605. Pectic Acid.—Under this term are included not only the pectic acid but all the other bodies of a pectose nature contained in tobacco. These bodies are of considerable interest, although they do not belong to the most important constituents. In fresh tobacco leaves are found three pectin bodies. One pectin is soluble in water, another is an insoluble pectose and the third is the pectose body forming salts with the alkalies, i. e., true pectic acid. In fermented tobacco pectic acid is found chiefly in combination with lime in the ribs of the leaves, serving to give them the necessary stiffness. For the estimation of the pectin bodies (mucilage) the powdered tobacco is thoroughly extracted with cold water. An aliquot part of the aqueous extract is mixed with two volumes of strong alcohol and allowed to stand in a well closed vessel in a cool place for twenty-four hours. The precipitate is collected on a filter, washed with sixty-six per cent alcohol, dried and weighed. The dried residue is incinerated and the amount of ash determined. In general, vegetable mucilages contain about five per cent of ash. If more than this be found, it is due to the solution of the salts of the organic acids contained in the sample. A dried vegetable mucilage, obtained as above, dissolves in water to a mucilaginous liquid which does not reduce alkaline copper solution until it has been hydrolyzed by boiling with a dilute mineral acid.[623]
606. Tannic Acid.—This acid is separated and estimated by the processes given in paragraphs [589-595].
607. Starch and Sugar.—The unfermented leaves of tobacco contain considerable quantities of carbohydrates in addition to woody fiber, pentosans, galactan and cellulose. Among these, starch is the most important. Sugar exists in small quantities in the fresh leaf, usually not over one per cent. During fermentation, according to some authorities, the starch is partially converted into sugar and the latter substance disappears under the action of the alcoholic ferments. It has been found at the Connecticut Station, however, that the starch content of the leaf does not decrease during fermentation. The starch and sugar may be determined in the fresh leaves by the methods already given.
In the manufacture of certain grades of tobacco it is customary to add a quantity of sugar. The analyst may thus be called upon to determine in some cases whether the sugar found in a sample is natural or added. The occurrence of natural sugars in tobacco has been investigated at the instance of the British Treasury.[624]
The natural sugars which may be found in sun dried tobaccos usually disappear entirely during the process of fermentation. It was found by the Somerset House chemists that the content of sugar in commercial tobaccos varies from none at all to over fifteen per cent. A remarkable example of this variation is reported in two samples from this country, one of which, grown in Kentucky, contained no sugar, and the other grown in Virginia, 15.2 per cent.
It was noticed that the saccharin matters in the tobaccos examined were neutral to polarized light. They are determined by their copper reducing power. The tobacco sugars are therefore to be classed with the reducing bodies, not optically active, found in the juices of sorghum and sugar canes.
608. Ammonia.—As has already been intimated, ammonia exists only in minute quantities in fresh tobacco leaves, but in considerable quantities after fermentation. In the estimation of ammonia, twenty grams of the tobacco powder are digested with 250 cubic centimeters of water, acidulated with sulfuric and after an hour enough water added to make the total quantity 400 cubic centimeters. After filtration, an aliquot part of the filtrate, about 200 cubic centimeters, is treated with magnesium oxid in excess and the ammonia and nicotin removed by distillation in a current of steam. The distillate is collected in dilute sulfuric acid of known strength. The total amount of the two bases is determined by titration and the quantity of base representing the nicotin, which has been determined in a separate sample, subtracted in order to obtain the weight of the ammonia.[625]
The ammonia in tobacco is determined by Nessler in the following manner:[626]
The powdered tobacco is mixed with water and magnesium oxid and after standing for several hours it is distilled in a current of steam, the distillate received in dilute sulfuric acid and the process continued until a drop of the distillate gives no reaction for ammonia with the nessler reagent. The excess of sulfuric acid in the distillate is neutralized with pure sodium carbonate and the nicotin precipitated by a neutral solution of mercuric iodid and potassium iodid. The precipitate is separated by filtration, the filtrate treated with sodium sulfid, and the ammonia again obtained by distillation with an alkali, collected in dilute solution of set sulfuric acid and determined by titration. The difference of the two determinations represents the ammonia.
609. Nicotin.—In this laboratory McElroy has made a study of some of the best approved methods for determining nicotin, and finds the most simple and reliable to be that proposed by Kissling.[627] The finely powdered tobacco should be dried at a temperature not exceeding 60°, or it may be partially dried at that temperature before grinding and the final drying completed afterwards. Twenty grams of the powdered sample are intimately mixed by means of a pestle with ten cubic centimeters of dilute alcoholic solution of soda lye, made by dissolving six grams of sodium hydroxid in forty cubic centimeters of water and completing the volume to 100 cubic centimeters with ninety-five per cent alcohol. The mass is transferred to an extraction paper cylinder, placed in an extraction apparatus and extracted for three hours with ether. The ether is nearly all removed by careful distillation, the residue mixed with fifty cubic centimeters of a very dilute soda lye solution (4 to 100) and subjected to distillation in a current of steam. The flask containing the nicotin extract should be connected with the condensing apparatus by a safety bulb as is usual in the distillation of substances containing fixed alkali. The distillation should be conducted rapidly and in such a manner that when 200 cubic centimeters of the distillate have been collected, not more than fifteen cubic centimeters of the liquid remain in the distillation flask. In the distillate, the nicotin is determined by titration with a set solution of dilute sulfuric acid, using rosolic acid or phenacetolin as indicator. It is advisable to titrate each fifty cubic centimeters of the distillate as it is received and the distillation is continued until the last fifty cubic centimeters give no appreciable quantity of the alkaloid. In the calculations one molecule of sulfuric acid is equivalent to two molecules of nicotin according to the equation