barus.] PYRO-ELECTRIC PROPERTIES OF ALLOYS. 163 
paoied by a modification of molecular structure. Tbe passage from the 
molecular type, which characterizes the first metal in the pure state, to 
the type which characterizes the second pure metal in the alloy is un- 
doubtedly so complex that it is only on approaching very near the pure 
metals that the nature of the elementary principles of such a passage 
can be discerned. This is the interpretation which T venture to give 
to the linear loci investigated. Perhaps the following comment will 
make my meaning clearer : 
The temperature-coefficients for pure metals are nearly constant and 
independent of the resistances of the metals themselves, whereas their 
specific resistances vary enormously. Hence the locus (Fig. 27), if ex- 
tended for higher percents, must show very decided curvature. More- 
over, there will be a special locus for each metal alloyed to platinum, 
which will terminate in the particular co-ordinates /(0),/ / (0): /(0) of 
the metal iu question. It is in the neighborhood of the two pairs of 
f{®)i f'W : /(0)> wn ich (one pair at each end) terminate the locus ex- 
pressing the general relation between these two quantities, that the 
curious linear relation iu question seems to hold. 
In view of the fact that the relation between /(0) and /'(0) : /(0) 
must ultimately be curvilinear, the inferences to be derived from equa- 
tion 6 by making either /(0)^=0 or /'(()) : /(0)=0 are necessarily in- 
volved. To interpret it, similar relations would first have to be devel- 
oped for low percentage alloys of many other metals. Nevertheless, 
these considerations are suggestive. They point to a limit, below which 
neither the electrical conductivity of metals nor the temperature-co- 
efficient can be reduced. It appears therefore that a lower limit, both 
Of conductivity and of temperature-coefficient, is among the conditions 
Of metallic conduction, not to say of metallic state. 
To make what I have here in mind clearer I will premise the follow- 
ing: In the case of conduction of electricity in metals (solid or liquid) 
the effect of temperature is a decided decrease of conductivity, continu- 
ing so long as temperature increases. In the case of conduction in 
uon-metals or in electrolytes (solid or liquid), on the other hand, the 
affect of temperature is a decided increase of resistance, which, suppos- 
ng the liquid state to be retained, continues as temperature increases. 
Sence conduction in metals is distinguished from conduction in elec- 
trolytes in this respect, that if the temperature-coefficient in one case 
metals) be regarded positive its value in the other case (electrolytes) 
;vill necessarily be negative. Applying these general principles to the 
ibove inferences for alloys, it appears that the occurrence of a lower 
imit of electrical conductivity and of temperature-coefficient in the 
ase of alloys may be regarded as significant or as being a unique ex- 
pression of one of the conditions of metallic conduction. 
I am thus led to inquire into the nature of that class of substances 
^hose temperature-coefficient is zero ; a class of substances, in other 
yords, in which the metallic and the electrolytic modes of electric con- 
(817) 
