MILK. 431 



Thus purified butter is a white solid substance like tallow. 

 Its yellow colour, when it has it, is owing to the food on which 

 the cow was fed. According to Chevreul, melted butter may 

 be cooled down to 80 before it congeals. The temperature 

 then suddenly rises to 90, and continues at that point till the 

 solidification is completed.* 



100 parts of alcohol of 0.822 dissolves 346 of butter. But- 

 ter is very easily saponified, requiring only 8 parts of potash ley 

 to saponify 20 parts of it. 100 parts of cow's milk butter when 

 thus saponified furnish 88-5 parts of fixed solid oily acids. This 

 acid matter contains 11-85 of glycerin, a little stearic acid, and 

 three volatile oily acids, f 



Butter is composed of three kinds of fatty matter, namely, stea- 

 rin, elain, and a fatty matter from which the three volatile oily 

 acids are formed. To this last substance Chevreul, to whom we 

 owe all the facts here stated, has given the name of butyrin. The 

 relative proportions of these three fatty matters may vary accord- 

 ing to circumstances. This is the reason why butter varies so 

 much in its degree of consistence. Braconnot obtained by ex- 

 pression between 40 and 65 per cent, of stearin. :f According to 

 Chevreul, who separated it by crystallization from its solution in 

 alcohol, it is crystalline, and whiter and more brilliant than stea- 

 rin from ox tallow. It melts at 135. 5 according to Braconnot. 

 According to Chevreul, it melts at 111, and 100 parts of alco- 

 hol of 0-822 dissolve only 1-45 of this stearin. 100 parts of it, 

 when saponified, gave 94-5 of fatty acids fusible at 111, and 7*2 

 of glycerin. 



The elain of butter cannot be completely freed from butyrin, 

 nor the butyrin from elain. Chevreul employed the following 

 method to separate them : Purified butter was kept for a long 

 time between 61 and 66 of temperature. At that temperature 

 the elain and butyrin are liquid, while the solid stearin unites to- 

 gether by degrees, so that the liquid portion may be decanted 

 off. This liquid portion is an oil having the specific gravity of 

 0-922 at 66. 100 parts of boiling alcohol of 0-822 dissolve 6 

 parts, of it. Upon this oil its own bulk of absolute alcohol was 

 poured, and the mixture was left for twenty- four hours, being 

 frequently agitated during that time, and the temperature was 



* Chevreul sur les Corps Gras, p. 273. f 



Ann. de Chim. xciii. 227. 



