1895-96.] Mr D. F. Harris on Chemistry of Milk. 
77 
tion. Tartaric and citric acids precipitate it in milk, but not in 
pure solution, not even when their powders are boiled with it. 
Carbolic acid fails to precipitate it in either condition. Lactic acid 
when dilute precipitates it in pure solution, but not in milk when 
either dilute or strong. When strong it does not precipitate it 
even in pure solution. This inertness of lactic acid is very remark- 
able when compared with its alleged activity as a precipitant pro- 
duced by fermentation from lactose. 
On the other hand, tannic, benzoic, oxalic, salicylic, and phos- 
phoric acids precipitate caseinogen in both conditions. 
Boracic acid, so far from precipitating it, is a very efficient anti- 
septic ; mixed with it milk appears not to become putrid at the end 
of three months. 
Milk alone would not, therefore, seem to be an antidote for 
picric, carbolic, or boracic acid poisoning. 
With an alkali, e.g., KHO, UaHO, or UH 4 .HO, milk, especially 
if heated, becomes less opalescent, and if further heated some pre- 
cipitate may appear. In a very short time the solution becomes 
yellowish-brown from decomposition and some saponification of the 
fats. Upon neutralisation or acidification an abundant precipitate 
falls. With certain acids, the neutralisation precipitate is dissolved 
in excess of the acid, caseinogen in these circumstances behaving 
like a true alkali-albumin. 
Pure caseinogen treated, e.g., with UH 4 .HO, is “dissolved,” in 
that the solution is clarified ; neutralisation or acidification preci- 
pitates it, and excess of weak acid only slightly dissolves it. 
The Conditions affecting the Coagulation of Caseinogen. 
Various preparations of rennet differ in several respects from one 
another. I used two “essences” : — (1) Duncan, Flockhart & Co.’s, 
a highly acid, glycerine extract of the gastric mucosa of the calf. 
It is not quite lime-free. In details of experiments this is desig- 
nated “A.R.” (acid rennet). (2) Martindale’s “pure essence.” 
This is an UaCl-extract, containing, therefore, chloride of sodium. 
It is by no means lime-free either. It is the “ M.R.” of my notes. 
In some experiments I neutralised it with NH 4 .HO : this is 
“N.R.” 
