1895-96.] Mr D. F. Harris on Chemistry of Milk. 
81 
used in cheese-making, it becomes like the hardest outside portions 
of a cheese. It has been classified as “ coagulated proteid,” and 
although it is such in origin, yet it departs markedly from the 
characteristics of that group as typified by “ Fibrine.” For instance, 
it is readily soluble in strong acids, e.g ., H 2 S0 4 , and alkalies, e.g ., 
KHO, forming a violet and a pink solution with each respectively. 
This is quite unlike fibrine. Further, casein may be dissolved (to a 
certain extent) in CaH 2 0 2 , from which solution it may be clotted 
by rennet, and this process may be repeated ad injin . — unlike 
fibrine, but like myosin. Ringer has insisted that casein is a 
chemical compound usually of a calcic salt, with the soluble form 
of casein : this I tried to verify by chemical analysis of the whey 
or filtrate from milk clotted by rennet, and milk coagulated by 
acetic acid. The results of one of these analyses are as fol- 
lows : — * 
Total Ash in 50 c.c. Ca 3 2(P0 4 ) per cent, of Ash. 
Acetic acid whey, . *141 grm. 41T3 per cent. 
Rennet whey, . . *231 ,, 32 90 ,, 
From which we see there is less calcic orthophosphate in 50 c.c. of 
rennet whey than there is in 50 c.c. of acetic acid whey — a differ- 
ence which is a measure of the salt that has combined with the 
procasein to form the clot. This also shows that there is some 
chemical difference between the precipitation of caseinogen by 
an acid and the clotting of it by rennet — a difference able to be 
expressed, at least, in terms of the union of calcic phosphate. Some 
call this clot a caseate of calcium. Normally in milk it may be so ; 
but, whatever view we take of its chemical nature, we must not 
forget that artificially we can produce a barium casein or a 
strontium-casein with as great ease as a calcium-casein. Analysis 
also shows that there is less calcic phosphate in rennet whey than 
in the same volume of milk ; again a proof that this salt has 
chemically united with the procasein. 
I believe I have been able to observe a slight rise of temperature 
in milk to which rennet was added over that maintained in a 
specimen of pure milk ; but, without further corroboration of this 
* These analyses were kindly carried out for me by Mr William Lang, 
B.Sc., of the Chemical Department of Glasgow University. 
YOL. XXI. 
F 
