228 REPORT OF THE CHEMIST OF THE 
Explanation of Fig. 6.— The results given in Table IV are ex- 
pressed in the form of curves in Fig. 6, in which the curves marked 
“Cond.” and having points marked “ x ” express results obtained 
by the conductivity method, while the curves marked “ Titr.” and 
having points marked “o” express results obtained by the titration 
method. 
The numbers associated with the points x and 0 express approxi- 
mate degrees of solution of casein by acid, as indicated below: 
No. Appearance Color Mgs. casein in 
denoting of filtrate on produced by 10cc. of test 
degree of addition xanthoproteic solution corre- 
solution. of alkali. reaction. sponding to color. 
Oe clear none Oo to 0.5 
oy slightly opalescent slightly yellow 0.6 to 09 
aes moderately opalescent moderately yellow 1.0 to 3.0 
othe turbid, milky deep yellow 4.0 to 6.0 
Avs Opaque, some precip. orange 7.0 to 10.0 
nee heavy precip. dark orange 10.0 or more 
5+.. heavy precip. dark orange larger amounts 
The figures in the last column were obtained in the following 
manner: We dissolved 0.5 gram of casein in nitric acid and diluted 
to 500 cc., each cc. containing I mg. of proteid. Different amounts 
of this solution were diluted to 10 cc. each and tested by the xantho- 
proteic reaction. The same system of numbers will be uniformly 
employed hereafter to express approximate degree of solution. 
In Fig. 6 it will be seen that at o° C. there is comparatively 
slight solution of casein and the results obtained by the two 
methods, conductivity and titration, coincide. At 25° C., solution 
becomes marked and the abnormally low curve after the first five 
minutes furnished by titration results is strikingly apparent. At 
45° C., the effect of solution is still more evident. In 15 minutes 
the amount of dissolved casein makes the acidity of the filtrate 
actually greater than that of the original N-125 acid used. 
The results embodied in Table IV and in Fig. 6 are summarized 
as follows: 
(1) Casein takes up hydrochloric acid from solution. At 0° C., 
I gram of casein takes up from I00 cc. of N-125 HCl, without 
appreciable solution, the acid in about 50 cc., which is equivalent to 
