146 MEASUREMENT OF HIGH TEMPERAUURES. Ibull.54. 
alloys, large discrepancies sometimes occur, showing that in these in- 
stances the base metal can not have been perfectly dissolved nor the 
alloy satisfactorily homogeneous. Inasmuch, however, as the method 
of comparing the specific resistance of the ingot as a whole, as it were, 
with a small part of the wire drawn from it is a very rigorous test for the 
homogeneity of the alloy, it appears from the coincidence of the results 
for s t I and s t II, that melted platinum may indeed be regarded as a 
solvent for metals generally. The importance of this quality has already 
been signalized above. 
Resistance and thermo-electrics.— It has been stated that the thermo- 
electric results are the ones most influenced by impurities in the plati- 
num, for the alloys of this metal, though exhibiting enormous differences 
of resistance, are, with few exceptions, relatively without marked thermo- 
electric variability. This is an observation of importance, particularly 
if considered with reference to the position of the individual alloys in 
the series. It shows that there is probably no intrinsic relation what- 
ever between specific resistance and thermo-electric power when the 
variations of both the quantities are produced by alloying. Curiously 
enough the extremes of the thermo-electric variations are the cobalt and 
the nickel alloys, the former being powerfully positive, the latter even 
more powerfully negative. The iridium alloy has the well-known ex- 
treme electro-negative position, as would also have the molybdenum 
alloys. On the other hand, the positions of iron, of chromium, of man- 
ganese are not nearly as extreme as would have been anticipated from 
their resistance values, whereas the powerfully resisting combinations 
of platinum-copper, platinum-zinc, platinum-tin show only insignificant 
values of thermo-electric power. In short, there appears to be no law 
for the co-ordination of the galvanic and therrno electric qualities dis- 
cernible, and large values in the one case by no means imply large 
values in the other. 
Electrical tests for purity. — Having thus briefly discussed the thermo- 
electric and resistance data in the above tables, it will be next in place 
to describe the experiments made to ascertain the condition of purity 
of the platinum used. These experiments have special importance, be- ; 
cause they exhibit the electrical behavior of commercial platinum fre- 
quently treated before the oxyhydrogen blow-pipe, and therefore show 
what degree of purity of platinum is necessary in order that the metal 
may be safely used practically in thermo-electric temperature measure, 
ment. 
The original experiments made with a length marked A, and cut 
from the coil above described, behaved in such a way as to give rise toj 
no serious apprehensions. This piece was first annealed, and then 
therrno- electrically combined with No. 0, as were the wires in Table 32. 
• (800) 
