—_—-- =~ 
ON COLLOID CHEMISTRY AND ITS INDUSTRIAL APPLICATIONS. i 
arc. By this improved method Svedberg succeeded in preparing 
colloidal solutions of all the metals, ineluding the alkali metals. 
Liquid methane, ether and isobutyl alcohol at low temperature were 
especially satisfactory with the metals of the alkalies and the alkaline 
earths. The order of disintegration of some of the metals under 
similar conditions was found to be Fe, Cu, Ag, Al, Ca, Pt, Au, Zn, 
Sn, Cd, Sb, Tl, Bi, Pb, the iron being the least rapidly disintegrated 
and the lead the most rapidly disintegrated. There is no apparent 
relation either with the order of the boiling-points or with the order 
of disintegration by cathode rays or canal rays. 
5. Hlectrochemical Disintegration.—With a lead cathode in caustic 
soda solution, the lead disintegrates when the current density exceeds 
a critical value, and the solution is coloured black like ink, with fine 
particles of metallic lead.®® This is due to the temporary formation 
of a sodium-lead alloy, which then disintegrates in contact with 
water. Similar resultscan be obtained with cathodes of tin, bismuth, 
thallium, arsenic, antimony, and mercury. KE. Miiller® obtained 
colloidal solutions of tellurium with a tellurium cathode. This 
seems to be due to the formation of polytellurides, which break 
down and set free tellurium. In the presence of oxygen there may 
also be an oxidation of a telluride. Fischer®! has obtained metallic 
copper in the solution by using a high current density with a copper 
anode in sulphuric acid. Cuprous sulphate is formed, which breaks 
down to metallic copper and cupric sulphate. This experiment has 
not yet been made to give colloidal copper ; but this could probably 
be done if one were to add a suitable protecting colloid. The 
disintegration of all electrodes by an alternating current when the 
current density is high is undoubtedly due to the temporary formation 
and subsequent breaking down of a hydrogen or metallic alloy. 
Three classes of colloidal solutions have been distinguished, in 
which the stabilisation is due: to adsorbed liquid; to adsorbed 
non-electrolyte, which may be in true solution or may be itself in 
colloidal solution ; and to an adsorbed ion. The last case is the 
easiest one to treat theoretically and is therefore taken up first. So 
long as the particles are all charged positively or all charged nega- 
tively, they will repel each other and will not coalesce. If the charge 
is neutralised or counter-balanced in any way, the particles will 
agglomerate” unless some other factor comes in. If a suspension is 
stabilised by the preferential adsorption of hydrogen ion from 
hydrochloric acid solution, the solution contains free hydrogen ions, 
free chlorine ions, and the adsorbed hydrogen ions which make the 
suspension behave like a cation though with a different migration 
velocity from that of hydrogen. If the suspension is made to adsorb 
an anion in an amount equivalent to the hydrogen ion adsorbed, the 
59 Reed, Jour. Franklin Inst. 139, 283 (1895). 
Bredig and Haber, Ber. deutsche. Chem. Ges. 31, 2741 (1898). 
Haber and Sack, Zeit. Hlektrochemie 8, 245 (1902); Zeit. Anorg. Chem. 34, 286 
1903). 
5 60 ve, Elektrochemie 11, 521, 701 (1905). 
Haber, Ibid. 11, 660, 827 (1905). 
81 Jbid. 9, 507 (1903). 
6 Hardy, Zeit. Phys. Chem., 33, 385 (1900). Burton, Phil. Mag. (6), 12, 472 
(1906) ; 1'7, 583 (1909). 
20895 A4 
