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.