COJ^DUCTING POWEE OP ALLOTS. 
175 
view, with the conducting power for heat, in order to see if the classification of the 
metals and alloys given in this paper will hold good for any of, the other physical pro- 
perties, as well as in the hope of finding out the cause of the behaviour of the metals of 
Class B. when alloyed with traces of any other. On looking at the specific gravity of 
alloys*, we find that they cannot be classified as above, but in all probability the above 
classification will hold good for their tenacity, hardness, conducting power for heat, &c. 
APPENDIX. 
On the Electric Conducting Power of Pure Gold, 
The values given for the conducting power of pure gold, in my paper “ On the Elec- 
tric Conducting Power of the Metals f,” is not quite correct, as the gold from some 
cause cannot have been chemically pure ; although prepared with the greatest care by 
Dr. Metboom, yet the whe-drawer in all probability fused it in a crucible which had 
been pre\iously used ; and as only 3 to 4 grms. were purified, a very small amount of 
impurity would account for the difierence which I have lately found. At the time the 
values appeared veiy low, compared with those of other experimenters, but it was then 
thought that the higher ones were due to traces of silver. Experiments, however, have 
proved, on the contrary, that most of the gold-silver, gold-copper, &c. alloys conduct 
electricity worse than pui’e gold ; and that, in fact, only those which contain less than 
2 per cent, gold in gold-silver alloys, and about 3 per cent, gold in gold-copper alloys, 
conduct better than pure gold. 
Thus chemically-pure gold, prepared by dissolving gold from the refiners in nitro- 
hydrochloric acid, precipitating with algaroth powder, washing alternately with nitric 
and hydrochloric acids, redissolving in nitrohydrochloric acid, precipitating by sul- 
phurous acid, w’ashing alternately with nitric and hydrochloric acids, and fusing in a 
muffle with nitrate of potash, gave, compared with a hard drawn silver wire =100 at 0°C., 
I. II. III. Mean. 
73-57 at 19°-0 72-10 at 19°-1 72-37 at 19°-8 72-68 at 19°-3. 
Another specimen, prepared in the same manner, gave 
I. II. III. 
72-80 at 23°-0 73-42 at 23°-8 73-02 at 23”-l 
Mean. 
73-08 at 23°-3. 
A third specimen, prepared by dissolving gold containing silver in nitrohydrochloric 
acid, evaporating to dryness with excess of hydrochloric acid, dissolving in about 500 
times its weight of water and precipitating with protosulphate of iron, washing out all 
* See specific gravities of tin-bismuth and lead-bismuth aUoys in this volume, pp. 162, 165, 166. 
t Philosophical Transactions, 1858. 
+ It is of the greatest importance, in purifying gold containing silver by this method, that the solution 
should he made very dilute, so that the chloride of silver dissolved in the chloride of gold may be precipi- 
tated before the addition of the protosulphate of iron ; otherwise the chloride of silver would fall with the 
