518 



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. 

 Hittorf * proved this to he the case with selenium. Gas-coke and 

 graphite f, and the gases , 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, when it began again to increase. The behaviour of tellurium is 

 therefore intermediate between that of the metals and that of the 

 metalloids. 



III. "Notes of Researches on the Poly- Ammonias/' No. XIX. 

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

 Received December 16, 1861. 



Whilst engaged in the examination of the polyatomic ammonias of 

 the ethylene-series, I have repeatedly endeavoured to produce the 

 diatomic bases corresponding to the aromatic monamines. The 

 composition and general characters of these compounds were suffi- 

 ciently indicated by the examination of ethylene-diamine. The 

 simple relation which the latter body bears to ethylamine, 



Ethylamine H V N, Ethylene-diamine H V N,, 



H 



could leave no doubt regarding the existence of a series of diatomic 

 aromatic ammonias similarly related to aniline and its homologues. 



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



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



