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II. — On the Production of Butter. By Thomas Rowlandson, 

 C.E., F.G.S. 



' Prize Essay. 



Milk — the fluid secreted by females of the class mammalia, for 

 the nourishment of their young — is a white, translucent, aqueous 

 emulsion, the principal components of which are the oily com- 

 pounds called butter, casein or curd, a species of sugar, and 

 certain salts. 



Under the microscope milk appears as a transparent fluid, in 

 which small white globules are diffused, of variable diameters, in 

 the same milk, as well as in that of different animals. These 

 globules collect upon the surface of the milk, when- allowed to 

 remain at rest, or stand, forming the substance known as cream. 

 Some have supposed these to be naked globules of fatty matter, 

 others consider that they are surrounded by a distinct containing 

 membrane. The latter view is, in some degree, rendered probable 

 from the circumstance that they do not coalesce by standing, or 

 when gently heated, nor does ether directly dissolve them ; but 

 when acetic acid is added to milk, it appears to dissolve the 

 containing caseous or albuminous membrane, and the globules 

 then coalesce into drops, Avhicli ether readily takes up. 



The specific gravity of milk varies ; that of the cow is generally 

 about 1 "030. As it is affected by the presence of butter on the 

 one hand, which diminishes, and the casein and salts on the 

 other, which increase its density, it is difficult to ascertain a 

 mean, or to form an estimate of its value by this means ; all 

 lactometers are consequently fallible as indicators of the value of 

 milk. 



According to Berzelius, the specific gravity of skimmed milk 

 is 1 • 033, that of cream 1 • 024, consisting as follows : — 



Skimmed Milk. 



Water 928 '75 



Caseous matter, or curd, with a trace of butter . . 28-00 



Sugar of milk 35-00 



Hydrochlorate and phosphate of potash . . . 1-95 



Lactic acid, acetate of potash, and a trace of lactate of iron 6 ' 00 



Earthy phosphates . . . . . . . 0-30 



1000-00 



Cream. 



Butter 4*5 



Curd ......... S-5 



Whey 92-0 



100-0 



