A Comprehensive Treatise on Inorganic and Theoretical Chemistry

PLATINUM 57
hydrogen is oxidized to "water. G. Bredig and R. Muller von Berneck studied the
catalytic decomposition of hydrogen dioxide by colloidal platinum ; the activity
diminishes with increasing proportions of protective colloid which may be present.
Thus, J. Groh found the effect of increasing the percentage proportion of gelatin
on the relative times required to decompose 50 per cent, of hydrogen peroxide :
Qelatin . . . . . 0-000 0-001 0010 0-050 O-1OO
Time for decomposition . . 1OO 437 460 620 983
According to G. Bredig and IC. Ikeda, and T. S. Price and J. A. N. Friend, the
activity of the colloid is decreased by hydrogen sulphide or cyanide which are
metaphorically said to poison the reaction. C. J. Farmer and F. Parker observed
that the activity of the colloid is increased by a short exposure to ultra-violet light,
but is decreased with a long exposure until it finally ceases as a black, flocculent
precipitate is formed. T. S. Price and J. A. N. Friend observed that the presence
of colloidal platinum favours the reaction between hydrogen dioxide and permonosulphuric
acid ; and J. A. N. Friend, the reaction between hydrogen dioxide and
potassium persulphate. G. L. Clark studied the subject.
R. Bars, R. Fiirth, H. P. Walmsley, and Ti. Hamburger studied the aerosols
of platinum.
O. Bobertag and co-workers found that the metal in colloidal soln. is flocculated
by rapid cooling. G. Bredig's colloidal soln. is flocculated when cooled to —70° ; and
C. 3. Farmer and F. Parker noticed that the metal is flocculated by a prolonged
exposure to ultra-violet light ; and M. Annetts noted that the colloid becomes less
stable on exposure to cathode rays. P. B. Ganguly and N. R. Dhar, and E. B. Spear
and co-workers studied the subject. E. Muller noted the rapid precipitation of the
metal by a few drops of hydrochloric acid. H. Freundlich studied the coagulation
of the soln. by electrolytes. A hydrosol, with 0-7 millimol of platinum per litre, is
coagulated by soln. of sodium chloride with 2-5 millimol per litre ; potassium chloride,
2-2 ; silver nitrate, 0-22 ; sulphuric acid, 0*12 ; sodium hydroxide, 1-3O ; barium
chloride, 0-058 ; uranyl nitrate, 0-065 ; lead nitrate, O-Oll ; barium hydroxide,
0-058 ; and aluminium sulphate, 0-007. S. W. Pennycuick studied the exchange of
ions at the surface of colloidal platinum. W. Biltz found that a trace of ferric,
aluminium, cerium, zirconium, or chromium hydroxide precipitates the colloidal
platinum from 1 or 2 c.c. of the sol. N. Pappada found that a 4 per cent. soln. of
mercuric chloride does not precipitate the colloidal soln. unless it bo warmed ; soln.
of potassium cyanide or hydrocyanic acid change colloidal platinum chemically ;
there is also a chemical reaction with the halogens—e.g. chlorine or iodine ; 0-12Vsoln.
of non-ionized, organic substances—e.g. methyl or ethyl alcohol, glucose, and
saccharose—coagulate the sol, but N- and more cone. soln. do not do so ; 2 c.c.
of 0-liV-soln. of hydrochloric, nitric, and sulphuric acids coagulate the sol, likewise
also with 1 c.c. of 2V-CsCl ; 1-5 c.c. of iV-RbCl—incompletely, and likewise so with
2V-KC1, 2V-NaCl, and N-IACl ; coagulation occurs with 3 c.c. of 22V-KC1 ; 1 c.c.
of 012V-BaCl2, 0-IiV-SrCl2, and 0-IiV-CaCl2 ; and with 5 drops of 0-12V-Al2(SO4)3,
and 0-12V-Cr2(SO4J3 ; no coagulation occurred with OliV-soln. of CsCl, RbCl,
KCl, NaCl, or LiCl, or with the corresponding bromides, iodides, sulphates, or
nitrates. The coagulation of the sols was studied by S. W. Pennycuick and
R. J. Best, A. Voet, P. C. L. Thorne and co-workers, W. D. Bancroft, Wo. Ostwald,
and A. Ivanitzkaja and co-workers. E. B. Spear and K. D. Kahn observed that
colloidal soln. of platinum are coagulated by metal plates ; and M. Annetts, by
cathode rays. The plates are more active if roughened. The order of decreasing
activity is : zinc, steel, nickel, tin, and copper. A. de Gregorio y Rocasolano
studied the ageing of the sol. Y. Shibata and H. Kaneko studied influence of the
sol on the rate of oxidation of pyrogallol.