450 PHYSIOLOGICAL CHEMISTRY. 



water may be added. In other words, cream may be removed from, 

 and water added to, the same milk and the specific gravity will be 

 unchanged ; or a natural milk containing large quantities of fat has 

 the same specific gravity as a poorer milk to which water has been 

 added. 



These facts show that the lactometer alone is of no value whatever 

 in milk analysis, although it is useful when the quantity of cream 

 has also been determined. This is generally accomplished by the 

 so-called creamometer, a glass tube or glass cylinder about one foot 

 long, half an inch in diameter, and graduated into 100 parts by 

 volume, the being about an inch from the top. The tube is filled 

 with milk to the and set aside for 12 or 18 hours, when the line of 

 demarcation between the cream and the liquid below is ,well defined 

 and may be easily read off. 



The quantity of cream varies from 8 to 20 per cent., but should 

 not fall below 10 per cent. Milk which shows a large quantity of 

 cream (15 to 18 per cent.) may fall considerably below 1.030 in 

 specific gravity, but if there is little cream (8 to 10 per cent.) and 

 the milk shows a low specific gravity, there can be little doubt that 

 it has been tampered with. 



There are a number of other instruments, the so-called " lactoscopes" used for 

 the determination of cream, the operations of which are based on the fact that 

 milk rich in cream is a much more opaque (or more white) fluid than that from 

 which cream has been taken or to which water has been added. 



The above methods of determining the purity of milk, although 

 answering for ordinary purposes, are absolutely insufficient for scien- 

 tific purposes or as evidence upon which to base legal proceedings. 

 In such cases a complete analysis, including the exact determination 

 of total solids and of various constituents, is required. 



Analysis of milk. The total solids are determined by placing a 

 weighed quantity (from 5 to 10 c.c.) of the well-mixed milk in a 

 weighed platinum dish and heating for several hours in a water-bath 

 until no more weight is lost. The loss in weight represents the water, 

 the weight of the residue the total solids. The fat is determined by 

 extracting the solid residue repeatedly with warm ether, filtering this 

 solution through a small filter, which is to be well washed with ether, 

 and evaporating the ethereal solution in a weighed platinum dish. 



Milk-sugar is next determined by treating the residue (from which 

 fat has been extracted) with hot diluted alcohol ; lactose and a few 

 soluble salts enter into solution ; the liquid evaporated to dry ness in 



