Lime.—Into a glass of the water put 2 drops oxalic acid, and blow upon it; if it gets milky, lime is present.
Acid.—Take a piece of litmus paper. If it turns red, there must be acid. If it precipitates on adding lime water, it is carbonic acid. If a blue sugar-paper is turned red, it is a mineral acid, and there would be reason to suspect poisonous metallic salts.
Foods.—Foods are adulterated in three principal ways, viz.:—(1) By replacing a superior article or ingredient by an inferior or cheaper substitute, (2) by adding foreign matters capable of giving an appearance of superiority, (3) by adding water to increase the weight, this being often accompanied by incorporating foreign materials which absorb much water though perhaps otherwise harmless.
Bread.—Pure flour (wheaten) may be replaced by various meals of inferior nutritive value and lower price; if done on a scale to repay the baker, their presence can be at once detected under the microscope. This kind of adulteration is nearly always accompanied by the use of alum, which improves the appearance of bread made from inferior flour, and enables it to hold much more water. The presence of alum can be ascertained easily and rapidly by the logwood test: soak some crumbs of bread for 6 or 7 minutes in an alcoholic solution of logwood containing an excess of carbonate of ammonia, and squeeze it—a more or less deep blue colour is produced. Alum is often used too to hide the employment of damaged flour, containing perhaps only 7 per cent. of gluten instead of 12. The presence of mineral adulterants, which seldom occurs, is proved by burning a sample of the bread and weighing the ash, which should not exceed 7 parts in 1000. Bread is sometimes made of the flour from wheat which has “sprouted” or germinated, and is then inferior. This can only be ascertained by examining the flour: if it has a musty odour and flavour and an acid reaction, the flour has probably been damp for some time; if there is no mustiness but only an acid reaction, sprouted wheat has been employed. The acid reaction is best discovered by stirring some of the flour in water, filtering, and testing with a solution of corallin rendered red with a trace of alkali; if the flour is acid it turns yellow.
Butter.—Cheap butters largely consist of admixtures with other animal fats, especially that known as “butterine” or “bosch.” Analysis of suspected butter could hardly be undertaken by the housewife, but the presence of butterine is probable if the butter breaks in a crumbly manner and loses its colour on being kept melted for a short time at the temperature of boiling water (212° F.).
Milk.—Adulteration chiefly consists in adding water to skim milk and in mixing skim milk with that sold as new. Analysis is possible only to the skilled chemist, but a rough test may be made. The lactoscope devised by Dr. Bond, of Gloucester, is based on the principle of that of Prof. Feser, of Munich, in which the opacity of fresh milk is taken as proportionate to the amount of butter fat. It is useful as providing a ready means of determining with approximate accuracy the richness of milk, and is therefore a rough but sufficient test where adulteration is suspected. As supplied by the Sanitary and Œconomic Association of Gloucester, it consists of a little glass dish with some black horizontal lines on the base, a small measure, and a sort of pipette. The measure is filled with water and emptied into the dish; the pipette is filled with the milk to be tested, which is then dropped into the water, the drops being counted. The mixture of water and milk is stirred, and when the horizontal lines can no longer be seen, say, from a height of 2 ft., the number of drops of milk used are compared with a table supplied, and the approximate amount of butter-fat is read off. This instrument must not be confounded with the various lactometers, which aim at estimating the quality of a milk by its density (specific gravity)—an utterly erroneous proceeding, seeing that a poor milk will often show a higher density than a rich one.
For new milk a capital test is to pour a small quantity into an ordinary glass test-tube graduated from 0 at the top to 100 at the bottom; on allowing the sample to stand, cream will form, and its proportion can be read off at a glance, always allowing 20 hours’ rest. Good new milk should show an average of 11½ per cent. of cream, and will sometimes reach 80 per cent. The quality of skim milk is less easy to estimate by ready means. It should average not less than 1 part of fat in 1000.
As a precaution against possible infection by diseased milk, it is advisable to let all milk be boiled before use, as the boiling temperature is fatal to the disease germs. Such milk, however, is not so digestible or palatable to many people.
Tea.—The present low prices of tea do not afford much scope for profitable adulteration in this country. The chief falsifications to be on the look out for are the artificial colouring of green teas, which, naturally, are hardly distinguishable from black; and the substitution of re-rolled exhausted leaves for genuine fresh leaves. There is also in cheap teas often a considerable proportion of mineral matter, i.e. added dirt. This last can be readily detected by chewing a small quantity of the leaf, when dirt will be felt in the mouth. The presence of exhausted leaves will be manifested by the increased weight of solid matters left on boiling a sample repeatedly and drying the residue. With genuine teas, the average weight of leaves (dried) remaining after exhaustion is 65 per cent.; therefore 1 oz. of tea thoroughly boiled should not give more than ⅔ oz. of exhausted leaves weighed after drying. If the figure is higher, the addition of exhausted leaves to the original tea may be suspected.
Coffee.—Coffee-berries can scarcely be adulterated without easy detection, therefore the best safeguard is to buy the berries and grind them at home. Ground coffee is nearly always adulterated with chicory: in fact a certain proportion is allowed by law, and the chicory is itself often largely mixed with various rubbish which by roasting gives a brown colour to water. The simplest plan for detecting the sophistication of ground coffee is to sprinkle some in a glass of cold water: pure coffee will not colour the water for some time, while chicory and its substitutes will do so immediately.