FATTY ACIDS. 19 



becomes paler, then blue, and, finally, nearly colourless, while 

 showing a fine green fluorescence. 



By cautiously heating cholesterol with a drop of strong nitric 

 acid and adding ammonia before the product has cooled com- 

 pletely, a yellowish-red coloration is produced. 



If a mixture of 3 measures of concentrated hydrochloric acid 

 and 1 of a solution of ferric chloride be evaporated with a little 

 cholesterol, a reddish-violet coloration changing to blue is pro- 

 duced. By substituting sulphuric acid for hydrochloric acid, 

 a carmine colour is produced, passing gradually to violet, which 

 is changed to scarlet on treatment with ammonia. 



Fatty Acids. 



Acids of the Series, C /( H 2rt+1 COOH. As far as is known, only 

 the normal acids of this series, in which n is an odd number, 

 occur in the fat of milk. 



Butyric Acid, CH 3 CH 2 CH 2 COOH. Grunzweig has proved 

 that the butyric acid of the fat of milk is normal. This acid is 

 a liquid with a characteristic smell, which is specially developed 

 in dilute solution ; the anhydrous acid has a sharp acid smell, 

 the characteristic smell being hardly perceptible. 



The acid solidifies at 19 C. The solidified acid melts at 



2 to + 2 C. according to Linnemann, and at 4-5 to 



2 C. according to Zander. The boiling point is variously 

 stated according to different authorities. Thus 



Linnemann gives ..... 162-3C. 



Lieben and Rossi, 163-2 



Kahlbaum 161-5 



Bruhl, 161-5-162-5 



Zander, 162-3 



The author finds ..... 161-5-162-5 



20 

 The density is given as 0-9587 at -^ by Bruhl, 0-9746 at 



by Zander, and 0-9886 at by Linnemann. 



It is very difficult to prepare the anhydrous acid by distillation 

 alone, the last traces of water being retained with great obstinacy ; 

 dehydrating agents remove this water, and the acid is somewhat 

 hygroscopic. It is soluble in all proportions in water, but is 

 separated as an oily layer on saturating the solution with calcium 

 chloride. It is extracted from aqueous solution by ether. 



From dilute solutions it distils 2-0 times as fast as water i.e., 

 the vapour arising from a dilute solution contains 2-0 times the 

 proportion of butyric acid contained in the solution. Its solu- 

 bility in the mixture of higher fatty acids of milk fat is very small. 



By the action of strong chromic acid at the boiling point it is 

 oxidised to a mixture of carbon dioxide and water, but dilute 



