6 REPORTS ON THE STATE OF SCIENCE.—1918. 
be filtered several times through filter-paper, the water will finally 
run through clear, and the carbon black will be held back by the 
filter-paper. Ifa soap solution be poured on the filter, a black filtrate 
is obtained and the filter-paper is no longer black. All the carbon 
black has passed through the filter paper. The same thing can be 
done with rouge, except that a red filtrate is obtained instead of a 
black one. At first sight it seems that though the soap must have 
broken up the carbon or the rouge into finer particles, which then 
passed through the filter, but this is probably not so. The filter- 
paper is porous enough at first to let through the particles of carbon 
or rouge, as is shown by the fact that some of the suspended matter 
does pass through the filter at first. The cellulose adsorbs the carbon - 
black or the rouge, and this clogs the filter to such an extent that the 
pores are not large enough to let the remaining particles through. 
The soap removes the rouge or the carbon black from the paper 
because it adsorbs these substances more strongly, and everything, 
therefore, goes through the paper. That this is the true explanation 
can be shown in two ways. In the first place, the experiment does 
not succeed if the rouge or the carbon is two coarse. In the second 
place, Spring showed that we are dealing with an adsorption of 
carbon black by filter-paper. If the black filter-paper be reversed 
and washed with water, the water removes only the black which is 
not in immediate contact with the paper. 
3. Mechanical Disintegration.—If a solid be ground sufficiently 
fine, it will necessarily form a colloidal solution for atime. This 
has been done experimentally by Wegelin® in the case of a number 
of metals. The addition of gelatin makes it easier to disintegrate 
ductile metals. Since a finely divided solid is more soluble, it is 
possible that it may go into solution and then precipitate in another 
form. This seems to happen with quartz. When reduced to an 
impalpable powder by long grinding, quartz can be converted into 
colloidal hydrous silicic acid merely by boiling with water.* 
4. Electrical Disintegration—When a direct current are is 
formed under water between two wires, the metal is disintegrated and 
colloidal solutions of platinum, iridium, palladium, gold, silver, and 
cadmium may be obtained in this way.” Satisfactory conditions are 
obtained with 30 to 40 volts and 5 to 10 amperes. A trace of alkali 
in the water causes formation of finer particles, presumably owing 
to the stabilising effect of the hydroxyl ion. The disintegration is 
chiefly at the cathode. 
The method is not satisfactory with organic liquids, because two 
much decomposition of the liquids takes place. Svedberg found 
empirically that this decomposition could be decreased very much 
if the current density were made as small as possible.*® He there- 
fore used an oscillatory discharge from an induction coil with a 
condenser in parallel or in series. The best results are obtained 
with large capacity, small self-induction, low resistance, and short 
55 Zeit. Kolloidchemie, 14, 65 (1914). 
56 Desch, The Chemistry and Testing of Cement, 58 (1911). 
7 Bredig, Zeit. Hlektrochemie, 4, 514 (1898) ; Zeit. Phys. Chem. 31, 258 (1899). 
58 Svedberg, 424, 
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