282 Effects of Electrolytes on Gelatin. I 
point (abscisse). The maximum in the curves corresponds to 
a point of maximum swelling and maximum viscosity. Von 
TABLE I. 
Effect of HCl and NaOH on the Precipitation of Gelatin by Alcohol. 
HCl NaOH 
Concen- | Alcohol | Concentra-| Alcohol | Concentra- ‘Alcohel Concentra-| Alcohol 
tration of to tion of |(byvolume)| tion of tion of (by vol- 
lat | precipi- HCl at at NaOH at bash NaOH at | ume) at 
start. tate. end-point. | end-point. “start. precipitate. end-point. jend-point. 
M CC. M per cent y om ce. M per cent 
12.2 55 WteG 85 | 4.9 No ppt. 
6.1 30 0.85 79 3.26 eS 
3.05 19 0.61 (e PAN Ws 33 0.38 81 
1.52 18 0.32 71 1.45 29 0.26 79 
0.76 19 0.15 (w. 0.96 28 0.17 78 
0.38 25 0.063 1G 0.64 26 0.12 fe 4 
0.19 50 0.018 85 0.32 23 0.064 75 
0.095 |No ppt. 0.16 24 0.032 76 
05048 fi) ae 0.08 30 0.014 79 
O1024 SS eats 0.04 No ppt 
0.012 23 0.0021 16 0.02 SAS 
0.006 9 0.002 57 0.01 16 0.0027 69 
0.003 6 0.0013 47 0.005 8 0.0021 54 
0.0015 4 0.00075 37 0.0025 6 0.0012 47.5 
0.0 3 32 0.00125 5 0.0007 43 
0.000625 4.5 0.00035 41 
| 0.0 3.2 | 0.0 33 
5 ce. of the HCl and NaOH solutions, in the concentrations noted in 
the first columns, were placed in each tube. 1 cc. of 7 per cent gelatin B 
was then added to each. HCl and NaOH are so effective in preventing 
precipitation that the titration with alcohol must be carried on slowly 
in order to allow the precipitate time to form. In order to save time, all 
the tubes were titrated simultaneously. The same number of cc. of alco- 
hol was added to each in turn until precipitation occurred. The experi- 
ments were performed at room temperature. The decrease of precipi- 
tability in high concentrations is due to decomposition of the gelatin. . 
For purposes of plotting, the concentrations of HCl, NaOH, and alcohol 
at the point of precipitation are calculated. These data are plotted in 
Fig. 1. 
Schroeder’s curves for the viscosity of gelatin sols are plotted on 
the insert for comparison.? Their essential similarity to the 
alcohol curves is undoubted. 
2 von Schroeder, P., Z. physikal. Chem., 1903, xlv, 75. 
