204 REPORT OF THE CHEMIST OF THE 
Regarding the fourth point, it was found that in all cases the 
fundamental principle was complied with: The amounts of acid 
taken up per gram of casein at equilibrium depend upon the final con- 
centrations of the solutions. In the cases of hydrochloric, lactic, 
__concentration acid in casein 
~ concentration acid in water 
stant. This, acording to van Bemmelen, may occur when solutions 
are dilute and adsorptive power weak. While the adsorptive power, 
particularly in the case of hydrochloric acid, is not weak, the so- 
lutions were very dilute. In the case of sulphuric acid, where 

. : C1 : 
and acetic acid, = is nearly con- 
: . Sh . . . 
adsorption is much stronger, the ratio  ilcreases with the dilution, 
2 
in accordance with the usual behavior of adsorptions, and the in- 
° . . cP 
crease occurs in accordance with the exponential formula, Brats , 
2 
which has been found to hold in a large proportion of adsorptions, 
p being 1.95 in this case (p.255). If p be taken nearly equal to 
unity, the same formula holds for the other acids. 
In velocity, the reaction, agreeing with van Bemmelen’s fifth 
criterion, begins with great speed, and becomes slow as equilibrium 
is approached. Particularly when the mixtures of casein and acid 
are subjected to constant agitation so that the casein does not have 
to wait for acid to reach it by diffusion, the initial velocity was enor- 
mous, the curves being nearly parallel to the ordinate axis for some 
distance. Negative acceleration is, of course, observed in reactions 
in general as they approach equilibrium, so that no great force is 
to be attributed to this characteristic for the purpose of classifying 
the reaction, although the enormous initial velocity is not usually 
observed in intermolecular reactions requiring considerable time for 
completion. The great velocity with which acid is extracted by 
water from the insoluble acid-casein furnishes a marked contrast 
_ to the stability of the precipitated acid albumin of von Rohrer, an 
apparently true chemical compound, which could be washed with 
water without changing materially its acid content. 
The fact that the equilibrium can be approached from both sides 
has been shown in the cases of both hydrochloric and sulphuric acids. 
As shown in Fig. 20, the curves obtained in the manner indicated 
by Ostwald are similar to the hyperbola. 
