THE TECHNOLOGIST. [Jan. 1, 1865. 



278 ON CHEMISTRY APPLIED TO THE ARTS. 



But as butter rapidly becomes rancid, it is necessary to adopt means to 

 prevent this as much as possible, and the following are the usual 

 methods — viz., working the butter well with water, and then adding 3 

 or 4 per cent, of common salt, or melting the butter at a temperature 

 below 212° ; but- the following method, employed by M. Breon, appears 

 to give general satisfaction. It consists in adding to the butter water 

 containing - 003 of acetic or tartaric acid, and carefully closing the 

 vessels containing it. The rancidity of butter is due to a fermentation 

 generated by the caseine existing in it, which unfolds the fatty matters 

 into their respective acids and glycerine, and as the volatile acids, 

 butyric, caproic, &c.,have a most disagreeable taste and odour, it is these 

 which impart to butter the rank taste. Allow me to add, en passant, that 

 whilst butyric acid possesses a repulsive smell, its ether has a most 

 fragrant odour — viz., that of pineapple, for which it is sold in 

 commerce. 



Curd of Milk or Caseine has, according to Dr. Voelcker, the following 

 composition : — 



Carbon ..... 53-57 



Hydrogen ...".. 7-14 



Nitrogen ..... 1541 



Oxvgen ..... 2203 



Sulphur 1-11 



Phosphorus ..... 074 



1000 



And is easily recognisable by its white fiocculent appearance. It is 

 insipid and inodorous, like albumen, from which it differs in its insolu- 

 bility in water, though it is dissolved by a weak solution of alkali or 

 acid. But what chiefly distinguishes caseine is that it is not coagulated 

 on boiling, and that rennet precipitates it from its solutions. Dr. 

 Voelcker has proved, however, in his researches on cheese, that the 

 commonly-received opinion that rennet coagulates milk by decomposing 

 the lactine into lactic acid is incorrect, for he has coagulated milk while 

 in an alkaline condition, and it is owing to the difference in the action 

 of rennet on albumen and caseine that chemists have been able to detect 

 the presence of ^ to f per cent, of albumen in milk. This important 

 organic substance not only exists in milk, but is also found in small 

 quantities in the blood of some animals, such as the ox, and in a large 

 class of plants, but more especially in the leguminous tribe, such as 

 peas, beans, &c. Caseine is the basis of all cheeses, and when these are 

 made with milk from which the cream has been previously taken the 

 cheese is dry, but when part of the cream has been left the cheese is 

 rich in fatty matters as well as in caseine ; and I may add that 

 the peculiar flavours characterising different cheeses are caused by 

 modifying the conditions of the fermentations which the organic matters 

 undergo. The following researches made bv M. Blondeau illustrate 



