128 MEASUREMENT OF HIGH TEMPERATURES. [bull.5 
ing is here merely a method of modifying resistance, and the resull 
are studied with regard to the resistance produced, not with regard 1 
the way in which resistance is modified. In all of this work the chi< 
object is to get nearer the true nature of electrical resistance, as 
means possibly subsidiary to arriving at some results relative to th 
nature of electricity itself. 
FUSION AND MECHANICAL TREATMENT OF THE ALLOYS. 
Fusion, rolling. — It has just been stated that it was my purpos 
to obtain groups of 2 per cent., 5 per cent., and 10 per cent, platinur 
alloys of as many metals as possible. The quantities were therefor 
weighed out in proper proportion and fused on a lime hearth, befor 
the oxyhydrogen blow-pipe. The blow-pipe is identical with the on 
described in the next chapter. The hearths consisted of cubes or red! 
angular solids, cut with a hack saw from a large lump of lime as fre 
from fissures as possible. Into each of the sides semicircular cavitie 
were dug, with a semicircular -faced drill, on the lathe. Nickel, gold 
copper, palladium, and tin were quietly absorbed by the melted plat; 
num globule. Silver boiled perceptibly. Iron, and more particular! 
aluminium and manganese, were absorbed explosively. Chromium 
cobalt, and even iridium were apt to splutter. Zinc, molybdenum, an 
timony, bismuth, lead, must be frequently added, but the quantity ab 
sorbed was usually sufficiently large to change the qualities of platinui!! 
perceptibly. With regard to rolling, it may be stated that the 10 pe 
cent, gold and the 10 per cent, tin alloys are too brittle, and must there 
fore be diluted with further amounts of platinum. In the same way 
per cent, chromium, 5 per cent, aluminium, 10 per cent, copper, and H 
per cent, nickel alloys, and others, usually break on rolling. Cobal i 
alloy, moreover, absorbs gas and inflates itself on cooling. Iron alloy 
10 per cent., could be rolled by superficially fusing the rifts. This ex 
pedient, though not rigorously in favor of homogeneity of compositioo 
had to be frequently resorted to; for instance, in case of antimony, bis 
muth, zinc, silver, and lead alloys which are more or less porous afte] 
fusion. Curious properties seem to be possessed by the tin alloys, in 
asmuch as the 10 per cent, alloy is brittle and hard enough to scratcl 
iron. Experiments were made in rolling hot ingots, but with doubtfu 
success, the quantities being too small to retain their heat for any length 
of time. I add, finally, that the work threw some light on the con 
ditions of diffusion of any liquid metal in any other liquid metal, a 
phenomenon as yet imperfectly known. 
Preliminary data, density. — In all about fifty-two alloys were fused tc 
buttons. These were then rolled to little bars of platinum about 10 Ctt 
or more in length, and about 0.013 D cm in section. Alloys of this length 
and section are suitable for preliminary measurements of resistance 
and density. The; data for density are given in Table 29. They were 
obtained by suspending the platinum rods from a fiber of silk in a long 
(782) 
