XLI. The properties of fats. 



/. Materials. Olive oil; cream; butter; beef tallow; lard; 



adipose tissue; cotton seed oil. 

 2. Experiments and Observations. 



(1) The osmic acid test. Place in test tubes a small 

 amount of each of the above food stuffs; add to each a 

 few cubic centimeters of osmic acid. A characteristic 

 reaction takes place, the result of which is a deep 

 brown coloration of the fat. If the conditions are 

 favorable the stain deepens into a sepia black. The 

 cream and the adipose tissue have proteid admixtures; 

 note the variation of the reaction. 



(2) The solubility of fats and oils. Prepare three tubes 

 each of olive oil, of cream, and of tallow; treat each 

 material with absolute alcohol, with ether and with 

 chloroform. It will be found that all of these re- 

 agents are solvents of fats and oils. The alcohol, 

 however, dissolves very much more of the oil or fat 

 when warm than when cold, as may be demonstrated 

 by making the alcoholic solution with the tube im- 

 mersed in boiling water; after the alcohol seems to 

 have reached the limit of solution at that temperature, 

 immerse the tube in cold water. A large part of the 

 dissolved oil instantly separates out, but will readily 

 redissolve on again immersing the tube in the boiling 

 water. 



(3) The saponification of fats and oils. 



(a} To about 2 c. c. of olive oil in a test tube add 1-2 



* volumes of a 25% solution of sodic hydrate. Shake 



the mixture vigorously; it is evident that a chemical 



reaction is in progress. The fat is undergoing the 



182 



