ON THE CHEMICAL NATURE OF ALLOYS. 47 
slowly, different parts of the alloy will be found to contain different percent- 
ages of metal. 
Having shown, by examples taken from different groups of alloys, how 
their chemical nature may be indicated by the determination of their con- 
ducting-power for electricity, I will proceed to classify the solid alloys com- 
posed of two metals, according to their chemical nature :— 
1. As solidified solutions of one metal in another, we have the lead-tin, 
cadmium-tan, zinc-tin, lead-cadmium, and zine-cadmium alloys. 
2. As solidified solutions of one metal in the allotropic modification of the 
other, the lead-bismuth, tin-bismuth, tin-copper, zinc-copper, lead-silver, 
and tin-silver alloys. 
3. As solidified solutions of the allotropic modification of metals in one 
another, the bismuth-gold, bismuth-silver, palladium-silver, platinum-silver, 
gold-copper, and gold-silver alloys. 
4, As chemical combinations, the alloys the composition of which is re- 
presented by Sn, Au, Sn, Au, and Au, Sn. 
5. As solidified solutions of chemical combinations in one another, the alloys 
whose composition lies between Sn, Au and Sn, Au, and Sn, Au and Au, Sn. 
6. As mechanical mixtures of solidified solutions of one metal in another, 
the alloys of lead and zinc when the mixture contains more than 1-2 per cent. 
lead or 1-6 per cent. zinc. 
7. As mechanical mixtures of solidified solutions of one metal in the allotropic 
modification of the other, the alloys of zinc and bismuth when the mixture 
contains more than 14 per cent. zinc or 2-4 per cent. bismuth. 
8, As mechanical mixtures of solidified solutions of the allotropic modifi- 
cations of the two metals in one another, most of the silver-copper alloys. 
With regard to the hypothesis which I have brought forward in this Report, 
I would point out that it serves to explain the phenomena which take place 
when some metals are alloyed with others. The assumption of the existence 
of the allotropic modifications of the metals explains the turning-points of the 
curves which represent alloys containing very small percentages of the one 
metal ; for at these points it is assumed that the conversion into the allotropic 
condition is complete, It must be borne in mind that most of the other phy- 
sical properties of the metals belonging to Class B are also altered in a marked 
degree by the addition of a small percentage of another metal: take, for 
instance, the case of gold or silver, and alloy them with traces of tin or lead, 
and how altered are the tenacity and ductility of the alloy so formed ! 
Until, however, the allotropic modifications have been isolated, the assump- 
tion made in this Report must remain an hypothesis. A fact may be mentioned 
in its support ; namely, sulphur:when heated to a temperature of 60°, and 
then cooled rapidly, is converted into an allotropie modification. Dietzenbach 
has observed that this conversion is brought about at 120° if ,1, of iodine be 
added to the sulphur, showing that the presence of a small quantity of iodine 
has a marked effect on the conversion of sulphur into an allotropic condition. 
It may be asked, How can we deduce the chemical nature of a series of 
alloys from the determination of a physical property such as their conducting- 
power for electricity? We reply, from this property taken alone it is impos- 
sible to draw any conclusion of the kind, but that since, in the case of those 
-alloys whose constitution is known by direct chemical and other evidence 
(silver-copper (Levol), zinc-copper (Storer), gold-silver), their conducting- 
_power is found to be such as their chemical constitution would lead us to ex- 
pect, this property may legitimately be taken in evidence as to the nature of 
those alloys which have not been examined chemically, and that in this respect 
