406 Royal Society. 



heated for the first time to 100° and again cooled, an alteration in the 

 conducting power takes place ; with most metals it is necessary to 

 heat them for several days before their conducting power becomes 

 constant. In the third part we have deduced from the results ob- 

 tained, the law that all pure metals in a solid state vary in con- 

 ducting power to the same extent between 0° and 100° C. Incases 

 where very great accuracy is required, it is absolutely necessary to 

 experiment on the conductor itself ; for we have found almost the 

 same differences between formulae obtained for wires of the same 

 metal as between the mean of those deduced for the different metals. 

 This behaviour may be attributed to the fact that the molecular 

 arrangement is not the same even in wires of the same metal ; for we 

 find that copper wires, when kept at 100° for several days, behave very 

 differently from each other : thus, in the case of the three copper wires 

 experimented with, wire 1 increased in conducting power almost to the 

 same extent as if it had been annealed, wire 2 partially so, and wire 

 3 hardly at all. "With bismuth, wire 1 increased its conducting power 

 16 per cent.; wire 2, 19 per cent.; and wire 3, 12 per cent. Again, in 

 the case of cadmium, which becomes quite brittle and crystalline at 80° 

 (for cadmium may be powdered in a hot mortar), we found the 

 formula for each wire very different. On the other hand, the formulae 

 of the wires of those metals which, after being kept at 100° for some 

 time, show a very slight or no alteration in the conducting power 

 on again being cooled, agree very closely with each other. Compare 

 those of lead, tin, and mercury. 



Metalloids conduct electricity better when heated than when cold. 

 Ilittorf * proved this to be the case with selenium. Gas-coke and 

 graphite "f, and the gases J, follow the same law. Tellurium, when 

 first heated to 70° or 80° C., behaves as a metal, that is to say, it loses 

 in conducting power up to that temperature, when it then begins to 

 gain. The temperature of the turning-point becomes lower after each 

 day's heating, until, as with the first and third bars experimented with, 

 it is below the lowest temperature at which observations were made. 

 Taking the first observed conducting power of each bar =100, we 

 found that the conducting power of bar 1 had decreased after thirteen 

 days' heating to 4, where it then remained constant; that of bar 2, after 

 thirty-two days, became constant at 1 9 ; and that of bar 3, after thirty- 

 three days, at 6. With bar 2 the conducting power decreased up to 

 29° - 4, w r hen it began again to increase. The behaviour of tellurium is 

 therefore intermediate between that of the metals and that of the 

 metalloids. 



" Notes of Researches on the Poly- Ammonias. " — No. XIX. On 

 Aromatic Diamines. By A. "W. Hofmann, LL.D., F.R.S. 



• * Pogg. Ann. lxxxvi. 214. f Phil. Trans. 1858, p. 586. 



% Ann. de China, et de Phys. (3) xxxix. 355. 



