204. REPORT OF THE CHEMIST OF THE 
lutions of neutral salts (potassium chloride and magnesium sul- 
phate). 
4. Solubility of casein in dilute acids——It was necessary first 
to ascertain conditions under which casein forms soluble compounds 
with dilute acids in order to avoid such solution. Evidence of sol- 
ution was shown (1) by viscosity of solution, (2) by behavior of 
solution on adding alkali, such as opalescent or milky appearance 
oy precipitation, (3) by the xanthoproteic reaction, and (4) by de- 
viation between results obtained by conductivity and by titration 
methods. In case of solution, titration results are untrustworthy 
for measuring the amount of free acid in solution because the dis- 
solved proteid neutralizes per se part of the alkali used for titration, 
and also gives up to the alkali any acid with which the proteid may 
have combined. Little or no solution of casein occurs even on sev- 
eral hours’ contact at 0° C. with solutions not stronger than N-500, 
or at 25° C. with solutions not stronger than N-1o000. Degree 
of solution is increased (a) by concentration of acid, (b) by in- 
crease of temperature, and (c) by prolongation of contact. The 
solvent action of the four acids studied was in the following order, 
from the strongest to weakest: hydrochloric, lactic, sulphurie and 
aetic. ‘The rate at which casein dissolves in different acids of the 
same normality is not proportional to the concentration of the Ht 
ions, or to the dissociation, but is disproportionately great for the 
weak organic acids. From solutions of equal strength, the dissolved 
proteid takes up a larger proportion of acid than does the undis- 
solved. 
5. General action of acids and casein without solution.— 
Casein takes up acids from dilute solutions. For example, one 
gram of casein shaken with 100 cc. of N-1000 hydrochloric acid 
for 3 hours, takes from the solution nearly 50 per ct. of the acid. 
The amount of acid thus taken up is not definite and fixed but varies 
(1) with the concentration of the acid, (2) with the duration of 
contact until equilibrium is reached, which requires some hours, 
(3) with the degree of agitation until equilibrium is reached, 
(4) with the temperature, and (5) with the kind of acid. Some 
acid is always taken up, however small the amount of acid used; 
but the acid is never completely removed from the solution, how- 
ever large the proportion of casein present. 
