206 ELEMENTAKY AGRICULTURAL CHEMISTRY 



and from margarine by its behaviour when heated, say in a 

 test-tube or basin, over a flame. Pure butter ** boils" quietly, 

 but with much frothing or foaming, while *' renovated " butter 

 and margarine bump and splutter violently, but do not froth. 



The chief reliable chemical difference between genuine butter 

 and margarine is in the proportion of volatile fatty acids 

 present. 



Butter-milk varies in composition ; in general it resembles 

 skimmed milk, but is usually sour. It contains from 0'3 to 

 3*5 per cent, of fat, 4 to 5 per cent, of sugar, 3 to 4 per cent, 

 of albuminoids, and 0*7 to 0'8 of ash. It finds a limited use 

 in the kitchen, but the greater part is employed as food for 

 pigs. 



Condensed Milk and Milk Powder.— Though the prepa- 

 ration of condensed milk forms no part of the work of the farm 

 or dairy, it may be of interest to explain briefly the character 

 and method of preparation of this and similar products. 



Condensed milk is prepared by boiling milk in vacuum pans 

 until its volume is diminished to about one-third or one-fourth 

 of the original. In many brands cane sugar is added in large 

 proportion, whereby the product keeps better, even after the 

 tins are opened. In other brands, often known as "evapo- 

 rated cream,"* no cane sugar is added. The composition of 

 such products varies considerably, the fat especially being 

 liable to great fluctuation. The following analyses may be 

 taken as typical : 



Un- 

 Sweetened, sweetened. 



Water . 25-7 717 



Fat 10-7 8-1 



Proteids 8-5 87 



Milk sugar 11-9 9-9 



Cane sugar 41*9 — 



Ash _2;3 1-6 



1000 100-0 



* The term '* cream " cannot now be legallj^ uged for such products. 



