W. O. Fenn 281 
The results obtained by this method may be presented under 
the following four headings: (1) The effect of single electrolytes. 
(a) Acids and alkalies; (6) salts. (II) The effect of combina- 
tions of salts with acids and alkalies. (III) The effect of combi- 
nations of salts. (IV) The precipitation of gelatin by mixtures 
of electrolytes without alcohol. Each of these will be presented 
in a separate paper. 
% ALC.TO PPT, 
NaOH 
70 
VISCOSITY 
from 
Schroeder 
50 
30 
J 2 3M 
Fia. 1. Curves showing the effect of NaOH and HCl on the precipita- 
tion of gelatin by alcohol. The ordinates represent the concentrations of 
alcohol in the solution at the point of precipitation, and the abscissze 
the concentrations of HCl and NaOH at that point. The dotted lines 
indicate that no precipitate could be obtained no matter how much alco- 
hol was added. The insert shows von Schroeder’s curves for the viscosity 
of gelatin sols, showing that the alcohol maximum corresponds to a vis- 
cosity maximum. 
a. Acids and Alkalies. 
The presence of actds and alkalies in gelaten hinders the precipt- 
tation by alcohol. With strong acids and alkalies, like NaOH 
and HCl, this effect passes through a maximum. 
The effects of NaOH and HCI are shown in Fig. 1, where the 
concentration of alcohol at the point of precipitation is plotted 
(ordinates) against the concentration of NaOH or HCl at the end- 
