334 Profs. Dewar and Fleming on Electrical Resistance 



On charting the above figures for the alloys, it is found that 

 the resistance-lines are very nearly straight lines with but 

 little slope, not one-tenth that of the pure metals, when the 

 constituent metals of the alloy are chemically very different. 

 This is the case with the platinum-silver, platinoid, and 

 German-silver alloys. When, however, the constituents of 

 the alloy are chemically similar, as in the case of the 

 platinum-iridium and platinum-rhodium alloys, the resistance- 

 lines plotted in terms of the absolute temperature slope down 

 at a much steeper angle, but never, as in the case of the pure 

 metals, in such manner as to indicate that if prolonged they 

 would pass through the absolute zero. In a similar manner 

 the impure metals also behave. We have laid down on such a 

 resistance-temperature diagram the lines representing the 

 change of specific resistance with temperature for palladium 

 not known to be pure, for nickel not pure, for commercial 

 iron wire, for ordinary bismuth, for gold not pure, and other 

 commercial metals, and found that the resistance-lines of 

 these metals do not slope down at such an angle as to indi- 

 cate that if prolonged they would pass through or near the 

 origin or absolute zero. The lines for these impure metals 

 are in position more or less like the lines for alloys formed 

 of similar metals. 



§ 6. Another fact of considerable interest has been ascer- 

 tained. We know that for temperatures above zero Centi- 

 grade carbon behaves like an electrolyte as regards change of 

 resistance with temperature, that is, its specific resistance 

 decreases as temperature increases. Hence it was a matter 

 of importance to examine the behaviour of carbon as regards 

 electric resistance when cooled to — 182° in liquid oxygen. 

 For this purpose we employed the carbon filaments of in- 

 candescence lamps, taking the treated filaments of Edison- 

 Swan lamps and the dense adamantine carbon employed in 

 the Woodhouse and Rawson incandescence lamp. In both 

 cases we found that when cooled to this low temperature the 

 specific resistance of the carbon continuously increased instead 

 of decreasing, as do the metals. The following Table III. 

 gives the specific resistance (p) in electromagnetic units of 

 these carbons at various temperatures. 



§ 7. We have not yet completed the examination at similar 

 low temperatures which we propose to make of the behaviour in 

 regard to electrical resistance of such non-metals as selenium 

 and sulphur, and such metals as arsenic and antimony, with 

 marked chemical affinities with non-metals. Also the be- 

 haviour of such insulators as mica, glass, guttapercha, india- 

 rubber remains to be examined. It is known that the 

 electrical resistance of these bodies decreases with rise of 



