A Comprehensive Treatise on Inorganic and Theoretical Chemistry

PLATINUM 207
T. Cooper prepared a platinum-copper-zinc alloy by melting a mixture of the
first two metals covered with borax and carbon in a crucible at a white-heat, and
stirring in the zinc when the crucible had been taken from the furnace. The goldcoloured
alloy does not rust, and it is attacked only by boiling nitric acid.
J. J. Burle, and C. Krug also prepared these alloys. J. J. Burle also prepared
platmum-copper-srilver-zinc alloy. L. Nowack studied the age hardening of the
platinum-gold-zinc alloys. F. Stromeyer prepared a platinum-cadmium alloy
by heating platinum with an excess of cadmium until the excess is volatilized.
A. Pospieloff, and W. R. E. Hodgkinson and co-workers also obtained an alloy
by the action of the vapour of cadmium on platinum ; and F. Mylius and O. Fromm,
by the precipitation of platinum by cadmium from soln. of platinum salts.
K. W. Ray studied the equilibrium diagram.
F. Stromeyer, and W. R. E. Hodgkinson and co-workers' products corresponded
with platinum dicadmide, PtCd2. The silver-white, fine-grained product
is very brittle. Its sp. gr. is 13*53 at 15°—calculated 12-59. Scarcely any cadmium
volatilizes from the alloy at a red-heat. When digested with nitric acid, some
platinum passes into soln. along with the cadmium. All the alloys with over
6 per cent, of platinum were found by K. W. Ray to be very brittle, and harder
than either metal component. The cadmium is dissolved out by hydrochloric or
sulphuric acid, leaving spongy platinum behind.
B. Wood noted the brittleness of these alloys. C. T. Heycock and F. H. Neville
observed that the f.p. of cadmium is lowered about 4*5° by the addition of 1 at.
per cent, of platinum. K. W. Ray found that platinum dissolves in molten cadmium,
forming white alloys having a low m.p. The f.p. curve shows that platinum
dicadmide, PtCd2, and platinum hemienneacadmide, Pt2Cd9, are formed. The
hemienneacadmide decomposes at 615° into cadmium and the dicadmide, which
melts at 725°. The eutectic with 2 per cent, of cadmium and the hemienneacarbide
melts at 315°. Cadmium volatilizes rapidly during the preparation of alloys with
over 50 per cent, of platinum, and the pasty mass can be melted only under press.
C. Barus made some measurements of the electrical resistance, and of its temp,
coeff. Gr. Tammann and W. Wiederholt studied the polarization of the alloy.
F. Mylius and O. Fromm found that hydrogen is given off turbulently when the
alloy is treated with hydrochloric acid.
J. F. Danielle R. Bottger, E. Melly, I. N. Plaksin and S. M. Schtamova, and
C. Engler and Li. Wohler prepared platinum-mercury alloys, or platinum amalgams
by triturating spongy platinum with mercury. R. Bottger used a warm mortar,
and J. F. Daniell found that the amalgamation is facilitated if 'water acidified with
acetic acid is also present. C. Engler and Li. Wohler observed that owing to
occluded oxygen, and oxidation films, platinum black amalgamates with difficulty ;
and M. Tarugi, that the grey mercury which separates when magnesium is added
to a soln. of mercury salt, does not amalgamate platinum black by trituration.
A. Tribe observed that platinum black which has been treated with hydrogen
readily amalgamates with mercury in a few hours. T. Ihmori showed that platinum
black absorbs mercury vapour; and C. Hockin and H. A. Taylor, that platinum
rapidly amalgamates with mercury boiling in an evacuated vessel.
J. F. Daniell observed that compact platinum does not take up mercury at
ordinary temp, even when kept in contact with it for 6 years, but if the mercury
be heated—to 200°, according to F. E. Carter—the metal acquires a film of mercury
which can easily be wiped off ; and J. M. Crafts added that a small proportion of
mercury is taken up by the metal. E. N. Horsford also noted that compact platinum
does not take up mercury at ordinary temp. M. Krouchkoll emphasized that for
amalgamation, the surface of the compact metal should be thoroughly cleaned,
and he recommended dipping the platinum in boiling nitric acid, and heating it
to redness many times. W. Skey showed that the contact of platinum with aq.
ammonia or alkali-lye prevents amalgamation by oxidizing the surface of the
metal, but the metal amalgamates if in contact with mineral acids. G. McP. Smith