132 ANIMALS AND THEIR PRODUCTS. 



some contain so little that they do not rise at all. 

 There is, therefore, no doubt that the whole milk con- 

 tains more oil than the cream*; but whether, in actual 

 practice, more of the oil can be separated and made 

 into butter by churning the whole milk, than by 

 churning thfe cream only, is not so clearly decided. 

 Theory would seem to favor the affirmative, but care- 

 ful experiment only can decide. 



238. It may be remarked here, that the oil con- 

 tained in milk is of two kinds, which can be separated 

 by pressure : one, a yellowish, liquid oil, called Oleine; 

 the other, a white, solid substance, somewhat resem- 

 bling tallow, called Margarine. The learner should 

 also bear in mind that oil is a non-nitrogenous sub- 

 stance (CHO), and that curd, or caserne, is one of those 

 nitrogenom substances before spoken of, as containing 

 nitrogen. Now it is a general rule of chemical com- 

 pounds, that those which are composed of but few 

 elements are more permanent in their nature ; and 

 that those which are composed of many are more per- 

 ishable. It is also a well-known fact, that compounds 

 containing nitrogen, when they begin to be decom- 

 posed, become exceedingly offensive. Accordiogly 

 the oil of milk, if entirely separated from other ingre- 

 dients, is very permanent, is not easily decomposed, 

 and does not readily become offensive to the taste or 

 smell ; while curd, containing, as it does, carbon, hy- 

 drogen, oxygen, and nitrogen^ and a little sul2yhur and 

 phosphoriLS — no less than six elements — is most easily 

 decomposed; and when decomposed, it becomes 

 almost: intolerably offensive, and, acting like yeast, it 



