about 0.52 mm. [00021 inch], and are often seen to have a somewhat obscure starred hilum. They strike a pronounced blue colour with iodine.

The husk contains from without inwards the following structures:

(1.) A superficial layer of large, very characteristic tubular fibres, containing granular matter and little corpuscles.

(2.) A single layer of elongated cells, with their greatest diameter transversely to the axis.

(3.) Large angular cells in several layers; those in the centre mucilaginous, constituting the greatest bulk of the envelope.

(4.) A very delicate membrane, formed of small cells, enclosing fatty matters. This membrane adheres to the almond, and portions of it may always be seen in the chocolates of commerce.

Another hyaline and fibrous structure connected with the last, and full of crystals, is usually described, as well as isolated, dark, elongated bodies. The whole structure, therefore, is complex in a high degree, but familiarity with the appearance presented by the different portions of the seeds is readily obtained.

§ 220. The commercial varieties of cocoa are very numerous :Cocoa nibs are simply the bruised, roasted seeds deprived of their coverings; and flake cocoa is composed of the nibs ground in a particular form of mill. The soluble cocoas are-ground cocoa, diluted with sugar and starches-e.g.,

Epps's cocoa, according to an analysis advanced as evidence in the case of Gibson v. Leafer, is composed of cocoa 40 per cent., sugar 44 per cent., and starch 16 per cent.

Granulated cocoa is mostly a mixture of nibs, arrow-root, and sugar; Homœopathic cocoa, a preparation of the same kind without the sugar; Maravilla cocoa contains sugar and much sago flour; and cocoa essence, cocoatine, &c., consist of pure cocoa deprived of 60 to 70 per cent. of its fat.

The above are examples only. The analyst is liable to meet any day with some new patent cocoa, for the consumption of this food is greatly on the increase.

§ 221. Chocolate.—In the manufacture of chocolate the cocoanibs are ground in a mill, the rollers of which are usually heated by steam, so as to soften the cocoa-butter; and in this way a paste is formed which is mixed with refined sugar, and very often other substances, and pressed into moulds. Some of the receipts for chocolate are as follows :—

* That the consumption of cocoa is increasing is evidenced by the quantity imported-in round numbers, 10,000,000 lbs. in 1876, against 9,000,000 lbs. in 1875.

(1.) French Chocolate.—2 beans of Vanilla rubbed into a powder with sugar, and 1 lb. of best sugar to every 3 lbs. of cocoa nibs. (2.) Spanish Chocolate.-(a.) Curaçoa cocoa 11, sugar 3, Vanilla cinnamon, cloves 12 (b.) Caraccas cocoa 10, sweet almonds 1, sugar 3, Vanilla 4.

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Vanilla Chocolate.-A chocolate paste highly flavoured with Vanilla, and generally with other spices as well. (a.) Caraccas cocoa 7, Mexican Vanilla, cinnamon, and sufficient cloves to flavour. (b.) Best chocolate paste 21, Vanilla 4, cinnamon, cloves and musk in small quantities.

The chocolates of English commerce yield but little cocoabutter, since they are mostly prepared from the cake left after expression of the oil.

§ 222. The average chemical composition of cocoa, according to some English analyses, is as follows:

The peculiar constituents of cocoa are then two-viz., cocoabutter and theobromin.

Cocoa-butter, Oleum theobroma, specific gravity, 0.96 to 0.98;* melting point, 29° to 30°; solidifying point, 24°, is a yellowish-white, concrete oil about the consistency of tallow, with a chocolate colour and an agreeable taste. At common temperatures it is brittle, the fracture is smooth and equal, and examined by a lens it is somewhat crystalline. It is fully soluble at ordinary temperatures in two parts of ether, in half a part of benzole, as well as in 100 parts of cold and 20 parts of hot absolute alcohol; its solution is entirely neutral to test paper. If adulterated with tallow, wax, paraffin, or stearin, the specific gravity will be altered, and it will not dissolve to a clear solution in the quantity of ether named above. Pure cocoa butter does not become rancid, however long it is kept; but the admixture of most

*Its specific gravity was formerly given as from 89 to 91; but Fläckiger, as well as Hirsch, has shown that this is too low.

foreign fats impairs this property. Cocoa-butter is usually said to consist of cocoa stearin, which separates in warty masses on evaporating an ethereal solution, and has a melting point of 65° with a little olein. Kingzett has, however, recently described two new fatty acids obtained from cocoa fat, one of which has the empiric formula CH12O2, and the subject appears to require further research. The best method of extracting the fat is to exhaust the nibs with ether in the apparatus figured at page 67.

Cocoa should contain at least 20 per cent. of cocoa fat; if less than that is found, it should be returned as adulterated.*

$223. Theobromin, CH,NO-This alkaloid was discovered in 1841 by Woskresensky, in the seeds of the Theobroma cacao; it principally resides in the cotyledons, and in smaller quantities in the seed-coverings. The average yield of theobromin appears to be 1 per cent.

The original method of separation pursued by Woskresensky was-extraction on the water-bath with distilled water, filtering through linen, precipitating with sugar of lead, refiltering, freeing the filtrate from excess of lead by SH2, evaporating to dryness, and subsequent purifying of the residue by solution in spirit, and treatment with animal charcoal. Mitscherlich, again, boils the cocoa with a weak solution of sulphuric acid in order to change the starch into sugar, saturates the fluid with carbonate of lead, and ferments it with yeast to destroy the sugar. On the conclusion of the fermentation, the fluid is boiled, neutralised with soda, filtered, concentrated by evaporation, and the impure brown theobromin which separates boiled in hot nitric acid. This nitric acid solution is precipitated by ammonia, again dissolved in nitric acid, and the nitrate obtained by evaporation. According to Mitscherlich, the quantity obtained in this way is much greater than by other processes.

A speedy method of determining, with very fair exactitude, the percentage of theobromin in cocoa, is to exhaust a weighed quantity with petroleum ether, mix the residue with a little burnt magnesia and water, evaporate to dryness at 60° to 70°, and then exhaust the residue with boiling alcohol of 80 per cent., which dissolves out the theobromin. On driving off the alcohol by evaporation, the substance may be purified sufficiently for weighing purposes by washing with petroleum ether.

G. Wolfram has recommended the following process for the extraction of theobromin :-10 grms. of the substance are

120 per cent. is the standard of the Society of Analysts; but in the writer's opinion this is much too low, according to published analyses.

powdered and exhausted with hot water, filtered, and the filtrate precipitated by ammoniacal acetate of lead, and the precipitate washed with boiling water, until the filtrate, acidified by sulphuric acid, no longer gives a precipitate with phosphotungstic acid. The filtrate is made alkaline by soda, evaporated to 50 cc., strongly acidified by sulphuric acid, and the lead sulphate filtered off. The filtrate is now precipitated by a large excess of sodium phospho-tungstate, and the precipitate decomposed by hot baryta water; the barium phospho-tungstate is filtered off, and the filtrate freed from baryta by adding sulphuric acid in very slight excess, the excess being got rid off by adding a little barium carbonate. The alkaloid is obtained by filtration, and evaporating the first filtrate to dryness, weighing, and then igniting, and again weighing the difference equals the alkaloid. The ignition is necessary, for there is always a little baryta which has not been got rid of by the previous operations. In six analyses of various cocoas, Wolfram obtained as a maximum, 1.66 per cent.; as a minimum, 1.34 per cent.; and as a mean, 1.56 per cent. of theobromin, in the dried cocoabeans divested of their coverings; while the dried husk of the six cocoas contained maximum 1·11, minimum 42, mean ⚫76 per cent. theobromin.

Theobromin forms microscopic rhombic needles. It is generally thought to sublime between 296° and 295° without decomposition, but this temperature is many degrees too high. The writer finds that a minute fragment, placed in the subliming cell elsewhere described, begins to give fine nebulæ at 134°, and on examining the mists by a high power, they are resolved into extremely minute dots; distinct crystals are obtained at temperatures of 170° and above. Theobromin is insoluble in petroleum ether, and not very soluble in ether, 1 part requiring 600 parts of boiling and 1,700 parts of cold ether. It is soluble in alcohol, I part requiring 47 parts of boiling and 1,460 of cold alcohol. Its solubility in water is stated to be 1 in 55 parts at 100°, 1 in 600 parts at 20°, and 1 in 1,600 at 0°. It is somewhat soluble in chloroform and warm amyl-alcohol, but with difficulty soluble in benzole.

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The simple

Theobromin forms easily crystallisable salts. neutral salts are decomposed by water, with the formation of basic salts, and lose their acid, if it is volatile, at 100°. A hydrochloride of theobromin, C,H,N,O,,HC; a nitrate, CH ̧N402,NHO; a platinum salt, C,H.NO,,HClPtCl2+ 2H2O; are all very definite crystalline compounds. A noteworthy salt is the nitrate of silver, which is formed by adding a solution of argentic nitrate to a solution of nitrate of theobromin; in a short

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time there separate silver-white needles, very insoluble in water, of the composition C,H,NO,NHO, + AgNO3.

The other precipitants of theobromin are-phospho-molybdic acid (yellow) and chloride of gold (long needles). Tannic and picric acids only produce turbidity, while potass. mercuric iodide and potass. cadmium iodide do not precipitate. A characteristic reaction of theobromin is that produced by peroxide of lead and sulphuric acid. If peroxide of lead and diluted sulphuric acid are heated with theobromin, avoiding an excess of the oxidising agent, CO2 is developed, and the colourless filtrate of sulphate of lead gives off ammonia with potash, separates sulphur on treatment with SH, stains the skin purple-red, and colours magnesia indigo-blue.

The

Theobromin is poisonous to kittens (and other animals of similar size) in such large doses as a gramme. It appears to be separated by the kidneys, and could probably be discovered in the urine of any person taking large quantities of cocoa. method of research successfully used by Mitscherlich is as follows:-The urine is acidified with HCl, filtered, and to the filtrate, acidified with nitric acid, a solution of phospho-molybdate of soda is added. The precipitate is collected, and treated with baryta water until it is strongly alkaline, warmed, filtered, and the filtrate evaporated; the residue extracted with alcohol, refiltered, and the filtrate again evaporated. This last residue is dissolved in a drop of hydrochloric acid, and precipitated by ammonia. The alkaloid may now be collected and, if necessary, purified.

§ 224. The Ash.-The composition of the ash of cocoa seeds is stated by Mr. Wanklyn to be as follows:

The percentages of ash found in cocoa are given as follows: