u*v».] PYRO-ELECTKIC PROPERTIES OF ALLOYS. 127 
3egun with absolutely pure materials. I fouud, too, that the purity 
jests which had originally been made were not rigorously sufficient; 
jhat portions of the single wire of platinum lying far apart differed 
nore seriously in their electrics than I had apprehended, and that the 
platinum itself when exposed before the oxyhydrogen blow-pipe during 
ong intervals of time (several hours) showed very measurable changes 
)f the constants which had originally characterized it, and must there- 
fore have changed somewhat in composition. An exhibit of the numeri- 
cal values of all discrepancies here involved will be given in the course 
>f the chapter. 
When so large a part* of the investigation had been completed, how- 
ever, it seemed expedient to push it to a close; for the classification 
liagram of the platinum alloys, which I was desirous of evolving, could 
aot lead to serious misapprehension if only the scale of representation 
ae chosen sufficiently small ; if the profile, in other words, were reduced 
x> a sufficiently small scale to make the errors negligible. Indeed, this 
ippeared desirable because no general study of the electrics of the pla- 
tinum alloys as complete as my own has as yet been made. Again, 
since in the scheme of fusing 2 per cent., 5 per cent., and 10 per cent, 
illoys, it was customary to use consecutive lengths of the platinum 
tfire, the results at least show the effect of alloying a specified metal to 
i given body of platinum. Finally, the plan of operation by which the 
tvork was done is worthy of description, and with the amount of expe- 
•ience gained in prosecuting this tedious research I will, at an early 
)pportunity, be able to repeat the work and bring the constants fully 
ip to the standard of accuracy desired ; in other words, to make the 
memical measurement compatible with the electrical measurements. 
Despite the discrepancies mentioned, this chapter is not barren in 
ipecial results; and perhaps my main motive in publishing the data is 
I ue to the fact that they lead to a relation between the electrical con- 
luctivity of platinum alloys and the temperature coefficient of that 
ponductivity, which is so nearly independent of the (alloyed) composi- 
ion of the metals that I feel urged to ascribe to it the importance of a 
aw. Very clearly does this appear when the present results for alloyed 
)latinuui are compared with a series of corresponding results long since 
bund by Dr. Strouhal and myself when working with steel. I filly 
)elieve that in endeavoring to explain the mechanism of electrical re- 
istance, the law in question will be more fruitful in suggestions than 
jny allied phenomenon which has yet been investigated. Inasmuch as 
used platinum appears to be the universal solvent for metals, the 
ncontestable importance of series of data such as I here endeavor to 
nvestigate is more obvious in proportion as the number of metallic 
ombinations obtainable is larger. 
To recapitulate, therefore, the law in question (I use the term " law" 
imply to facilitate expression) is independent of the ingredients of the 
Hoy except in so far as they modify its electrical conductivity. Alloy- 
(781) 
