ON THE CHEMICAL NATURE OF ALLOYS. 39 
different proportions* and allowed to crystallize, the alloys containing from 
20-33 per cent. zine crystallize in silver-white rhombic crystals, P: P (P: P 
at the terminal edges 118° 24’ and 95° 24’, at the lateral edges 115° 30’), and 
those containing from 43-70 per cent. zinc in rhombic prisms of 117° 63’ 
truncated at the edges. Further, it has been shown that the alloys of tin 
and gold containing from 25-43:5 per cent. gold crystallize all in the same 
formt. ‘This is therefore an important point to bear in mind, for it follows 
that alloys of a definite crystalline form are not necessarily chemical com- 
binations. 
3. Points of Fusion.—It is a matter of common observation that the fusing- 
point of a mixture is lower than the mean fusing-point of the constituents. 
The fluxes so well known in metallurgy exemplify this, as also do the alloys, 
as well as mixtures of the solid fatty acids. There is I believe no case known 
where the fusing-point of a mixture is higher than the mean fusing-point, 
of the components. 
This fact admits of explanation as follows :— 
It is generally admitted that matter in a solid state exhibits excess of attrac- - 
tion over repulsion, whilst in the liquid state these forces are balanced, and in 
the gaseous state repulsion predominates over attraction. Let us assume that 
similar particles of matter attract each other more powerfully than dissimilar 
ones attract each other. It will then follow that the attraction subsisting 
between the particles of a mixture will be sooner overcome by repulsion than 
will the attraction in the case of a homogeneous body ; hence mixtures should 
fuse more readily than their constituents. : 
To the second class of properties belong 
Conducting-Powers for Heat and Electricity According to some experi- 
menters the values obtained for the conducting-power of the metalst and 
alloys§ for heat and electricity are the same; so that, if either of these pro- 
perties be determined for a series of alloys, we shall then be able to deduce 
their chemical nature: but before going into this subject more widely let me 
say a word respecting the other physical properties. To which of the two 
elasses many belong it is at present impossible to say ; for the results obtained 
by different observers vary so much, and in most cases only a very few 
alloys have been experimented with. There is, however, no doubt that the 
determination of some of the other physical properties would materially aid 
us in ascertaining the chemical nature of the alloys; but in order to obtain 
such results as will aid us in the inquiry, it is absolutely necessary to employ 
only purified metals. I do notsay chemically pure ; for no chemist would give 
much credit to anyone stating that he had prepared 5 to 10 kilogrammes of 
any metals in a state of chemical purity, such being the quantities required 
to carry out one such research. The only manner to proceed in such cases is 
to satisfy oneself, by repeatedly purifying and by using metals of different 
preparations by different methods, that the amount of impurity remaining 
with the metal has no influence on the results obtained. For of what use is 
a research into the physical properties of the metals and their alloys made 
with impure metals, when we know that traces of impurity materially affect 
and alter them ? 
I will now proceed to show how we may deduce the chemical nature 
* J. P. Cooke, Journ. Amer. Acad., New Series, vol. v. p. 337. 
+ Matthiessen and v. Bose, Proc. Royal Soc. (1861) vol. xi. p. 433. 
+ Wiedemann and Franz, Pogg. Ann. vol. Ixxxix. p. 497. 
§ Wiedemann, Pogg. Ann. vol. cviii. p. 393. 
