with
silver (at least five times the quantity of platinum present), copper
(a quantity equal to that of the platinum), and lead, cupelled at as
high a temperature as possible and the residue fused for from 3 to 5
minutes. The resulting button is rolled to a thickness of 0.2
millimeter and heated for one-fourth of an hour with diluted sulphuric
acid (100 volumes of concentrated acid to 22 volumes of water) at a
temperature not exceeding 240° C. The treatment with acid is repeated
twice, and the residual platinum is washed, dried, and weighed.
This method is of course open to the same objection as that noted in regard to Dewey's procedure.
L.
J. Curtman and P. Rothberg have recently proposed' a new method for the
detection of the platinum metals in which, however, the various
elements of this group can not be distinguished. It is based on the
glow reaction exhibited by finely divided platinum, palladium, rhodium,
or iridium when passing over it a mixture of air and illuminating gas.
The substance to be tested is brought into solution by any of the
common methods and about 0.2 centimeter of the solution is absorbed
into a piece of thin asbestos paper by alternately dipping the paper
into the solution and heating until the required volume has been
absorbed. The paper is now heated to redness in the flame and then
removed, and while the paper is still warm it is brought into a stream
of a mixture of illuminating gas and air from a Bunsen burner. If
platinum or allied metals is present the paper will begin to glow. The
glow must last for some time, and the effect can be repeated. The
asbestos paper must be very thin. This test is sensitive to extremely
small quantities of the metal, the limits being: Platinum, 0.002
milligram; palladium, 0.0005 milligram; rhodium, 0.0009 milligram; and
iridium, 0.005 milligram. The presence of other substances does not
interfere with the test.
INFLUENCE OF IMPURITIES IN PLATINUM WARE.
It
has long been known to chemists that certain kinds of platinum ware are
more rapidly attacked by coal gas than others. A recent report of the
Physikalisch-technische Reichsanstalt2 deals with this
subject. It appears that platinum containing 3.5 per cent of iridium
separates carbon from coal gas very much more rapidly than pure
platinum. Another test on two pieces of platinum which had been used
under similar conditions, one of which had deteriorated rapidly while
the other had not, gave as the only ascertainable difference 0.2 per
cent of rhodium in the bad sample and 0.1 per cent in the good.
The
general conclusion is that platinum containing iridium is more strongly
attacked in a current of illuminating gas at 650° C. than pure
platinum. A number of papers have lately appeared dealing with the
quality and deterioration of platinum utensils. A preliminary report of
a committee on quality of platinum laboratory utensils3 was
recently published, and its authors, W. F. Hillebrand, P. H. Walker,
and E. T. Allen, present some interesting and valuable conclusions.
They state that the quality of much, if not all, of the platinum ware
made in this country in recent years is markedly inferior to that which
was procurable many years ago. One cause for this is said to be the use
of scrap platinum for laboratory utensils. The objections made to the
inferior ware are (1) undue loss of weight on ignition,
i Tour. Am. Chem. Soc., vol. 33, May, 1911, pp. 718-723.
2 Kept. Phvsikalisch-techn. Reichsanstalt on platinum: Zeitschr. Instramentenkunde 30, 1910, p. 190.
a Jour. Indiist. and Eng. Chem., vol. 8, No. 9, September, 1911.
