1895 - 96 .] Mr D. F. Harris on Chemistry of Milk. 
87 
fresh milk yields a blue colour with tincture of guaiac, while boiled 
milk does not. 
I am unable to substantiate the statement of authors that boiled 
milk is “ far more difficult to coagulate than unboiled milk.” 
The clot in boiled milk so entirely fills the tube like a jelly, and 
separates from its whey so slowly, that unless the tube be examined 
very closely, and by inverting it from time to time, the time of the 
formation of the clot may easily be missed. 
By “ difficult,” I presume, “ takes a longer time” is meant, but I 
cannot find that the rennet clot occupies any longer time than in 
ordinary milk to do its work, whether it be added to cold milk 
previously boiled or to warm milk previously boiled. Authors 
state that this “ difficulty ” is due to some of the calcic phosphate 
having become insoluble. I can find none of it upon prolonged 
centrifugalisation of boiled milk. 
The fat of milk may be very strikingly shown by adding to a 
large vessel of milk -Jth or so of its volume of a 1 % sol. of osmic 
acid. The mixture in about half an hour will have become jet 
black, and does not purify within a year. 
The Wheys, Dialysates, and Filtrates. 
In rennet whey there is some caseinogen, for there are yet many 
particles. It may be precipitated by heating the whey with 
CaCk + and a m. or two of phosphoric acid, and it may be clotted 
by A.R. + Cacl 2 + phos. acid, the filtrate from which yields a pro- 
teid, but is perfectly free from particles. 
Rennet whey treated with acetic acid gives a precipitate quite 
indistinguishable microscopically from any of the acid-precipitates 
of caseinogen. 
The original clotting had therefore not comprised all the 
caseinogen. 
Pressure whey (through a Berkefeld diatomaceous filter) has 
no particles, and will not clot. It has a proteid. It is faintly 
acid. 
The filtrate ( icithoui exhaustion) through a clay filter has no 
proteid. ( Egg alb. does not go through the pressure filter.) 
All these wheys, including the acetic acid whey , have lactose 
