166 Butter Churning. [Sept., 



oxygen alone, therefore, the elaic may be changed into the mar- 

 garic acid. Thus — 



Carbon. Hydrogen. Oxygen. 



To one of elaic acid - - 36 33 3 



Add four of oxygen, - - 4 



And we have - - 36 33 7 



From this take two of car- 

 bonic acid, - - - 2 4 



And margaric acid remains, 34 33 3 



That is to say — if one of liquid elaic acid absorb from the air, 

 or from any other source, four of oxygen, it will, in favorable 

 circumstances, give oiF two of carbonic acid, and become trans- 

 ferred into margaric acid. 



We do not know any probable way by which the converse 

 change of the margaric into the elaic acid can be effected in so 

 simple a manner. The natural process of change, therefore, of 

 the fats of butter, seems to be from the more fluid into the more 

 solid fat. 



It is confirmatory of this view, that the liquid elaic acid is with 

 difficulty obtained in a pure state. Itstenden<;y to absoib oxygen 

 is so great, that by simple exposure to the air it undergoes a rapid 

 alteration. The tendency being thus rapidly to absorb oxygen, 

 the probability is very great that in favorable conditions the more 

 fluid fat of the milk, as it comes from the cow, will be in a great- 

 er or less degree changed into the more solid fat — in other words, 

 that from the same milk under varying circumstances, a butter of 

 greater or less hardness may be obtained, in consequence of such 

 a purely chemical change. 



It is a further confirmation of the view that I have advanced, 

 that gas has occasionally been observed to be givenoff during the 

 operation of churning, and that this gas has been supposed to be 

 carbonic acid.* 



2. Circumstances under which Butter is churned. — In what 

 way do the circumstances under which butter is churned vary? 

 Can such usual variations affect the greater or less absorption of 

 oxygen by the more fluid fat of the milk? 



'J'he churning of milk involves two operations — a violent agi- 

 tation of the particles of the milk among themselves, and an al- 

 ternate exposure of the same particles to the action of the air. 

 The former tends to break the thin coverings of the fat globules, 

 the latter exposes these globules to the oxygen of the atmospheric 



• See Thomson's Animal Chemistry. 



