434 TRAXSACTIOyS OF THE AmERICAX IXSTITUTE. 



Composition of Milk. 

 Fresh milk has l^een frequently analyized by chemists, -with 

 somewhat varying results, due, it may be presumed, to differences in 

 the feeding and general thrift of the animals. Thus, the proportion 

 of casein or cheesy matter, is from three and one-fifth to four and one- 

 half per cent ; of butter, from three and one-eighth to four and one-tenth 

 per cent ; of milk sugar, or lactine, four and three-fourth to five and 

 one-tenth per cent ; of saline matter, from one-fifth to three-fifths 

 of one per cent, and of water about eighty -seven per cent. Each one 

 of these constituents plajs an important part in the chemical changes 

 that take place in the milk preliminary to and during the formation of 

 the butter. The analysis of milk to determine the relative proportions 

 of its constituent parts is a comparatively simple matter to the 

 chemist, and, being capable of more lucid explanation than many 

 other processes of a similar nature, a brief sketch of a good method 

 may not be without interest to those who like to understand some- 

 thing of the means by which the facts of practical science are ascer- 

 tained. The portion of milk to be analyzed is carefully weighed, 

 after which a few drops of acetic acid, the same as the acid of vinegar 

 is added to it. This will cause coagulation, and the vessel contain- 

 ing the milk should then be set in an other vessel filled with boiling 

 water, and kept hot until all the liquid in the inner or milk-holding 

 vessel is evaporated. If we now weigh the dry residuum of the 

 milk, and subtract the weight from that of the original quantity, 

 we obtain the weight of water contained therein. The solid mass, or 

 residuum is then taken and digested for a length of time in ether 

 which dissolves out the butter. The ethereal solution is heated to 

 its boiling point, is filtered through porous paper, and evaporated to 

 dryness, thus leaving the butter as a residue, which may then be 

 weighed. The butter will of course have its peculiar color, which 

 will be found sometimes darker, sometimes lighter, according to the 

 food on which the animal has fed. 



Having thus ascertained the proportions of water and of the butter, 

 it is next in order to determine those of the casein, the milk-sugar, 

 and tlie saline matter. To do this, the surplus left on the filter 

 after filtering the ethereal solution above mentioned, is washed with 

 hot water. This dissolves the sugar and a part of the salts. The 

 aqueous solution thus obtained is separated by filtration, evaporated 

 to dryness, and the product is weighed. The latter is then burned, 

 and the weight of tlie ash, composed of mineral salts, is subtracted 



