[31] The percentage of foreign fat (F) in a sample can be calculated by the formula F = (I - 88) × 13·3, in which I = the insoluble fatty acids. [32] Fresenius’ Zeitschrift, 1879, p. 68. [33] Journ. Amer. Chem. Soc., viii. p. 6. [34] Dingl. Polyt. Journ., ccliii., p. 281. [35] R. W. Moore notes that a certain mixture of lard and cocoa-nut oil would give an iodine number identical with that of butter fat.--(‘Analyst,’ x. p. 224.) [36] Journ. Amer. Chem. Soc., vii. p. 134. [37] Samples invoiced as “butter flavouring,” and consisting of butyric acid, have also been imported. [38] ‘Analyst,’ x. p. 163. [39] Ibid., xi. p. 163. [40] The author is indebted to Mr. Edward W. Martin for the negatives used in the preparation of these and other photomicrographs of fats. [41] _Vide_ ‘Proceedings of the American Microscopical Society,’ May 1885. [42] ‘Bulletin of the Ohio Agricultural Experiment Station,’ March 1st, 1886. [43] Bradstreet’s, June 19, 1886. [44] Fourth Annual Report (1883) Mass. State Board of Health, p. 30. [45] Second Annual Report of the New York State Dairy Commissioner, pp. 291-392. [46] ‘Landwirthschaftliche Versuchsstation,’ ii. p. 215. CHEESE. Cheese consists essentially of the caseine and albumen of milk, together with water, fat, lactic acid, and mineral salts. It is prepared by the coagulation of milk by means of rennet, and is usually obtained from cow’s milk (either fresh, skimmed, or sour), although the milk of the goat, ewe, and other animals is occasionally used. Its colour is very often due to the addition of annato. The following table exhibits the composition of the best-known varieties of cheese, according to the analysis of various chemists:--