FATS, PHOSPHATIDS, ETC. 85 



agent such as potassium acid sulphate, boric acid or phosphorus 

 pentachloride. Acrolein is easily recognized by its extremely 

 sharp and irritating odor. Since only substances containing glyc- 

 erine give the test, it may be used to distinguish between fats 

 and fatty acids or soaps. 



CHoOH CH 2 



II 

 HOH _2H 2 0-^ CH 



I I 



CH 2 OH CHO 



Acrolein. 



Melting Point. The melting points of the natural fats are 

 not sharp, since natural fats usually are mixtures. They often 

 melt, solidify on further heating, and melt again at a higher 

 temperature. Those fats whose melting points are below or- 

 dinary room temperature are called oils. The melting points 

 of fats in animal tissues are generally below the usual tempera- 

 ture of those tissues, so that the body fats are in a fluid state. 

 The fats of cold blooded animals melt at lower temperatures 

 than those of warm blooded animals. 



Saponification Equivalent. The saponification equivalent is 

 the number of milligrams of potassium hydrate necessary to 

 neutralize the fatty acids produced by the saponification of one 

 gram of fat. The smaller the molecular weight of the acids 

 in the fat, the larger will be the number of molecules in a gram, 

 and the higher the saponification number. Fats made up of 

 fatty acids such as palmitic, stearic and oleic acid such as oleo- 

 margarine have a saponification number around 195. Butter, 

 which contains fatty acids of low molecular weight has a 

 saponification number around 227. These two substances may 

 be distinguished easily in this way. 



Volatile Fatty Acids. Reichert-Meissl Number. This method 

 is used to give evidence of the amount of lower fatty acids in 

 a fat. The fat is hydrolized with alkali, acidified with sul- 

 phuric acid and distilled. The fatty acids of low molecular 

 weight distil over and may be titrated. Those of higher molec- 



