W. O. Fenn 289 
tioned, that such salts are comparatively little dissociated. If 
_the degree of dissociation were the sole explanation, one would 
expect CuSO, to have less effect than CuCk, but not the oppo- 
site effect. In some cases such salts do cause a slight increase 
in the alcohol number in low concentrations, as for example in 
the curve for MgSO, in Fig. 3 and for Al, (SO,)3 in Fig. 4. FeSO, 
CC. ALC. TO ppT, 
arere = AlCl 
¢ 
‘ 
| 
' 
' 
20 ees CuCl. 
uf 
CaClz 
MgCl? 
10-4 NaCl 
MnSO: 
eo 
CuSO: 
0 ie 4 .6 8 1.0 
Fia. 2. The ordinates represent the number of cc. of alcohol required 
to produce an opaque precipitate in 5 cc. of the salt-gelatin mixture; 7.e., 
the alcohol numbers. The abscissze represent the'concentrations of the 
various salts in the gelatin before titration with alcohol. The effect of 
the salts increases with the valence of the cation. The dotted lines indi- 
cate that no precipitate could be obtained in those concentrations of: 
AICl; and CuCl... Qualitative tests indicate that the AlCl; curve subse- 
quently comes down a little, like the CuCl, curve. 
also shows a slight increase in the alcohol number in low con- 
centrations. 
As proof of the fact that the alcohol number gives a true 
indication of the effect of salts upon the physical properties of 
gelatin (in spite of the ‘possibility of repression of ionization of 
the salts by the alcohol or other interaction) may be mentioned 
the fact that gelatin sets more readily in solutions of such salts 
as MnSO,, etc., than in water or solutions of salts with one or 
