42 ' REPORT—1868. 
That these alloys in the solid state are not chemical combinations is 
indicated, First, by their having the theoretical conducting-power, as well 
as the theoretical percentage decrement * in their conducting-power between 
0° and 100°C. ; for the following law has been found to hold good for all 
alloys of the first and third groups, as well as for a part of those belonging 
to the second: The observed percentage decrement im the conducting-power of 
an alloy between 0° and 100°C, ts to that calculated between 0° and 100° C, as 
the observed conducting-power at 100°C. is to that calculated at 100°C, 
Secondly. It may be urged that the solidifying point not always being the 
same as the point of fusion (for instance, in the lead-tin alloys), and the 
existence of the so-called stationary points, is a sign of chemical combination. 
They certainly do point to the probable existence of chemical combinations in 
the liquid alloy, but not in the solid. That chemical combinations may exist 
at high temperatures in a fused mass, which suffer decomposition on cooling 
or solidifying, becomes very probable from the following experiment :—When 
iron and excess of iodine are heated together in a stout glass tube, the iodine 
combines with the iron to form a compound, which decomposes with eyolu- 
tion of iodine on being cooled, the protiodide of iron remaining behindt. 
Wanklyn and Carius, who made the above observation, suppose that at the high 
temperature the periodide of iron is formed, and that, on cooling, this salt 
splits up into the protiodide of iron and free iodine. May we not assume that 
what has been shown to occur with iodine may also occur with other elements 
—oxygen, for instance, it forming with some bodies at high temperatures 
oxides which suffer decomposition with evolution of oxygen at lower. ones, 
This would then give us the explanation of the spitting of silver. Supposing, 
therefore, that chemical combinations can exist at high temperatures which 
suffer decomposition on cooling, we can then understand why some alloys 
fuse at one temperature and solidify at a lower one: for example, the tin-lead 
alloys, according to Pillichodyt, 
Sn,Pb. Sn;Pb. Sn, Pb. SnPb. SnPb,. SnPb,. Sn Pb, 
Fuse.... 187 181° 197 235 270 2838 998 
Soldify: 27182 181"! 181 aga eget int da nL 
who makes the following remarks on them :—‘‘ When the points of solidifica- 
tion are observed by immersing the thermometer in the melted alloy, it 
usually exhibits, during the passage of the mass from the liquid to the solid 
state, two stationary points. This effect is due to the separation of one or other 
of the component metals, while an alloy of constant composition still remains 
liquid. This alloy has the composition of Sn, Pb. An alloy richer in lead 
would first deposit lead, and an alloy containing a larger proportion of tin 
would first deposit tin,—the alloy Sn, Pb remaining liquid for a longer or 
shorter time, and ultimately solidifying at 181°. This temperature therefore 
corresponds to the lowest melting-point that can be exhibited by an alloy of 
tin and lead, a larger proportion of either metal causing the melting-point to 
rise.” 
These low fusing-points are no proof of the existence of chemical combina- 
tions in the solid alloy, but admit of explanation by assuming that chemical 
attraction between the two metals comes into play as soon as the temperature 
rises, and the moment the smallest portions melt, then the actual chemical 
compound is formed which fuses at the low temperature, and then acts as a 
* Matthiessen and Vogt, Proceedings of the Royal Society, vol. xii. p. 652. 
t Liebig’s Ann. vol. cxx. p. 69. ¢ Journ. Chem. Soe. vol. xy. p. 30. 
