22 



THE FAT OF MILK. 



melting at 69-2 (Heintz) or 68-5 (Hehner and Mitchell) to a 

 colourless liquid, which on cooling solidifies to a crystalline 

 whitish mass. Under 100 mm. pressure it boils at 291 C. It 

 cannot be distilled under the atmospheric pressure without 

 decomposition. 



Hehner and Mitchell have shown that at C. a saturated 

 solution in alcohol of 0-8183 specific gravity contains from 

 0-142 to 0-158 gramme per 100 c.c. Absolute alcohol dissolves 

 about 2-5 grammes per 100 c.c. 



The salts of stearic acid are, with the exception of those of the 

 alkali metals (soaps), insoluble in water and almost insoluble in 

 alcohol. The salts of palmitic acid resemble them very much. 

 The most marked difference between these two acids is the 

 difference of solubility of the magnesium salt ; that of stearic 

 acid is practically insoluble in cold alcohol, while that of palmitic 

 acid possesses a slight, but appreciable, solubility ; the presence 

 of magnesium palmitate causes, however, appreciable solubility 

 of magnesium stearate. 



All salts of stearic acid (and palmitic acid) are partly decom- 

 posed by water into basic and acid salts ; the salts of the alkali 

 metals (soaps) cannot be dissolved without becoming appreciably 

 alkaline. They are, however, soluble in hot alcohol without 

 decomposition, forming solutions which gelatinise on cooling. 



Soaps of stearic and palmitic acids are quite insoluble in 12 per 

 cent, solution of sodium chloride. 



General Properties of Acids of the Series, CH 2n+1 COOH. 

 The following Table (VI.) gives a summary of the leading pro- 

 perties of these acids : 



TABLE VI. PROPERTIES OF THE ACIDS OF SERIES 



