370 PHYSIOLOGICAL CHEMISTRY. 



natural milk containing large quantities of fat has the same 

 specific gravity of 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 in determining 

 the quantity of cream present. 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 LO per cent. Milk which shows a large 

 quantity of cream (15 to 18 per cent.) may fall considerably 

 below 1030 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 "lac- 

 toscopes," 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) fiuid than that from which 

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



One of the lactoscopes has been introduced under the name 

 of pioskop, and consists of a round disk about two and a half 

 inches in diameter, with a shallow disk-like depression in the 

 centre, in which a few drops of milk are placed. This is then 

 covered by a glass disk, transparent in the middle where it rests 

 on the milk, the rim being covered by six radial strips of oil- 

 paint, varying from white to dark gray, and marked with the 

 quality corresponding to it, from "cream" to "very poor milk." 

 The color of the thin layer of milk, as seen through the trans- 

 parent part of the glass plate, corresponds with one of the six 

 color strips, and its quality is thus readily, though riot very 

 accurately, determined. 



The above methods of determining the purity of milk, although 

 answering for ordinary purposes, are absolutely insufficient for 

 scientific purposes or as evidence upon which to base legal pro- 

 ceedings. In such cases a complete analysis, including the 



