FATS AND SOAPS 159 



calcium carbonate in one gallon of the water (70,000 grains). 

 To determine the permanent hardness repeat the determination 

 with a second 70 c.c. of the water; but first boil it gently for 

 half an hour to precipitate the carbonates of calcium and mag- 

 nesium, and make up again to 70 c.c. with boiled distilled 

 water. The number of c.cs. of soap solution now required 

 will indicate the degrees of permanent hardness. The difference 

 between the two results gives the temporary hardness. 



Butter. — The cream that rises to the surface of milk consists of minute 

 globules of fat. These aggregate when agitated by churning and form 

 butter. Butter, therefore, consists chiefly of fat, but also contains 8 to 16 

 per cent, of water, and i to 2 per cent, of curd, with a variable quantity of 

 added salt. The fat consists of the glycerides of oleic, palmitic, stearic, 

 and myristic acids (the last in small quantity), together with the glycerides 

 of certain volatile acids soluble in water, the chief of which is butyric acid. 

 Of these combined acids the volatile acids form about 8 per cent. , the oleic 

 acid 36 per cent., and the palmitic, stearic, and myristic acids about 49.5 

 per cent, of the butter fat. The specific gravity of butter fat varies be- 

 tween .910 and .914 at 37.7° C. Animal fats used to adulterate butter, and 

 in the manufacture of oleo-margarine, are devoid of the glycerides of the 

 soluble acids ; and the specific gravity of these being higher than that of 

 olein, palmitin, and stearin, such fats have a lower specific gravity — .903 to 

 .905 at 37.7° C. The purity of butter can therefore be determined by 

 taking the specific gravity. For this purpose the butter is melted, and the 

 liquid fat poured off from the water and curd, and filtered into the specific 

 gravity bottle. The specific gravity is determined at 37.7° C. (100° F.). 

 It is not always possible to detect a small amount of foreign fat in butter by 

 this method, and in this case the purity of the butter is determined by 

 saponifying, acidifying the soap produced, weighing the insoluble acids 

 thrown out of solution, and titrating the aqueous liquid containing the 

 soluble acids with a standard solution of alkali. In this way the proportion 

 of the soluble and volatile acids to the insoluble and non-volatile acids is 

 determined. 



