304 PHYSIOLOGICAL CHEMISTRY. 



acid. The non-volatile fat consists of -f^ to -fy olein, and the re- 

 mainder of a mixture of palmitin and stearin. 



The quantity of volatile fatty acids in butter-fat is of great practical im- 

 portance in the methods for detecting the presence of foreign fats in butter. 

 This detection is performed generally according to REICHEKT'S process based 

 on HEHNER and ANGELL'S method. The fat is saponified with alcoholic 

 potash and the alcohol evaporated. The soaps are dissolved in water, and then 

 distilled with an excess of phosphoric acid. The quantity of volatile fatty 

 acids in the distillate is determined by titration with deci-normal alkali. With 

 butter of proper composition 2.5 grms. should yield a distillate requiring 

 14-13 cc. for neutralization, and at least not less than 12 cc. of the deci-normal 

 alkali. In proportion as the butter contains a greater quantity of foreign fats 

 the quantity of alkali required becomes smaller. 



The milk-plasma, or that fluid in which the fat-globules are sus- 

 pended, contains at least three different albuminous bodies, casein, 

 lactoglobulin, and lactalbumin, and two carbohydrates, of which only 

 one, the milk-sugar, is of great importance. The milk-plasma also 

 contains extractive bodies, traces of urea, creatin, creatinin, liypo- 

 xantliin (?), lecithin, cholesterin, about 1 p. m. citric acid (SOXHLET 

 and HENKEL) ; a still greater amount according to SOLDNER, and 

 lastly also mineral bodies and gases. 



Casein. This protein substance, which thus far has been de- 

 tected positively in milk, belongs to the nucleoalbumins, and differs 

 from the albuminates by its containing phosphorus and by its be- 

 havior with the rennet enzyme. Casein from cow's milk has the 

 following composition: C 53.0, H 7.0, N 15.7, S 0.8, P 0.85, and 

 22.65 per cent. Its specific rotation is, according to HOPPE- 

 SEYLER somewhat variable ; in neutral solution it is a(D) = 80. 

 The question whether the casein from different varieties of milk is 

 identical or if there are several different caseins has not been posi- 

 tively determined. 



Casein, when dry, appears like a fine white powder which, after 

 heating to 100 C. or somewhat above, shows the properties and 

 solubilities of freshly-precipitated, still-moist casein. Casein is only 

 slightly soluble in water or in neutral-salt solutions. It acts like a 

 rather strong acid, dissolves readily in water on the addition of very 

 little alkali, forming a neutral or acid liquid, and lastly it dissolves 

 in water in the presence of calcium carbonate, from which it expels 

 the carbon dioxide. If casein is dissolved in lime-water and this 

 solution treated with very dilute phosphoric acid until it is neutral 



