402 Chittenden and Painter— Casein and its 
filtrate, a portion of the substance precipitable only on addition 
of acetic acid. . 
Of the several preparations of deuterocaseose, those precipitated 
by ammonium sulphate are evidently the only ones perfectly pure. 
Further, it is evident that this substance can be obtained pure only 
by complete removal of all protocaseose from the solution, which 
implies precipitation of a large portion of the deuterocaseose also, 
and then precipitation of the small amount of dentero remaining, by 
saturation of the fluid with ammonium sulphate. D deutero, pre- 
pared in this manner, shows several very marked points of differ- 
ence from protocaseose. In the first place, it is not precipitated in 
an aqueous solution by acetic acid. Further, the addition of potas- 
sium ferrocyanide to a solution acidified with acetic acid gives no 
precipitate whatever. Cupric sulphate and ferric chloride both fail 
to produce any precipitate in an aqueous solution. Pure dentero- 
caseose, as already mentioned, is not precipitated by saturation of 
its aqueous solution with sodium chloride; addition of acetic acid, 
however, to the salt-saturated solution gives a heavy precipitate, 
which represents perhaps half of the deutero, the remainder of 
which is precipitated only by saturation of the fluid with ammonium 
sulphate. It is thus evident that in the precipitation of protocaseose 
from a salt-saturated solution by acetic acid, more or less deuteroca- 
seose will be likewise precipitated, the amount depending probably 
on the concentration of the solution and other minor circumstances. 
Hence, A deutero is unquestionably contaminated with some proto- 
caseose, and on the other hand protocaseose D 3 and 4, and perhaps 
protocaseose C 2, without doubt contain some deuterocaseose. That 
A deutero contains some protocaseose, is evident from the fact that 
it gives a precipitate with cupric sulphate, and further its aqueous 
solution is rendered decidedly turbid by acetic acid. Moreover, the 
protocaseose precipitated by acetic acid, and which may contain 
some deutero, appears to differ in one or two respects from either 
proto or deuterocaseose. Thus, an aqueous solution of the purified 
substance is precipitated like pure protocaseose by acetic acid, but 
the precipitate is only partially soluble in excess of the acid and 
even that requires a large excess. : 
With nitric acid, pure deuterocaseose gives no precipitate, but on 
warming the solution the xanthoprotein reaction comes out strongly. 
Composition of the caseoses and thetr relation to casein. 
In studying the composition of the various caseoses we have been 
hampered by the large percentage of ash invariably present in all of 
