323 
litre. The viscosity of the solution should equal the num- 
ber of grams of sugar taken, if it is pure. The coefficient 
of viscosity for glucose is considerably less than for cane 
sugar, so that asmall quantity added to sugar may be 
shown ,if 300 or 400 grams of the sugar are taken for the 
test. : 
THE VISCOSITY OF MILK. 
The apparatus just described furnishes an expeditious 
and simple means for determining approximately the com- 
position of milk, and is especially applicable when frequent. 
examinations of milk from the same source are required. 
The viscosity of milk exceeds that of water on account. of 
the solids which it contains, and no marked change either 
in amount or composition of the solids is likely to occur in 
milk from the same cow or herd without a corresponding 
change in its viscosity. Especially is this true if the specific 
gravity remains unchanged. 
The testing of milk with this viscometer requires more 
care than when perfect solutions or simple liquids are ex- 
amined. The fatty portion being much lighter than the 
serum, separates rapidly as cream, and unless a sample is 
thoroughly mixed immediately before a determination is 
made, the result wili be erroneous. The most satisfactory 
way of obtaining a homogenous mixture is by gently pour- 
ing the milk from one vessel toanother. Violent shaking 
should be avoided, as it introduces considerable air in small 
bubbles which escape slowly and affect the result. The 
temperature should be accurately taken and if possible ad- 
justed to 20° C. The change in viscosity between 15° and 
25° is for each degree abont 6, increasing as the the tem- 
perature falls; corrections on this basis may be made for a 
difference of one or two degrees. 
Kach of the solid constituents of milk hasan influence 
upon its viscosity. The amount of viscosity caused by one 
per cent. of a solid in solution is termed its coefficient of - 
viscosity; this is different for each of the constituents of 
milk. The ash appears to have very little effect and may 
in general be neglected. Its coefficient of viscosity has not 
been accurately determined. 
Trueblood* has found that the transpiration time of 5 per 
cent solutions of cane and milk sugars are almost identical, 
so that their coefficients of viscosity may be safely taken as 
the same. This owing to the method of calibration is 10. 
The fat offers considerable more resistance than sugar 
and its coefficient of viscosity is not the same in different 
samples of milk; its variation is quite marked in milk from 
different cows and is often considerable in that from the 

* Scientific American Supplement, No. 271. 
