CONDUCTING POWEE OP ALLOTS. 
173 
For the above reasons I think there can be no doubt that the irregularity of the gold-tin 
curve is due to chemical combination, and that the same may be said of the gold-lead 
curve. 
That some alloys are mechanical mixtures, we know from facts determined by other 
experimenters; thus, when we fuse 17'73 parts of bismuth and 16T2 parts of zinc toge- 
ther, we find two layers, the upper one consisting of 13'40 parts of zinc, and the lower 
one 19 ‘40 parts of bismuth alloyed with traces of zinc*; now had we stirred the two 
metals well together, and cooled rapidly the alloy so obtained, it might be considered as 
a mechanical mixtiu’e. 
Again, according to LEVOLf, if we fuse silver and copper together, and allow the 
alloy to remain quietly in the fused state, we find, on analysing the mass, that different 
parts contain different per-centages of metal : he found this to be the case with all 
alloys, excepting that containing 28T1 per cent, of copper, which corresponds to the 
formula Agj CU 4 . 
Levol regards all alloys of silver and copper as mixtures of Agj CU 4 , and either 
silver or copper; if this were the case, we should have expected to find from that 
point to pure silver or copper, straight lines ; but on examining that curve, starting from 
the copper side of it, we fiii’st see that a rapid decrement takes place, caused by the 
copper being alloyed with a small quantity of silver. From that alloy containing 90 vols. 
per cent, to that of 35 vols. per cent, of copper, we have a straight line, and we may 
regard the intermediate alloys as mixtures or solutions of these two alloys ; from the 
alloy containing 35 vols. per cent, to that with 28 vols. per cent, of copper, we may have 
a mixture or solution of those alloys : now this last point is the minimum point of the 
curve, and coiTesponds almost to Levol’s Agg Cu^, being an alloy containing 25 per cent, 
by weight of copper. This, as well as the other lowest points of the curves, must not 
be considered as actually the lowest, but only as the lowest point found ; for in this case 
we should expect that the alloy containing 28 per cent, of copper would be lower; and 
from this point to pure silver the alloys may be mixtures, or perhaps solutions of that 
alloy and silver containing a small quantity of copper. Now it would appear as if at about 
the point which represents the alloy containing 35 vols. per cent, of copper, there was 
also one of constant composition, otherwise we should have expected a straight line from 
the alloy containing 28 vols. per cent, to that containing 90 vols. per cent, of copper. 
Of course, from this one cuiwe, w*e can hardly deduce any conclusions, as we have in 
all probability to deal with mixtures of chemical compounds, with solutions of the one 
metal in the other, &c. It only shows that, by the determination of the conducting 
powers of the alloys, we are able to tell where these are constant or chemical combina- 
tions ; and when the curves are irregular, we may safely conclude that we have to do 
with chemical combinations or mechanical mixtures. 
That the first group of alloys, their curves being nearly straight lines, are not mix- 
* Eoviixet, Ann. de Cliim. et de Pliys., vol. liv. p. 247. 
t Joum. de Pharm., vol. xvii. p. 111. 
