W. O. Fenn 287 
factor, CuCl, being more effective than CaCh, and MgCl, less 
effective. The difference between CaCl and MgCl, is largely 
due to the fact that acid increases the effect of CaCl, more than 
that of MgCl, and the gelatin used is slighty acid. Similar 
experiments performed with less acid gelatin show less difference 
(compare CaCl. curves in Figs. 2 and 5). 
TABLE IV. 
Effect of Sodium Salts and Aluminum Sulfate on the Precipitation of Gelatin 
by Alcohol. 
Aleohol Alcohol q 
sch re s piairiisiaes Ala(504)s. 
Concen-. Concen- 
ees S 4 Uh are of - 
of salt. as 32 Sait. ot Sodiun oncen- Alcohol 
2 é 3 acs Na2SOs churanee STONE to precipitate. 
M cc. CC. cc. M ce. CC. M cc. 
2.0 TOS TOSS 1373 4-055 | 4.4 | 0732 Ppt. without 
1.0 10.1 | 9.95}10.7 | 0.25 4.55 |. 6.4 alcohol. 
0.5 9.0 | 9.0 | 9.05) 0.125 cal 8:6" (20°23 4.85 
0:25 Ba0, S20 1s729s)|.0.0625 468.25 | 9.45 1.0.16 yes 
Usi2oue 0.50) 7.00) 6.97190. 0312 | 8.15 } 10.05 | 0.08 5.2 
U20625, | G.15),6.05|.6.2>) 0-0156 | 7.65 |} 10.75 | 0.04 4.95 
0.0 4.4 0.0078 | 5.8 8.95 | 0.02 4,89 
: 0.0039 | 5.1 anon OO 4.75 
3 per cent gelatin B/ 09 .00195| 4.3 | 4.45 | 0.005 5.4 
for 15 hrs. at 26°C. | 9.00097 4.3 | 0.0025 5.2 
0.0 3.9 3.9 | 0.0012 4.8 
4.6 
0.0 | 
ja per cent, gelatm BB |——___ 
15 hrs: at 26°C. 3 per cent gelatin B for 
5 hrs. at 26°C. 
NazSO, and to some extent sodium citrate salt out the gelatin before 
the true end-point is reached. The white stringy precipitate due to salt- 
ing out becomes so opaque that in these curves it is taken as the end-point. 
In (NH,).SO, in Table V it is possible to titrate through to the usual white 
homogeneous precipitate. For other details see Table II. 
It is also evident from the curves in Fig. 2 that MnSQO, and 
CuSO,, which combine bivalent cations with a bivalent anion, 
do not increase the alcohol number at all, but decrease it. This 
cannot be due entirely to the fact, which Nernst!® has men- 
16 Nernst, W., Theoretical Chemistry from the Standpoint of Avoga- 
dro’s Rule and Thermodynamies, London, 3rd edition, 1911, 510. 
