8 MARKET DAIRYING 
it is both acid and alkaline. This double reaction is due 
largely to acid and. alkaline salts and possibly to small 
quantities of organic acids. 
Milk has an average normal specific gravity of 1.032, 
with extremes rarely exceeding 1.029 and 1.033. After 
standing a few moments it loses its homogenous character. 
Evidence of this we have in the “rising of the cream.” 
This is due to the fact that milk is not a perfect solution 
but an emulsion. All of the fat, the larger portion of the 
casein, and part of the ash are in suspension. 
In consistency milk is slightly more viscous than water, 
the viscosity increasing with the decrease in temperature. 
It is also exceedingly sensitive to odors, possessing great 
absorption properties. This teaches the necessity of plac- 
ing milk in clean pure surroundings. 
Chemical Composition. The composition of milk is 
very complex and variable, as will be seen from the fol- 
lowing figures: : 
Average Composition of Normai Milk. A com- 
pilation of figures from various American Ex- 
periment Stations. 
SW ater: svsvevercnsronncertiaiay erahoreoanecen eames 87.1% 
Butler tat: ceideaesscaneawee eee seas 3.9% 
GCaseitiy Asati et ews eaen eee nes 2.9% 
ALI tiene acerocesdee detec Soles seonavaties ovaes avetacoeane 5% 
SUS aT yarns cocaresw ners Sieiivinleinietn tite See cas 4.9% 
IAS Iiceras tn cera ones ore teaches oe ENS 7% 
Pibritt: Aiecee ace eee sees estes Trace 
Galactasé. sis. .s600% Sais bie w'e'e's SiasvOuaveers Trace. 
100.0% 
The great variations in the composition of milk are 
shown by the figures from Koenig, given below: 
