ey REPORTS ON THE STATE OF SCIENCE.—1918. 
REPORT ON PEPTISATION AND PRECIPITATION. 
By Professor WILDER D, BANCROFT, Cornell University. 
Sufficiently small particles will be kept in suspension in a liquid 
by the Brownian movements. Any method which will form small 
particles and will keep them from coalescing will give rise to col- 
loidal solutions. Tentative theories of peptisation have been dis- 
cussed by Lottermoser,! Jordis,? Mecklenburg,? and von Weimarn.* 
If we adopt Freundlich’s view® that adsorption always luwers the 
surface tension, a theory of peptisation follows at once,® because an 
adsorbed film with a low surface tension on the solvent side and a 
high one on the other side will tend to disintegrate or peptise the 
other substance as internal phase. 
When a liquid is adsorbed by a solid, it will tend to peptise it 
and in some cases will do so. Water peptises tannin readily and 
amyl acetate peptises pyroxylin. At higher temperatures the pep- 
tising action increases. Gelatine is peptised by warm and not by 
cold water. Glass is peptised by hot water’ and vulcanised rubber 
by various heated organic liquids,® while fused baths peptise metals.° 
There are a number of cases where mixed solvents will peptise 
a solid much better than either one alone—celluloid nitrate in ether 
and alcohol, caseine in pyridine and water,!° and probably cinchonine 
in chloroform and alcohol, as well as phloretine in ether and water.’? 
The theory of this has not been worked out. Cellulose nitrate swells 
in alcohol and not in ether; but it is not known whether this is 
universal or whether alcohol peptises cellulose nitrate at higher 
temperatures. Zein is also peptised in mixed solvents." 
Relatively little work has been done on direct peptisation by 
means of a dissolved non-electrolyte, but a good deal of stress has 
been laid on the cases where a non-electrolyte prevents the formation 
of a visible precipitate. A concentrated solution of sugar in water 
will prevent the precipitation of calcium silicate, silver chromate, 
and silver chloride ;!° also of lime and of the hydrous oxides of 
copper,” uranium, and iron.'® Invert sugar is about seven times 
as effective as cane sugar in holding up hydrous ferric oxide. 
1 Lottermoser, Jour. prakt. Chem. (2) 68, 341 (1903) ; 72, 39 (1905); 73, 374 
(1906); Zeit. phys. Chem. 62, 371 (1908). 
? Jordis, Van Bemmelen Gedenkboek, 215. 
3 Zeit. anorg. Chem. 74, 260 (1912). 
4 Lehre von den Zustinden der Materie, 1, 60 (1914). 
5 Kapillarchemie, 52, 154 (1909); Patrick, Zeit. phys. Chem. 86, 545 (1914). 
§ Bancroft, Jour. phys. Chem. "7Q, 85 (1916). 
7 Barus, Am. Jour. Sci. (3) 41, 110 (1891); (4) 6, 270 (1898) ; '7, 1 (1899); Pail 
Mag. (5) 4'7, 104, 461 (1899). 
5 Barus, Am. Jour. Sci. (3) 42, 359 (1891). 
* Lorenz, Van Bemmelen Gedenkboek. 395. 
10 Levites, Zeit. Kolloidchemie, 8, 4 (1911). 
1 Oudemannsg, Jour. Chem, Soc. 26, 533 (1873). 
12 Schiff, Zeit. phys. Chem. 23, 355 (1897). 
13 Private Communication from Professor Chamot. 
14 Galeotto and Giampalmo, Zeit. Kolloidehemie, 3, 118 (1908). 
15 Weisberg, Bull. Soc. Chem. Paris (3), 15, 1097 (1896). 
16 Lobry de Bruyn, Ber. deutsch. Chem. Ges. 35, 3079 (1902). 
17 Graham, Jour. Chem. Soc. 15, 253 (1862). 
18 Riffard, Comptes rendus, 97. 1103 (1873). 
