NATURE OF DEPOSIT OBTAINED FROM MILK. usr 
lactose, the value of the depression of the freezing point 
for the concentration of lactose in milk is therefore — 0°225°. 
When 0°17% of the lactose in milk breaks up into lactic 
acid the number of particles in solution is increased by 
three times that amount (neglecting the ionisation of the 
lactic acid) since for each molecule of lactose which dis- 
appears, four molecules of lactic acid are formed. The 
breaking up of this fraction of the lactose should therefore 
cause an increase of the depression of the freezing point 
due to this substance of 0°51%, that is, from 0°225° to 
—0°2263°. Hach additional cc. of N/10 alkali required to 
neutralise 100 cc. of milk undergoing souring should there- 
fore correspond to an increase of the depression of the 
freezing point of 0°0013°. This value is a maximal figure, 
as in calculating it we have assumed that the whole of the 
lactose which breaks up forms lactic acid, actually, how- 
ever, some of the lactose breaks up in other ways. 
The acidities of samples of the milks being spun in the 
centrifuge were therefore determined at the beginning and 
at the end of the spinning to ascertain whether the ten- 
dency of the depression of the freezing point to increase 
might be attributed to an increase of the acidity of the 
milk. The samples for the determination of the acidity 
were kept under the same conditions as those being spun 
in the centrifuge. The acidities were determined by titra- 
ting 25 cc. of the undiluted milk, containing 2 cc. of 0°57 
phenolphthalein as indicator, with N/10 NaOH to the first 
distinct pink colouration. The acidities shown in the 
table are expressed as the number of cc. of N/10 alkali 
required to neutralise 100 cc. of milk. The greatest increase 
of acidity occurring during the course of the spinning is 
seen to be 1 cc. of N/10 alkali in 100 cc. of milk, and as 
this corresponds to an increase of only 0°0013° in the lower- 
ing of the freezing point it may be said that the alteration 
