New York AGRICULTURAL EXPERIMENT STATION. 207 
and Pemsel! concluded from the lack of constant combining pro- 
portions that the reaction between proteids and acids was not a | 
true salt formation, but a case of physical distribution of the acid 
between proteid and solvent water. In reaching their conclusions, 
however, they appear to have overlooked the effect of the hydro- 
lysis which is to be expected from salts of weak bases, and the 
weight of evidence inclines entirely towards the view that proteids 
form chemical compounds with acids. 
In studying the action of acids on proteids, various methods have 
been used by different workers in measuring the amount of free 
acid that disappears as such after treatment with proteid. In the 
case of a soluble proteid-acid product, the compound may be pre- 
cipitated and the quantity of acid that is held in the precipitate or 
left in the solution determined by ordinary chemical methods. 
Titration of the solution has been the method usually employed. 
As precipitants, Cohnheim and Spiro and Pemsel used ammonium 
sulphate. Later Cohnheim and Krieger introduced the use of cal- 
cium phospho-tungstate. Erb also employed this method, and his 
results led to the conclusion that proteid-acid salts hydrolyze more 
completely as their concentration increase, a behavior directly op- 
posite to that of known hydrolizible salts. Von Rohrer, however, 
showed that the calcium phospho-tungstate method could not give 
accurate results, because the phospho-tungstic acid, like phosphoric, 
renders accurate titration impossible. He showed that picric 
acid and dipotassium mercuric tetraiodide (K,HglI,) precipitated 
acid albumin containing an unvarying equivalent of acid inde- 
pendent of the excess or kind of acid, also of the temperature, and 
of the precipitant used. He explains this on the ground that while 
an equilibrium exists between the acid-proteid (Alb Cl) and free 
proteid (Alb OH), 
Alb Cl-+- HOH =. AIbOH + HCI 
only the acid-proteid is sufficiently dissociated to react with the pre- 
cipitant. As this is precipitated and the equilibrium disturbed, the 
reaction goes from right to left, forming more Alb Cl, which in turn 
is thrown down, until no proteid is left in solution, the precipitate 
being entirely unhydrolyzed acid-proteid. This method gave the 
* Arch, Physiol. Chem., 26:233. 1898-0. 
