A Comprehensive Treatise on Inorganic and Theoretical Chemistry

20O INORGANIC AND THEORETICAL CHEMISTRY
a comparison of the ratio of the thermal, Jc, and the electrical, K,
at 25°, by F. A. Schulze.
conductivities
Platinum
JtXlO* .
k/JCxlO 7
.
O
57-35
69
10
12-72
77
25
4-23
9O
3O
3-22
95
33 per cent
305
106
W. Geibel's results for the thermoelectric force of platinum, E millivolts, against
platinum-silver alloys are indicated in
Fig. 40 ; and those of C. H. Johansson
and J. O. Linde for the platinum-silver
20 40 60 80 100
Atomic per cent, of platinum
FiO. 39. Electrical Resistance of the
Platinum-Silver Alloys.
alloys against silver, at 18°, in Fig.
41. Observations were also made by
A. W. Smith, W. H. Keesom and
J. N. van Ende, C. G. Knott and
J. G. McGregor, W. Broniewsky,
V. Strouhal and O. Bams, and H. Tomlinson
; and the thermoelectric force
against copper was measured by
J. Klemencic. F. Braun observed
that when spluttered by a current
from a Leyden jar, the alloy separates
into its constituents. D. A. G. Bruggeman
studied the dielectric constants.
F. E. Carter observed that even
but a lew per cent, of platinum in
silver reduces the rate of tarnishing
of the silver. According to J. P. J.
d'Arcet, sulphuric acid dissolves only
silver from platinum silver alloys.
J. F. Thompson and E. H. Miller
found that all the silver is dissolved
only from alloys containing 90 per
cent, or more silver ; alloys with less
silver do not give it all up to the acid. Thus,
Silver in alloy-
Silver in residue
89-61
Trace
79-41
O-59
68-54
0-98
62-11
2-24
42 95 per cent.
2-70
A small trace of platinum is inclined to dissolve with the silver, but by diluting
the acid, this may be prevented. The subject was also studied by H. Carmichael ;
100" 300° 500° 700" 900°
!PlO. 40. Thermoelectric Properties of the
Platinum-Silver Alloys against Platinum.
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V S
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1
20 40 60 80 1OO
Atomic per cent, of platinum
Fio. 41.—Thermoelectric Properties of the
Platinum-Silver Alloys against Silver.
and A. Steinmann recommended the use of a soln. of 100 vols, of acid and 22 vols,
of water for dissolving out the silver, the operation being twice repeated at 240°.