10 PHYSIOLOGICAL AND PATHOLOGICAL CHEMISTRY. 



is free from calcium or magnesium phosphate. 1 We deter- 

 mine this by adding ammonia to the rest of the solution. It 

 must remain clear. 



4. Butter-fat (D). 



The butter-fat is saponified. All heating and evaporating 

 in this section is to be done on the water-bath. Put 5 g. of 

 caustic potash into a flask, add 5 cc. of water, and dissolve 

 the potash by warming. Then melt the butter-fat and pour 

 it into the flask. Wash the dish with about 50 cc. of 90 per 

 cent, alcohol, add the alcohol to the flask, and heat the mix- 

 ture, with constant shaking, until it becomes homogeneous. 

 The fat is thus split up into fatty acids and glycerin, saponi- 

 fied. In order to determine whether the saponification is 

 complete, pour a small portion of the mixture into a little 

 water; it must form a clear solution or one which becomes 

 clear on gently warming. If it does not do this the mixture 

 must be again heated. When the saponification is completed 

 pour the contents of the flask into an evaporating-dish, drive 

 off the alcohol by heating (water-bath), and when cold acidify 

 with 30 cc. of dilute sulphuric acid. The fatty acids separate 

 in the form of an oil, while at the same time the odor of butyric 

 acid becomes perceptible, due to the presence of butyrin in 

 the milk-fat. This butyrin is characteristic of milk-fat. It 

 is only found in this substance. 



The more detailed investigation of fat and the fatty acids 

 will be taken up in the chapter on " Subcutaneous Adipose 

 Tissue." 



5. Milk-sugar, C 12 H 22 O n +H 2 0. 



The milk-sugar (G) is separated from the mother-liquor 

 by draining and pressing between filter-paper and is recrys- 



1 Alkali phosphates could not be present owing to the previous treat- 

 ment. 



