A Comprehensive Treatise on Inorganic and Theoretical Chemistry

208 INORGANIC AND THEORETICAL CHEMISTRY
and H. C. Bennett said that amalgams, not mercury, alone " wet " the surface of
platinum in consequence of their surface tension. E. Englisch observed that mercuryattacks
platinum at 400° ; and C. Hockin and H. A. Taylor, that an amalgam is
formed when red-hot platinum is plunged into mercury. F. E. Carter said that
sodium amalgam attacks platinum, and there is a process for removing platinum
from its crushed ore which is based on this reaction.
P. Casamajor observed that the union of platinum with mercury is favoured by
contact with zinc ; and J. S. C. Schweigger, that the amalgamation is hastened
by galvanic action. R. Abegg and H. S. Hatfield, V. Borelli, W. IJ. Hardin, and
T. WiIm noted the formation of amalgams when platinum is electrodeposited on a
mercury cathode. W. W. Mather obtained the amalgam by heating platinic
chloroiodide with mercury in a sealed tube. According to J. Schumann, and
W. Kettembeil, platinum is best amalgamated by contact with alkali amalgams.
A. C. Christomanos used ammonium amalgam. J. P. Joule, M. Tarugi, and
O. Loew obtained amalgams by allowing mercury to stand in contact with hydrochloroplatinic
acid for a long time ; F. Mylius and O. Fromm, and A. Hilgar and
E. von Raumer, by the action of mercury on soln. of platinum salts ; R. Bottger,
and M. Tarugi, by the action of sodium amalgam on ammonium chloroplatinate,
and, according to O. Hockin and H. A. Taylor, on other platinum salts ;
H. St. C. Deville and H. Debray, by the action on platinum of a soln. of mercuric
cyanide mixed with a little potassium cyanide ; G. McP. Smith, by the action of
platinum on a cone. soln. of potassium mercuric cyanide ; and M. Tarugi, by
reducing a mixed soln. of platinic and mercuric chlorides with magnesium, or
hydrazine.
C. Paal and B.C. Auerswald, and E. C. Auerswald prepared colloidal platinum
amalgam by using sodium protalbinate or lysalbinate as protective colloids, when
mercury acts on a platinum hydrosol, by the reduction of a mixture of platinum
hydrosol and mercuric oxide hydrosol, by reducing a mixed soln. of hydrochloroplatinic
acid and mercuric chloride, and by mixing colloidal soln. of mercury and
platinum. The catalytic action of the colloid on hydrogen dioxide, and electrolytic
gas ; and also the oxidation of carbon monoxide ; and the reduction of nitrobenzene,
have been studied.
The amalgam may appear as a viscid mass, which when heated boils up, loses
its mercury, and leaves behind a finely-divided, black powder, or a grey, coherent
mass of mercury. If pressure is applied during the ignition, A. von Mussin-Puschkin
said that the product is fit for working into malleable platinum. E. Melly, and
W. W. Mather observed that when pressed in chamois leather, or between the
fingers, some mercury is exuded. J. Schumann obtained an amalgam of sp. gr.
10386, containing 7-9 per cent, of platinum ; and J". P. Joule obtained products
with 12 to 43-2 parts of platinum to 100 parts of mercury. According to R. Bottger,
the dull black powder obtained by heating the amalgam over a spirit lamp still
retains xV^ 1 0 ^ i ta weight of mercury. Boiling the residue with cone, nitric acid
for 24 hours extracts only a trace of mercury, and the washed and dried residue
has a vigorous catalytic action on hydrogen gas and alcohol. If the amalgam be
heated to a higher temp., all the mercury is expelled, and grey, coherent platinum
remains which no longer inflames a jet of hydrogen. If, instead of heating the
platinum amalgam, it is digested with nitric acid, frequently renewed, the black
powder which remains is mixed with a few shining particles of platinum. It does
not ignite a mixture of hydrogen and air at ordinary temp., but does so if heated.
C. H. Latham studied the adsorption of water vapour by platinum amalgam.
According to R. Sabine, if a drop of dil. sulphuric, hydrochloric, oxalic, or acetic
acid be placed on the clean surface of a rich amalgam of a metal positive to mercury
—e.g. copper, zinc, antimony, tin, or lead—the drop does not remain still as it would
do on purified mercury, but sets itself into an irregular jerky motion ; but with
the amalgam of a metal negative to mercury—e.g. silver, gold, or platinum—the
drop of acid remains quite still. The movement is attributed to alternate oxidation