fact of the adulteration than it is to produce the offender in court and secure his conviction. Numerous cases are on record illustrating the peculiar contingencies which at times arise. Probably with the best intention, a milk vendor labelled his wagon, “Country skimmed milk, sold as adulterated;” an inspector bought a sample, not noticing the label, and the magistrate convicted the vendor, doubtless on the ground that due attention had not been directed to the advertisement.[3] Chief Justice Cockburn, in referring to an analogous case, said: “If the seller chooses to sell an article with a certain admixture, the onus lies on him to prove that the purchaser knew what he was purchasing.” In most instances, when in ostensible compliance with the law, a package bears a label purporting to state the actual nature of its contents, the label is either printed in such small type, or is placed in so inconspicuous a position, that the buyer is in ignorance of its existence at the time the purchase is made. A confectioner in Boston was suspected of selling adulterated candy, and while it was proved that a sample bought of him contained a dangerous proportion of a poisonous pigment—chromate of lead—he escaped conviction, on the plea that candy was not an article of food within the meaning of the existing law, which, it seems, has since been amended so as to embrace cases of this kind.

In a recent action brought by the New York Board of Health to obtain an injunction against the sale of certain Ping Suey teas, it was held by the court, in refusing to grant the same, that, although the teas in question had been clearly shown to be adulterated with gypsum, Prussian blue, sand, etc., it was likewise necessary to prove that the effect of these admixtures was such as to constitute a serious danger to public health.

As a result of the publicity lately given to the subject of food adulteration, a popular impression has been produced that any substance employed as an adulterant of, or a substitute for another, is to be avoided per se. Perhaps the common belief that for all purposes cotton-seed oil is inferior to olive oil, and oleomargarine to butter, is the most striking illustration of this tendency. Now, as a matter of fact, pure cotton-seed oil, as at present found on the market, is less liable to become rancid than the product of the olive, and, for many culinary uses, it is at least quite as serviceable. Absolute cleanliness is a sine qua non in the successful manufacture of oleomargarine, and, as an economical substitute for the inferior kinds of butter often exposed for sale, its discovery cannot justly be regarded a misfortune. The sale of these products, under their true name, should not only be allowed, but under some circumstances even encouraged.

The benefits accruing to the community by reason of the service of our State Boards of Health are so evident and so important, that it is almost incredible that these bodies have not been put in possession of all the facilities necessary for their work. It would appear, however, that, while our legislators have been induced to enact good laws regulating adulteration, they have often signally failed to fulfil all the requirements indispensable to the efficient execution of the same. Without entering into the details of this branch of the subject, it is proper to observe that owing to the lack of necessary funds, great pecuniary embarrassment has been experienced in securing the services of a competent corps of experts, who, in addition to their inadequate remuneration, must incur the expenses of purchasing samples. The appointment of public analysts in our larger towns and cities—as has for some time been the case in Great Britain—is certainly to be urgently recommended.

All attempts to awaken public interest in the subject of food adulteration are of any real service only as they may be conducive to the adoption of more advanced and improved measures for the suppression of the practice.

In general, the adulterations to which food is subjected may be divided into those positively deleterious to health (such as the colouring of confectionery by chrome yellow), those which are only fraudulent (such as the addition of flour to mustard), and those which may be fairly considered as accidental (such as the presence of a small amount of sand in tea). It would exceed the limits of this volume to enter into a comprehensive review of the almost endless varieties of adulteration. The following list embraces the articles most exposed to falsification, together with the adulterants commonly employed:—

The above table includes those admixtures which have actually been detected by chemists of repute within the past few years, and omits many rather sensational forms of adulteration mentioned in the early treatises on the subject, the practice of which appears to have been discontinued.

In the following pages, some of the more important articles of food and drink are described with especial reference to their chemical relations and the ordinary adulterations to which they are exposed. It should be added, that many of the methods of examination given are quoted in a condensed form from the more extensive works on food-analysis.

TEA.

The early history of tea is probably contemporary with that of China, although, in that country, the first authentic mention of the plant was as late as A.D. 350; while, in European literature, its earliest notice occurs in the year 1550. The first important consignment of tea into England took place in 1657. Chinese tea made its appearance in the United States in 1711; in 1858, the importation of Japan tea began. During the season of 1883-1884, the importation of tea into this country[4] was—from China, 30½ millions of pounds; from Japan, 32½ millions of pounds. Recently, numerous shipments of Indian tea have been placed upon our markets, the quality of which compares very favourably with the older and better known varieties. During the past four years the consumption of tea in this country has materially decreased; whilst that of coffee has undergone an almost corresponding increase. The per capita consumption of tea and coffee in the United States as compared with that of Great Britain is as follows:—United States, tea, 1·16; coffee, 9·50; Great Britain, tea, 4·62; coffee, 0·89. In the year 1885 our importation of tea approximated 82 millions of pounds, that of coffee being nearly 455 millions of pounds.

Genuine tea is the prepared leaf of Thea sinensis. The growth of the tea shrub is usually restricted by artificial means to a height of from three to five feet. It is ready for picking at the end of the third year, the average life of the plant being about ten years. The first picking is made in the middle of April, the second on the 1st of May, the third in the middle of July, and occasionally a fourth during the month of August. The first pickings, which obviously consist of the young and more tender leaves, furnish the finer grades of tea. After sorting, the natural moisture of the leaves is partially removed by pressing and rolling; they are next more thoroughly dried by gently roasting in iron pans for a few minutes. The leaves are then rolled on bamboo tables and again roasted, occasionally re-rolled and re-fired, and finally separated into the various kinds, such as twankay, hyson, young hyson, gunpowder, etc., by passing through sieves. The difference between green and black tea is mainly due to the fact that the former is dried shortly after gathering, and then rolled and carefully fired, whereas black tea is first made up into heaps, which are exposed to the air for some time before firing and allowed to undergo a species of fermentation, resulting in the conversion of its original olive-green into a black colour. The methods employed in the preparation of the tea are somewhat modified in their details in the different tea districts of China and Japan. In Japan two varieties of the leaf are used, which are termed “otoko” (male), and “ona” (female), the former being larger and coarser than the latter. After picking, the leaves are steamed by placing them in a wooden tray suspended over boiling water, in which they are allowed to remain for about half a minute. They are next thrown upon a tough paper membrane attached to the top of an oven, which is heated by burning charcoal covered with ashes, where they are constantly manipulated by the hand until the light-green colour turns to a dark olive, and the leaves have become spirally twisted. After this “firing,” the tea is dried at a low temperature for from four to eight hours; it is next sorted by passing through sieves, and is then turned over to the “go-downs,” or warehouses of the foreigners, where the facing process is carried on by placing the tea in large metallic bowls, heated by means of a furnace, and gradually adding the various pigments used, the mixture being continually stirred. The tea is finally again sorted by means of large fans, and is now ready for packing and shipment.

The sophistications to which tea is exposed have received the careful attention of chemists, but not to a greater extent than the importance of the subject merits; indeed, it is safe to assert that no article among alimentary substances has been, at least in past years, more subjected to adulteration. The falsifications which are practised to no inconsiderable extent may be conveniently divided into three classes.

1st. Additions made for the purpose of giving increased weight and bulk, which include foreign leaves and spent tea leaves, and also certain mineral substances, such as metallic iron, sand, brick-dust, etc.

2nd. Substances added in order to produce an artificial appearance of strength to the tea decoction, catechu and other bodies rich in tannin being mainly resorted to for this purpose.

3rd. The imparting of a bright and shining appearance to an inferior tea by means of various colouring mixtures or “facings,” which operation, while sometimes practised upon black tea, is far more common with the green variety. This adulteration involves the use of soap-stone, gypsum, China clay, Prussian blue, indigo, turmeric, and graphite. The author lately received from Japan several samples of the preparations employed for facing the tea in that country, the composition of which was shown by analysis to be essentially as follows:—

1. Magnesium silicate (soap-stone).
2. Calcium sulphate (gypsum).
3. Turmeric.
4. Indigo.
5. Ferric ferrocyanide (Prussian blue).
6. Soap-stone, 47·5 per cent.; gypsum, 47·5 per cent.; Prussian blue, 5 per cent.
7. Soap-stone, 45 per cent.; gypsum, 45 per cent.; Prussian blue, 10 per cent.
8. Soap-stone, 75 per cent.; indigo, 25 per cent.
9. Soap-stone, 60 per cent.; indigo, 40 per cent.

The “facing” or “blooming” of tea is often accomplished by simply placing it in an iron pan, heated by a fire, and rapidly incorporating with it one of the preceding mixtures (Nos. 6, 7, 8, or 9), in the proportion of about half a dram to seven or eight pounds of the tea, a brisk stirring being maintained until the desired shade of colour is produced.

Some of the above forms of sophistication usually go together;—thus exhausted tea is restored by facing. The collection of the spent leaves takes place in China. Much of the facing was, until about three years since, done in New York city, and constituted a regular branch of business, which included among its operations such metamorphoses as the conversion of a green tea into a black, and vice versâ.

According to James Bell,[5] the composition of genuine tea is as follows:—

The ash of samples of uncoloured and unfaced tea, and of spent tea analysed by the author, had the following composition:—

Composition.

“Tea dust” affords a high proportion of ash, sometimes amounting to 20 per cent., the composition of which is usually strikingly different from that of the ash of ordinary tea. It is deficient in potassa and phosphoric acid, and the amount of ash insoluble in water and acids is very excessive, as is shown by the following analysis, made by the author:—

Ash of Tea Dust.

PLATE II.

TEA LEAVES.

The portion of ash insoluble in acids consisted of silica, clay, and soapstone, indicating that the ash of tea dust is largely composed of the mineral substances employed for “facing” purposes.

The characteristics of the ash of unspent tea are the presence of manganic oxide, the large proportion of potassium salts present, and the solubility of the ash in water. The amount of ash in genuine tea ranges from five to six per cent. In the absence of exhausted leaves, it has been found that the finer sorts of tea afford a smaller proportion of ash than the inferior grades. It will be noticed that spent tea ash exhibits a marked increase in the proportion of insoluble compounds (silica, alumina, and ferric oxide), as well as a total absence of potassium salts.

The presence of foreign leaves, and, in some instances, of mineral adulterants in tea is best detected by means of a microscopical examination of the suspected sample. The genuine tea-leaf is characterised by its peculiar serrations and venations. Its border exhibits serrations which stop a little short of the stalk, while the venations extend from the central rib, nearly parallel to one another, but turn just before reaching the border of the leaf.

Plate I. (Frontispiece) is a photogravure of a twig of the tea plant, in possession of the author. The leaves are of natural size, but the majority are of a greater maturity than those used in the preparation of tea, which more resemble in size the few upper leaves.

Plate II. shows more distinctly the serrations and venations of the tea-leaf. The Chinese are said to occasionally employ ash, camelia, and dog-rose leaves for admixture with tea, and the product is stated to have formerly been subjected in England to the addition of sloe, willow, beech, hawthorn, oak, etc. For scenting purposes, chulan flowers, rose, jasmine, and orange leaves, have been employed. The writer has lately received from Japan specimens of willow, wisteria, te-mo-ki, and other leaves which at one time were used in that country as admixtures.

Plate III. exhibits some of these leaves, two genuine Japan tea-leaves being included for purpose of comparison. The leaves represented in this plate are: 1, beech; 2, hawthorn; 3, rose; 4, Japan tea; 5, willow; 6, te-mo-ki; 7, elm; 8, wisteria; 9, poplar. From very recent reports of the American consuls in Japan and China, it would appear that the addition of foreign leaves to tea is at present but seldom resorted to, and this accords with the author’s experience in the testing of the teas imported into this country.

In 1884, the Japanese Government made it a criminal offence to adulterate tea, and instituted “tea guilds,” which are governed by very stringent laws, and of which most dealers of repute are members. The facing of tea does not appear, however, to have been considered an adulteration, its continued practice being justified by the plea that otherwise Japan teas would not suit the taste of American consumers.

PLATE III.

TEA AND OTHER LEAVES.

In the microscopic examination of tea, the sample should be moistened with hot water and spread out on a glass plate, and then submitted to a careful inspection, especial attention being directed to the general outline of the leaf and its serrations and venations. The presence of exhausted tea-leaves may often be detected by their soft texture and generally disintegrated appearance. If a considerable quantity of the tea be placed in a long glass cylinder and agitated with cold water, the colouring and other abnormal substances frequently become detached, and either rise to the surface of the liquid as a sort of scum, or fall to the bottom as a sediment. In this way Prussian blue, indigo, soapstone, gypsum, sand, and turmeric can often be separated, and subsequently recognised by their characteristic appearance under the microscope. The separated substances should also be subjected to a chemical examination. Prussian blue is detected by heating with a solution of sodium hydroxide, filtering, acidulating the filtrate with acetic acid, and then adding ferric chloride, when, in its presence, a blue colour will be produced. Indigo is best recognised by the microscopic examination. It is not decolorised by caustic alkali, but it dissolves in sulphuric acid to a blue liquid. Soapstone, gypsum, sand, and metallic iron, are identified by means of the usual chemical reactions. A compound very aptly termed “Lie-tea,” is sometimes met with. It forms little pellets, consisting of tea-dust mixed with foreign leaves, sand, etc., and held together by means of gum or starch. This falls to powder if treated with boiling water. In the presence of catechu, the tea infusion usually assumes a muddy appearance upon standing. In case iron salts have been employed to deepen the colour of the infusion, they can be detected by treating the ground tea-leaves with acetic acid, and testing the filtered solution with potassium ferrocyanide. Tea should not turn black upon immersion in hydrosulphuric acid water, nor should it impart a blue colour to ammonia water. The infusion should be amber-coloured, and not become reddened by the addition of an acid.

The United States Tea Adulteration Act was passed by Congress in 1883. The enactment of this law was largely due to the exertions of prominent tea merchants, whose business interests were seriously affected by the sale (principally in trade auctions) of the debased or spurious article. It is stated in the official report of the United States Tea Examiner at New York City, that from March 1883 to December of the same year, 856,281 packages (about four millions of pounds) of tea were inspected, of which 7000 packages (325,000 pounds) were rejected as unfit for consumption. Since the enforcement in New York City of the Tea Adulteration Act, nearly 2000 samples of tea have been chemically tested under the direction of the author. The proportion grossly adulterated has been a little over nine per cent. But this does not apply to the total amount imported, since only those samples which were somewhat suspicious in appearance were submitted for analysis. As the result of the past two years’ experience in the chemical examination of tea, the prevailing adulterations were found to be of two kinds—the admixture of spent tea-leaves, and the application to the tea of a facing preparation. A natural green tea possesses a dull hue, and is but seldom met with in the trade; some Moyunes and uncoloured Japans (which latter, properly speaking, is not a green tea) being almost the only varieties not exhibiting the bright metallic lustre due to the facing process. The addition of foreign leaves was detected only in a few instances; the presence of sand and gravel occurred far more frequently. Apropos of the practical utility of Governmental sanitary legislation, it can be stated that, since the enforcement of the Adulteration Act, the tea imported into the city of New York has very perceptibly improved in quality.

Attempts in tea culture are being made in the United States of Columbia, S.A. A specimen of the prepared plant received by the writer, differed greatly in appearance from the Chinese and Japanese products. The leaves, which had not been rolled but were quite flat, possessed a light pea-green colour and a fine but rather faint aroma. An examination indicated that the tea, although very delicate in quality, was seriously deficient in body.

The analysis showed:—

The following Tea Assay, while not including the determinations of all the proximate constituents of the plant, will, it is believed, in most instances suffice to indicate to the analyst the presence of spent leaves, mineral colouring matters, and other inorganic adulterations.

Theine (Caffeine), C8H10N4O2.—Contrary to the once general belief, there does not always exist a direct relation between the quality of tea (at least so far as this is indicated by its market price) and the proportion of theine contained, although the physiological value of the plant is doubtless due to the presence of this alkaloid.

The commercial tea-taster is almost entirely guided in his judgment in regard to the value of a sample of tea by the age of the leaf, and by the flavour or bouquet produced upon “drawing,” and this latter quality is to be mainly ascribed to the volatile oil.

The following process will serve for the estimation of theine:—A weighed quantity of the tea is boiled with distilled water until the filtered infusion ceases to exhibit any colour. The filtrate is evaporated on a water bath to the consistence of a syrup; it is next mixed with calcined magnesia to alkaline reaction, and carefully evaporated to dryness.

The residue obtained is then finely powdered, digested for a day or so with ether (or chloroform) and filtered, the remaining undissolved matter being again digested with a fresh quantity of ether, so long as any further solution of theine takes place. The ether is now removed from the united filtrates by distillation, whereupon the theine will be obtained in a fairly pure condition.

Theine contains a very large proportion of nitrogen (almost 29 per cent.), and Wanklyn[6] has suggested the application of his ammonia process (see p. [205]) to the analysis of tea. Genuine tea is stated to yield from 0·7 to 0·8 per cent. of total ammonia, when tested in this manner.

Volatile Oil.—Ten grammes of the tea are distilled with water; the distillate is filtered, saturated with calcium chloride, then well agitated with ether, and allowed to remain at rest for some time. The ethereal solution is subsequently drawn off, and spontaneously evaporated in a weighed capsule. The increase in weight gives approximately the amount of oil present. A sample of good black tea yielded by this method 0·87 per cent. of volatile oil.

Tannin.—Two grammes of the well-averaged sample are boiled with 100 c.c. of water, for about an hour, and the infusion filtered, the undissolved matter remaining upon the filter being thoroughly washed with hot water, and the washings added to the solution first obtained. If necessary, the liquid is next reduced to a volume of 100 c.c. by evaporation over a water-bath. It is then heated to boiling, and 25 c.c. of a solution of cupric acetate added. The copper solution is prepared by dissolving five grammes of the salt in 100 c.c. of water, and filtering. The precipitate formed is separated by filtration, well washed, dried, and ignited in a porcelain crucible. A little nitric acid is then added and the ignition repeated. One gramme of the cupric oxide thus obtained represents 1·305 grammes of tannin. For the estimation of spent leaves (especially in black tea), Mr. Allen suggests the following formula, in which E represents the percentage of spent tea, and T the percentage of tannin found:—

E = (10 - T) 100 8.

The Ash.—a. Total Ash.—Five grammes of the sample are placed in a platinum dish and ignited over a Bunsen burner until complete incineration is accomplished. The vessel is allowed to cool in a desiccator, and is then quickly weighed. In genuine tea the total ash should not be much below 5 per cent., nor much above 6 per cent., and it should not be magnetic. In faced teas the proportion of total ash is sometimes 10 per cent.; in “lie-tea” it may reach 30 per cent.; while in spent tea it frequently falls below 3 per cent., the ash in this case being abnormally rich in lime salts, and poor in potassium salts.

b. Ash insoluble in water.—The total ash obtained in a is washed into a beaker, and boiled with water for a considerable time. It is then brought upon a filter, washed, dried, ignited, and weighed. In unadulterated tea it rarely exceeds 3 per cent. of the sample taken.

c. Ash soluble in water.—This proportion is obtained by deducting the ash insoluble in water from the total ash. Genuine tea contains from 3 per cent. to 3·5 per cent. of soluble ash, or at least 50 per cent. of the total ash, whereas in exhausted tea the amount is often but 0·5 per cent. The following formula has been proposed for the calculation of the percentage of spent tea E, where S is the percentage of soluble ash obtained:—

E = (6 - 2S) 20.

A sample prepared by averaging several good grades of black tea, was mixed with an equal quantity of exhausted tea-leaves. The proportion of soluble ash in the mixture was found to be 1·8 per cent. According to the above formula, the spent tea present would be 48 per cent., or within 2 per cent. of the actual amount.

d. Ash insoluble in acid.—The ash insoluble in water is boiled with dilute hydrochloric acid, and the residue separated by filtration, washed, ignited, and weighed. In pure tea, the remaining ash ranges between 0·3 and 0·8 per cent.; in faced tea, or in tea adulterated by the addition of sand, etc., it may reach the proportion of 2 to 5 per cent. Fragments of silica and brickdust are occasionally found in the ash insoluble in acid.

The Extract.—Two grammes of the carefully sampled tea are boiled with water until all soluble matter is dissolved, more water being added from time to time to prevent the solution becoming too concentrated. The operation may also be conducted in a flask connected with an ascending Liebig’s condenser. In either case, the infusion obtained is poured upon a tared filter, and the remaining insoluble leaf repeatedly washed with hot water so long as the filtered liquor shows a colour. The filtrate is now diluted to a volume of 200 c.c., and of this 50 c.c. are taken and evaporated in a weighed dish until the weight of the extract remains constant. Genuine tea affords from 32 to 50 per cent. of extract, according to its age and quality; in spent tea the proportion of extract will naturally be greatly reduced. Mr. Allen employs the formula below for determining the percentage of spent tea E in a sample, R representing the percentage of extract found.

E = (32 - R) 100 30.

In order to test the practical value of this equation, a sample of black tea was mixed with 50 per cent. of spent tea-leaves, and a determination made of the extract afforded. The calculated proportion of spent tea was 44 per cent., instead of 50 per cent. It should be added, however, that the tea taken subsequently proved to be of a very superior quality, yielding an extract of 40 per cent.

Gum (Dextrine).—The proportion of gum contained in genuine tea is usually inconsiderable. Its separation is effected by treating the concentrated extract with alcohol, allowing the mixture to stand at rest for a few hours, and collecting the precipitated gum upon a tared filter, and carefully drying and weighing it. As a certain amount of mineral matter is generally present in the precipitate, this should afterwards be incinerated and a deduction made for the ash thus obtained. A more satisfactory method is to treat the separated dextrine with very dilute sulphuric acid, and estimate the amount of glucose formed by means of Fehling’s solution (see p. [37]); 100 parts of glucose are equivalent to 90 parts of dextrine.

Insoluble Leaf.—The insoluble leaf as obtained in the determination of the extract, together with the weighed filter, is placed in an air-bath, and dried for at least eight hours at a temperature of 100°,[7] and then weighed. In genuine tea the amount of insoluble leaf ranges from 47 to 54 per cent.; in exhausted tea it may reach a proportion of 75 per cent. or more. It should be noted that in the foregoing estimations the tea is taken in its ordinary air-dried condition. If it be desired to reduce the results obtained to a dry basis, an allowance for the moisture present in the sample (an average of 6 to 8 per cent.), or a direct determination of the same must be made.

The following tabulation gives the constituents of genuine tea, so far as the ash, extract, and insoluble leaf are involved:—

Total ash ranges between 4·7 and 6·2 per cent.

Ash soluble in water ranges between 3 and 3·5 per cent.; should equal 50 per cent. of total ash.

Ash insoluble in water, not over 3 per cent.

Ash insoluble in acid ranges between 0·3 and 0·8 per cent.

Extract[8] ranges between 32 and 50 per cent.

Insoluble leaf ranges between 43 and 58 per cent.

The table below may prove useful as indicating the requirements to be exacted when the chemist is asked to give an opinion concerning the presence of facing admixtures, or of exhausted or foreign leaves in a sample of tea.

Total ash should not be under 4·5 per cent. or above 7 per cent.

Ash soluble in water should not be under 40 per cent. of total ash.

Ash insoluble in water should not be over 3·25 per cent.

Ash insoluble in acid should not be over 1 per cent.

Extract (excepting in poor varieties of Congou tea) should not be under 30 per cent.

Insoluble Leaf should not be over 60 per cent.

The British Society of Public Analysts adopt:—

Total ash (dry basis), not over 8 per cent. (at least 3 per cent. should be soluble in water).

Extract (tea as sold), not under 30 per cent.

Below are the proportions of total ash, ash soluble in water, and extract found in 850 samples of tea (mostly inferior and faced), examined under the direction of the author in the U.S. Laboratory:—

Total Ash.

Ash Soluble in Water.

Extract.

The following tabulation exhibits the results obtained by the examination of various grades of Formosa, Congou, Young Hyson, Gunpowder, and Japan tea, made, under the supervision of the writer, by Dr. J. F. Davis.

It will be noticed, if the same varieties of tea be compared, that, with some exceptions, their commercial value is directly proportional to the percentages of soluble ash, extract, tannin, and theine contained.

The following analyses of several kinds of spurious tea, received from the U.S. Consuls at Canton and Nagasaki (Japan), have been made by the author:—

1. Partially exhausted and refired tea-leaves, known as “Ching Suey” (clear water), which name doubtless has reference to the weakness of a beverage prepared from this article.

2. “Lie tea,” made from Wampan leaves.

3. A mixture of 10 per cent. green tea and 90 per cent. “lie tea.” It is sometimes sold as “Imperial” or “Gunpowder” tea, and is stated to be extensively consumed in France and Spain.

4. “Scented caper tea,” consisting of tea-dust made up into little shot-like pellets by means of “Congou paste” (i. e. boiled rice), and said to be chiefly used in the English coal-mining districts.

The following are the results of the analysis by American chemists of samples representing 2414 packages of Indian tea.

COFFEE.

Coffee is the seed of the Caffea Arabica, indigenous to Abyssinia and southern Arabia, and since naturalised in the West Indies, Ceylon, Brazil, and other tropical countries. Its importance as an almost universal beverage is only equalled by that of tea. The ancient history of coffee is shrouded in great obscurity. It was unknown to the Romans and Greeks, but its use is said to have been prevalent in Abyssinia from the remotest time, and in Arabia it formed an article of general consumption during the fifteenth century. From its introduction, in 1575, into Constantinople by the Turks, it gradually made its way into all civilised countries. In 1690 it was carried by the Dutch from Mocha to Java, whence specimens of the tree were taken to Holland and France. Coffee houses were opened in London about the middle of the seventeenth century, and in 1809 the first cargo of coffee was shipped to the United States. As with many other articles of diet, the adulteration of coffee has kept well apace with its increased consumption. The bean is deprived of its external fleshy coatings before exportation, and is met with in commerce in a raw, roasted, or ground condition. Bell[9] gives the following analyses of two samples of coffee, both in the raw and roasted state:—

Other authorities have obtained the following results:—

It will be noticed from these analyses that the amount of sugar is greatly diminished by the process of roasting. According to some analysts, the proportion of fat experiences an increase, but it is more probable that this constituent is simply rendered more susceptible to the action of solvents by a mechanical alteration of the structure of the berry. Recent determinations of the ash in coffee place its average proportion at 4 per cent.; 3·24 being soluble in water, and 0·74 per cent. insoluble. The soluble extract in roasted coffee usually amounts to about 30 per cent.

An analysis made by Beckurts and Kauder[10] gives the general composition of roasted chicory, dried at 107°, as follows:—

The most common adulterations to which coffee is liable consist in the addition of chicory, caramel, and numerous roasted grains, such as corn, wheat, and rye, as well as such roots and seeds as dandelion, mangold wurzel, turnips, beans, peas, etc. The roasted and ground article is naturally most exposed to falsification, although letters patent have been issued for the fictitious manufacture of a pressed “coffee bean,” containing absolutely no coffee. The addition of chicory is by far the most prevalent adulteration of coffee. Of thirty-four samples examined by Hassall, thirty-one (91 per cent.) contained this root. In regard to the moral aspects of its use, it can safely be asserted that, while the addition of chicory to coffee is largely sanctioned, and indeed demanded by the existing tastes of many coffee-drinkers, its use constitutes a true adulteration, and should be condemned, unless its presence is prominently stated on the label of the package. In chicory the active principles of coffee, which exert valuable physiological effects on the system (viz. caffeine, the essential oil, etc.), are totally absent; moreover, its comparative cheapness is a constant temptation to employ a proportion largely in excess of the amount requisite to produce any alleged improvement in the flavour of the resulting admixture.

The sophistications of coffee may be detected, in a general way, by physical tests, by chemical analysis, and by microscopic examination, in which processes great aid is derived from the characteristic properties exhibited by the pure roasted and ground berry which distinguish it from its more usual adulterants.

(a) Physical Examination.—The following tests, while not always decisive in their results, are often of service.

A small portion of the suspected sample is gently placed upon the surface of a beaker filled with cold water, and allowed to remain at rest for about fifteen minutes. If pure, the sample does not imbibe the water, but floats upon the surface without communicating much colour to it; if chicory or caramel be present, these substances rapidly absorb moisture and sink, producing brownish-red streaks in their descent, which, by diffusion, impart a very decided tint to the entire liquid. A similar coloration is caused by many other roasted roots and berries, but not so quickly or to so great an extent. The test may be somewhat modified by shaking the sample with cold water, and then allowing the vessel to stand aside for a short time. Pure coffee rises to the surface, little or no colour being imparted to the water; chicory, etc., fall to the bottom as a sediment, and give a brownish colour to the liquid.

If a small quantity of the sample is placed upon a clean plate of glass, and moistened with a few drops of water, the pure coffee berries remain hard, and offer resistance when tested with a needle; most grains employed for their adulteration become softened in their texture.

A considerable portion of the mixture is treated with boiling water and allowed to settle. Genuine coffee affords a clear and limpid infusion; many foreign grains yield a thick gummy liquor, resulting from the starchy and saccharine matters contained. An infusion of pure coffee, if treated with solution of cupric acetate and filtered, will show a greenish-yellow colour; if chicory be present, the filtrate will be reddish-brown. As a rule, samples of ground coffee which are much adulterated, pack together when subjected to a moderate pressure.

Owing to the low density of a coffee infusion (due to its almost entire freedom from sugar), as compared with that of the infusions of most roots and grains, it has been suggested by Messrs. Graham, Stenhouse and Campbell, to apply the specific gravity determination of the infusion obtained from the suspected sample as a means for detecting adulteration. The results afforded are fairly approximate. The solution is prepared by boiling one part of the sample with ten parts of water and filtering. The following table gives the densities, at 15°·5, of various infusions made in this manner:—

Assuming the gravity of the pure coffee infusion to be 1·0086, and that of chicory to be 1·0206, the approximate percentage of coffee, C, in a mixture, can be obtained by means of the following equation, in which D represents the density of the infusion:—

C = 1·00(1·020 - D) 12.

This was tested by mixing equal parts of coffee and chicory, and taking the specific gravity of the infusion; it was 1·01408, indicating the presence of 49 per cent. of coffee. Some idea of the amount of foreign admixture (especially chicory) in ground roasted coffee may be formed from the tinctorial power of the sample. It has already been mentioned that coffee imparts much less colour to water than do most roasted grains and roots. The table below shows the weights of various roasted substances which must be dissolved in 2·000 parts of water in order to produce an equal degree of colour:[11]—

The comparative colour test may also be applied as follows:[12]—One gramme each of the sample under examination, and of a sample prepared by mixing equal parts of pure coffee and chicory, are completely exhausted with water, and the infusions made up to 100 c.c. or more; 50 c.c. of the filtered extract from the suspected sample are then placed in a Nessler cylinder, and it is determined by trial how many c.c. of the extract from the standard mixture, together with enough distilled water to make up the 50 c.c., will produce the same colour. In calculating the chicory present, it is assumed that this substance possesses three times the tinctorial power of coffee.

(b) Chemical Examination.—Some of the chemical properties of roasted coffee afford fairly reliable means for the detection of an admixture of chicory. Coffee ash dissolves in water to the extent of about 80 per cent.; of the ash of roasted chicory only about 35 per cent. is soluble. Coffee ash is almost free from silica and sand, which substances form a notable proportion of the constituents of the ash of chicory.

The following (see p. [36]) are the results obtained by the writer from the analysis of the ash of coffee and chicory.

It will be observed from these analyses, that the most distinctive features presented by coffee ash are the absence of soda, and the small amounts of chlorine, ferric oxide and silica present. In these respects, it is very different from the ash of chicory. The proportion of phosphoric acid found in the latter is in excess of that given by some authorities. Several analyses of chicory ash have been made by the author, and, in every instance, the amount of phosphoric acid was over 8 per cent.; in one sample of the ash of commercial chicory it approximated 13 per cent.

Blyth gives the annexed table, showing the characteristic differences between coffee and chicory ash:[13]—

The following formula has been suggested for determining the percentage of pure coffee, in mixtures:—

C = 2 (100S - 174)3

where S represents the percentage of soluble ash.

Another noteworthy difference between roasted coffee and chicory, is the amount of sugar contained. As a rule, in roasted coffee, it ranges from 0·0 to 1·2 per cent.; in roasted chicory, it varies from 12· to 18· per cent. The quantity of sugar in a sample can be determined by Fehling’s method as follows:—

A standard solution of pure cupric sulphate is first prepared by dissolving 34·64 grammes of the crystals (previously ground and dried by pressing between bibulous paper) in about 200 c.c. of distilled water; 173 grammes of pure Rochelle salt are separately dissolved in 480 c.c. of a solution of sodium hydroxide of sp. gr. 1·14. The solutions are then mixed and diluted with distilled water to one litre. Each c.c. of the above solution represents 0·05 gramme of grape sugar. The test is applied by taking 10 c.c. of the copper solution, adding about four times its volume of water, and bringing it to the boiling point. The coffee infusion is then gradually added from a burette, until the copper salt is completely reduced to the red sub-oxide, which point is recognised by the disappearance of its blue colour, and can be more accurately determined by acidulating the filtered fluid with acetic acid and testing it (while still hot) for any remaining trace of copper with potassium ferrocyanide. In preparing the coffee solution for the foregoing test, it is advisable to exhaust a weighed quantity of the sample with hot water. The infusion is treated with basic plumbic acetate so long as a precipitate forms; it is then filtered, the precipitate being well washed, and the lead contained is removed by conducting sulphuretted hydrogen gas through the fluid which is subsequently again filtered and boiled until the dissolved gas is expelled. The sugar determination is now made. Wanklyn employs the following equation to estimate the amount of chicory in an adulterated sample:—

E = (S - 1)100 14,

where E is the percentage of chicory, and S the percentage of sugar.

According to the analysis of König, the proportions of sugar and other constituents in some of the adulterants of coffee, are as follows:—

Estimations of the amount of sugar obtained upon boiling the suspected coffee with water containing a little sulphuric acid (see p. 37), and the proportion of the sample which is soluble in hot water should be made. The presence of chicory is shown by a decided increase in the amount of soluble substances; that of rye, by the notable quantity of sugar produced by the inversion with acid, due to the starch contained in the grain.

In this connection, the following determinations of Krausch are of interest:—

The presence of roasted rye, corn, and other grains in coffee, may be qualitatively recognised by testing the cold infusion of the sample with iodine solution for starch, which is not contained in a ready formed state in coffee. Caffeine is absent in chicory and the other usual adulterants of coffee, and the estimation of this alkaloid is of decided service (see p. [21]). Roasted coffee contains about 1 per cent. of caffeine.

A popular brand of ground coffee received by the author for examination, and labelled “Prepared Java Coffee,” had the following approximate composition:—Coffee, 38; peas, 52; rye, 2; and chicory, 7 per cent.

A sample of “acorn” coffee, analysed by König, gave the following results:—

The non-nitrogenous constituents contained from 20 to 30 per cent. of starch, and from 6 to 8 per cent. of tannic acid.

The composition of the well-known German coffee-substitutes, prepared by Behr Bros., is stated to be as follows:—

“Rye Coffee-substitutes.”

“Malt Coffee-substitute.”

The raw coffee bean is sometimes subjected to a process termed “sweating,” which consists in treating it with moist steam, the object being to artificially reproduce the conditions present in the holds of vessels, by means of which the bean is increased in size, and also somewhat improved in colour and flavour. Another form of manipulation, analogous to the facing of tea, is to moisten the raw bean with water containing a little gum, and agitate it with various pigments, such as indigo, Prussian blue, Persian berries, turmeric, alkanet, Venetian red, soap-stone, chrome-yellow, and iron ochre. Mexican coffees are sometimes made to resemble the more expensive Java in appearance. The chemist of the New York City Board of Health has found in the quantity of such treated coffee commonly taken to make a cup of the beverage 0·0014 gramme of cupric arsenite. Indigo may be detected in the artificially coloured product by treating a considerable portion of the sample with dilute nitric acid, filtering and saturating the filtrate with sulphuretted hydrogen. If indigo be present, it can now be extracted upon agitating the solution with chloroform. Alkanet root and Prussian blue are separated by warming the coffee with solution of potassium carbonate, from which these pigments are precipitated upon addition of hydrochloric acid.

(c) Microscopic Examination.—Great aid to the chemical investigation is afforded by the microscopic examination of ground coffee. It is necessary to first become familiar with the appearance of the genuine article—low magnifying powers being employed—and then make comparative examinations of the adulterant suspected to be present.

The coffee bean mainly consists of irregular cells inclosed in very thick walls which are distinguished by uneven projections. The cells contain globules of oil. Most of the roots added to coffee exhibit a conglomeration of cells (provided with thin walls) and groups of jointed tubes, often quite similar to one another in structure. The microscopic appearance of some of the starch granules, occasionally met with in coffee mixtures, is represented on p. [100].

Of 151 samples of ground coffee recently purchased at random and tested by various American chemists, 69 (45·7 per cent.) were found to be adulterated.

COCOA AND CHOCOLATE.

Cocoa is prepared from the roasted seeds of the tree Theobroma cacao, of the order Byttneriaceæ. It sometimes appears in commerce as “cocoa-nibs” (i. e. partially ground), but it is more frequently sold in the powdered state, either pure or mixed with sugar and starch, and also often deprived of about one-half of its fat. Chocolate usually consists of cocoa-paste and sugar flavoured with vanilla, cinnamon, or cloves, and commonly mixed with flour or starch. According to Wanklyn, the average composition of cocoa is as follows:—

R. Benzeman[14] has furnished the following averages of the results obtained by the analysis of cocoa and chocolate. The air-dried cocoa berries gave—husks, 13·00 per cent.; nibs, 87·00 per cent.:—

Recent analysis of shelled cocoa-beans, made by Boussingault, gave the following results:—

Dr. Weigman[15] obtained the following results from an examination of several varieties of the shelled beans:—

The most important constituents of cocoa are the fat (cocoa-butter), and the alkaloid (theobromine).

Cocoa butter forms a whitish solid of 0·970 specific gravity, fusing at 30°, and soluble in ether and in alcohol.

Theobromine (C7H8N4O2) crystallises in minute rhombic prisms, which are insoluble in benzol, but dissolve readily in boiling water and alcohol. It sublimes at 170°. Theobromine is exceedingly rich in nitrogen, containing over 20 per cent. of the element. In this and many other respects it bears a great resemblance to theine.

The proportion of mineral ash in cocoa varies from 3·06 to 4·5 per cent.

James Bell[16] gives the following composition of the ash of Grenada cocoa nibs:—

The most characteristic features of the ash of genuine cocoa are its great solubility, the small amounts of chlorine, carbonates, and soda, and the constancy of the proportion of phosphoric acid contained. Bell has also analysed several samples of commercial cocoa. The following will serve to illustrate their general composition:—

The comparatively low percentage of ash contained in prepared cocoas and chocolate, is of use in indicating the amount of real cocoa present in such mixtures. A large proportion of the mineral constituents of cocoa are dissolved by directly treating it with cold water. Wanklyn obtained in this way from genuine cocoa-nibs 6·76 per cent. organic matter, and 2·16 per cent. ash, the latter chiefly consisting of phosphates; a commercial cocoa gave, extract, 46·04 per cent.; ash, 1·04 per cent. The most common admixtures of cocoa and chocolate, are sugar and the various starches. The addition of foreign fats, chicory, and iron ochres, is also sometimes practised. Since prepared cocoas are generally understood to contain the first-named diluents, their presence can hardly be considered an adulteration, if the fact is mentioned upon the packages. Many varieties of the cocoas of commerce will be found to be deficient in cocoa-butter, a considerable proportion of which has been removed in the process of manufacture. This practice is also claimed to be justifiable, the object being to produce an article unobjectionable to invalids, which is not always the case with pure cocoa. In the analysis of cocoa the following estimations are usually made:—

Theobromine.—10 grammes of the sample are first repeatedly exhausted with petroleum-naphtha. The insoluble residue is mixed with a small quantity of paste, prepared by triturating calcined magnesia with a little water, and the mixture evaporated to dryness at a gentle heat. The second residue is boiled with alcohol and the alcoholic solution of theobromine filtered and evaporated to dryness in a tared capsule. It is then purified by washing with petroleum-naphtha and weighed. Bell has verified the existence in cocoa of a second alkaloid, distinct from theobromine, which crystallises in silky needles very similar to theine.

Fat.—The proportion of fat is readily determined by evaporating to dryness the petroleum-naphtha used in the preceding estimation. As already stated, it is generally present in a proportion of 50 per cent. in pure cocoa; the amount contained in prepared soluble cocoas being often less than 25 per cent. The English minimum standard is 20 per cent.

Ash.—The ash is determined by the incineration of a weighed portion of the sample in a platinum dish. In prepared cocoas and chocolates, the proportion of ash is considerably lower than in pure cocoa. It is of importance to ascertain the amount of ash soluble in water (the proportion in genuine cocoa is about 50 per cent.), and especially the quantity of phosphoric acid contained. Assuming that prepared cocoa contains 1·5 per cent. of ash, of which 0·6 per cent. consists of phosphoric acid, and allowing that pure cocoa contains 0·9 per cent. of phosphoric acid, Blyth adopts the following formula for calculating the proportion of cocoa present in the article:—

·6 × 100 ·9 = 66·66 per cent.

Starch.—A convenient method for estimating the starch is to first remove the fatty matter of the cocoa by exhaustion with petroleum-naphtha, and then boil the residue with alcohol. The remaining insoluble matter is dried, and afterwards boiled until the starch becomes soluble. It is next again boiled for several hours with a little dilute sulphuric acid, after which the solution is purified by addition of basic plumbic acetate. The liquid is then treated with sulphuretted hydrogen, in order to remove the lead, and the sugar contained in the filtered solution is determined by means of Fehling’s solution, and calculated to terms of starch. The proportion of starch normally present in cocoa is to be deducted from the results thus afforded. The variety of starch contained in cocoa differs in its microscopic appearance from the starches most frequently added.

Sugar.—The sugar may be determined by evaporating the alcoholic solution obtained in the preceding process, and then subjecting the residue to the same method of procedure.

The proportion of woody fibre in cocoa can be approximately estimated by the method of Henneberg and Stohman,[17] which consists in extracting the fat with benzole, boiling the remaining substances for half an hour, first with 1·25 per cent. sulphuric acid, then with 1·25 per cent. solution of potassium hydroxide. The residue is washed with alcohol and with ether, and its weight determined. Unwashed cocoa-berries, when treated in this manner, gave from 2 to 3 per cent. of cellulose, while cocoa husks furnished from 10 to 16 per cent. The presence of chicory in soluble cocoa and chocolate is easily recognised by the dark colour of the extract obtained, upon digesting the suspected sample with cold water; ochres and other colouring matters are detected by the reddish colour of the ash as well as by its abnormal composition. The addition of foreign fats to chocolates is stated to be occasionally resorted to.

The melting point of pure cocoa-butter varies from 30° to 33°. The identification of foreign fats can sometimes be accomplished by means of their higher melting point, and by an examination of the separated fat, according to Koettstorfer’s method (see p. [71]). The table following gives the melting points of various fats, and the number of milligrammes of K(OH) required for the saponification of one gramme of the same.

Other tests have also been suggested for the detection of foreign fats in cocoa-butter:—

(a) Treat the fat with two parts of cold ether; pure cocoa-butter dissolves, forming a clear solution, whereas in presence of tallow or wax a cloudy mixture is obtained.

(b) Dissolve 10 grammes of the suspected fat in benzole, and expose the solution to a temperature of 0°. By this treatment a separation of pure cocoa-butter in minute grains is produced. The liquid is now heated to 14°·4, when the cocoa-fat will re-dissolve to a transparent solution, while the presence of tallow will be recognised by the turbid appearance of the liquid.

MILK.

Owing to the very important sanitary relations of milk as a model food, the subject of its sophistication has during the past ten years received particular notice at the hands of the food-chemist. The investigations of our public sanitary authorities have shown that milk adulteration is exceedingly common. It is stated upon good authority that until quite recently (1883) the 120 millions of quarts of milk annually brought into New York city were intentionally diluted with 40 millions of quarts of water, the resulting product rivalling in richness the famous compound once lauded by the philanthropic Squeers.

The results of the examination of milk instituted by the New York State Board of Health are given below, in which, however, the specimens of skimmed milk are not included:—

From October 1883 to March 1884, of 241 samples of milk examined by the Public Analyst of Eastern Massachusetts, 21·37 per cent. were watered; of 1190 samples tested during the year 1884, 790 were watered.[18] Over 73 per cent. of the milk supplied to the city of Buffalo in 1885 was found to be adulterated. A very marked improvement in the quality of the milk received in New York city has taken place since the appointment of a State Dairy Commissioner (1884). Under the direction of this official the metropolitan milk supply has been subjected to a most rigid inspection, and with very satisfactory results. During the years 1884 and 1885 nearly 45,000 samples of milk were examined.

A very common sophistication practised upon milk consists in the partial or complete removal of its cream. This process of skimming is conducted at establishments called “creameries,” of which sixty-three were formerly known to send their impoverished product to New York city. The State Dairy Commissioner has likewise accomplished much towards stopping this form of adulteration.

Milk is the secretion of the mammary glands of female mammalia. It is an opaque liquid, possessing a white, bluish-white, or yellowish-white colour, little or no odour, and a somewhat sweetish taste. At times it exhibits an amphigenic reaction, i. e. it turns red litmus blue and blue litmus red. From the examination of nearly one thousand cows in the States of New York, New Jersey, and Connecticut, the minimum specific gravity of milk was found to be 1·0290, the maximum being 1·0394. The opacity of milk is only apparent, and is due to the presence of fatty globules held in suspension; these under the microscope are seen to be surrounded by a transparent liquid. Upon allowing milk to remain at rest for some time it experiences two changes. At first, a yellowish-white stratum of cream rises to the surface, the lower portion becoming bluish-white in colour and increasing in density. If this latter is freed from the cream and again set aside, it undergoes a further separation into a solid body (curd), and a liquid (whey). This coagulation of the curd (caseine) is immediately produced by the addition of rennet, and of many acids and metallic salts.

The essential ingredients of milk are water, fat, caseine, sugar (lactose), and inorganic salts. The following table, collated by Mr. Edward W. Martin,[19] exhibits the results obtained by numerous authorities from the analysis of pure cow’s milk:—

Mr. Martin obtained the following results from the examination of cream separated by centrifugal force, and of skimmed milk:—

The proportion of mineral constituents in milk usually ranges between 0·7 and 0·8 per cent. The average composition of milk ash is as follows:[20]—

The tabulation below gives the composition of human milk and the milk of various animals:—

Several varieties of preserved and condensed milk have, for a number of years, been placed upon the market. The composition of the best-known brands of these preparations is as follows:—

Preserved Milk.

Condensed Milk.

Analysis.

The principal adulterations of milk (watering and skimming), are detected by taking its specific gravity, and making quantitative determinations of the total milk solids, the fat, and the milk solids not fat. Of these criteria, the last-mentioned is the most constant and reliable.

Physical Examination.

a. Specific Gravity.—The instrument employed by the New York health inspectors for testing milk is a variety of the hydrometer, termed the lactometer, and its use, which is based upon the fact that under ordinary conditions watered milk possesses a decreased density, is certainly of great value as a preliminary test. The Board of Health lactometer indicates specific gravities between 1·000 (the density of water) and 1·0348. On its scale 100° represents the specific gravity of 1·029 (taken as the minimum density of genuine milk), and 0 represents the density of water; the graduations are extended to 120°, equivalent to a specific gravity of 1·0348. In taking an observation with the lactometer, the standard temperature of 15° should be obtained, and the colour and consistency of the milk noted. If these latter properties indicate a dilution of the sample, and the instrument sinks below the 100° mark, it is safe to assume that the milk has been watered. The scale is so constructed that the extent of the dilution is directly shown by the reading, e. g. if the lactometer sinks to 70° the sample contains 70 per cent. of pure milk and 30 per cent. of water. As the standard of specific gravity (1·029) selected for the 100° mark of the lactometer is the minimum density of unwatered milk, it is evident that the readings of the instrument will almost invariably indicate an addition of water less than has actually taken place. It would therefore appear that, under normal circumstances, the standard adopted by the New York Board of Health errs on the side of too much leniency toward the milk dealer. Cream being lighter than water, a sample of skimmed milk will possess a greater specific gravity than the pure article, and it is possible to add from 10 to 20 per cent. of water to it and still have the resulting admixture stand at 100° when tested by the lactometer. Vehement attempts have been made in court and elsewhere to impeach the accuracy of the indications afforded by the lactometer. These have been mainly founded upon the fact that a sample of milk unusually rich in cream will have a lower density than a poorer grade, so that it is quite possible that milk of very superior quality may show a gravity identical with that of a watered specimen. Great stress has been laid upon this by the opponents of the measures to control milk adulteration adopted by the public sanitary authorities. They have contended that a chemical analysis should be made. Recourse to this method would, however, involve a greater amount of time than it is usually practicable to devote to the examination of the numerous samples daily inspected; moreover, the process is resorted to whenever the indications of the lactometer leave the inspector in doubt. With the exercise of ordinary intelligence this contingency seldom arises, as the proportion of cream required to reduce the specific gravity to that of a watered sample would be more than sufficient to obviate any danger of mistaking the cause of the decreased density. In this connection it should be stated, that the average lactometric standing of about 20,000 samples of milk, examined by the New York State Dairy Commissioner in the year 1884, was 110°, equivalent to a specific gravity of 1·0319.

The following table shows the value of lactometer degrees in specific gravity:—

Value of Lactometer Degrees in Specific Gravity.

Chemical Examination.

b. Water, Total Solids, and Ash.—Five grammes of the fresh milk are weighed in a tared platinum dish, having a flat bottom, which is placed on a water-bath, where it is allowed to remain for about three hours. It is then transferred to a water-oven, and the dish is subsequently weighed, from time to time, until the weight becomes constant. The loss in weight is the water present; the difference between the weight of the platinum capsule and its weight with the remaining contents gives the amount of total solids, which, in milk of good quality, should not be under 12 per cent. The inorganic salts (ash) can now be determined by carefully incinerating the residual contents of the capsule. Too high a temperature is to be avoided in this process, in order to prevent the fusion of the ash, which should, however, be ignited until it shows a greyish-white colour. The amount of ash in genuine milk ranges from 0·70 to 0·80 per cent. The addition of water naturally decreases this proportion as well as that of the total milk-solids.

c. Fat, Milk Solids not Fat, Caseine, and Milk Sugar.—An approximate estimation of the fat in milk was formerly made by the use of the creamometer. This instrument consists simply of a long glass tube, provided at its upper end with a scale. The milk under examination is introduced into the tube and allowed to remain at rest for about 24 hours, or until the stratum of cream has completely collected upon its surface; the quantity is then read off by means of the attached scale. The results afforded by the creamometer are, however, far from reliable. Cream is really milk rich in fat, caseine, etc., and the quantitative relation it bears to the true amount of fat present is not always a direct one. A recent form of lactoscope, devised by Feser, is less objectionable, and is in very general use for the rapid estimation of fat in milk. It consists essentially of a glass cylinder, provided with two scales, one being graduated into c.c., the other, into percentages of fat. In the lower end of the instrument is a contraction, in which is placed a cylindrical piece of white glass, graduated with well-defined black lines. In using the lactoscope, 4 c.c. of the milk are introduced into the instrument by means of a pipette, and water is gradually added, with shaking, until the black marks on the small white cylinder become just visible. Upon now referring to the c.c. scale, the quantity of water used to effect the necessary dilution is ascertained, and the corresponding percentage of fat in the sample is indicated by the percentage scale.[22]

In the gravimetric determination of the fat (butter), 10 grammes of the milk are put into a tared platinum dish, containing a weighed amount of dry sand. The milk is evaporated as previously directed, the mixture being constantly stirred with a small platinum spatula. The residue is repeatedly treated with warm ether or petroleum naphtha of 70° B., and the solutions poured upon a small filter. The several filtrates are collected in a tared beaker, and cautiously evaporated, until constant weight is obtained. This will give the amount of fat. The undissolved residue remaining in the platinum capsule, or the difference between the quantity of fat and that of the total milk-solids, affords the proportion of milk solids not fat contained, which, in unadulterated milk, should amount to 9 per cent. It has been determined by experiment, that every percentage of milk-solids not fat, increases the specific gravity of milk 0·00375, whereas each percentage of fat decreases the gravity 0·0010, and the proportion of solids not fat can be calculated from the data afforded by the lactometer and Feser’s lactoscope by means of the formula:—

(S - A) 0·00375 ,

where S is the specific gravity of the milk, as shown by the lactometer, and A is the remainder obtained upon multiplying the percentage of fat indicated by the lactoscope by 0·001 and subtracting the residue from 1·0000.

The residue remaining after the extraction of the fat is treated with warm water containing a few drops of acetic acid, or with dilute (80 per cent.) alcohol, in order to remove the sugar. The residue is dried until it ceases to decrease in weight, and is then weighed. The difference between the original weight of the sand and the weight of the sand and residue combined represents approximately the amount of caseine (albuminoids) present. As this contains a certain proportion of ash it is to be subsequently ignited, and the ash obtained deducted from the first weight. The alcoholic sugar solution is evaporated to dryness and weighed. The residue is then incinerated and the weight of ash is subtracted. The difference is the amount of milk sugar contained. The sugar may likewise be determined by means of Fehling’s solution (see pp. 37, 111). About 50 c.c. of the milk is warmed with a small quantity of acetic acid to precipitate the caseine, which is removed by filtration, and the filtrate diluted to 500 c.c.; the test is then applied. 10 c.c. of the copper solution represents 0·067 gramme of milk sugar.

The sugar in milk can also be estimated by the polariscope (see under Sugar, p. [112]). In case the Ventzke-Scheibler instrument is used, 65·36 grammes of the sample are weighed out and introduced into a 100 cc. flask; about 5 cc. of plumbic basic acetate solution is added, and the liquid is well shaken, and then allowed to stand at rest for a few minutes. It is next filtered, its volume made up to the 100 cc. mark, and the 20 cm. tube filled and the reading made; this divided by 2 gives the percentage of sugar in the milk.

Mr. A. Adams[23] has recently proposed a method of milk analysis which consists in first placing 5 cc. of the sample in a tared beaker, and then introducing a weighed paper coil made of blotting paper from which all fatty matter has previously been removed by washing with ether. As soon as the milk is completely absorbed, the paper coil is removed and dried at 100°. The increase of weight gives the amount of total solids. The fat is next extracted by petroleum naphtha or ether, and its weight determined. The proportion of solids not fat is ascertained by again drying and weighing the exhausted coil.

The standards adopted by the English Society of Public Analysts for pure milk, are:—

In the State of New York, the legal standards for milk are that it shall not contain more than 88 per cent. of water, nor less than 12 per cent. of milk solids, and 3 per cent. of fat.

In Massachusetts the law fixing a chemical standard of purity for milk reads: “In all cases of prosecution, if the milk shall be shown upon analysis to contain more than 87 per cent. of water, or to contain less than 13 per cent. of milk solids, it shall be deemed, for the purpose of this Act, to be adulterated.”

The Board of Health of New Jersey fixes the minimum amount of total solids at 12 per cent. and the maximum amount of water at 88 per cent. In Paris, the minimum limits for condemnation are the following:—

Fat, 2·70; milk-sugar, 4·50; caseine, albumen, and ash, 4·30; total solids, 11·50.

The following proportion can be employed in the calculation of the amount of pure milk (x) contained in a suspected sample:—

From the total solids:—

12·5: total solids found = 100 : x.

From the solids not fat:—

9·30: solids not fat = 100 : x.