1889.] A. Pcdlev— Volatility of some of the Compounds of Mercury. 189 



IX. — On the Volatility of some of the compounds of Mercury and of the 

 Metal itself. — By Alex. Pedlek. 



I propose only in the present paper to add a few facts to those 

 already known on the subject of the volatility of mercury and of somo 

 of its compounds. Popularly, the liquid metal mercury, or quiclcsilver, 

 may be considered to be a typical case of a liquid which is non-volatile. 

 This, however, is not the case, and the volatility of mercury has been 

 the subject of many researches. Faraday* was one of the first to notice 

 that mercnry is sensibly volatile even at the ordinary temperature of 

 the air, and he states that this is the case between 15'5° and 27°, but not 

 at 6"7°, both in spaces filled with air and in vacuo. This volatility of 

 mercury was proved by suspending gold leaf for 2 months in a vessel 

 over mercury, when the leaf became amalgamated. This volatility is 

 also proved by the old process of daguerreotyping, and by the fact that, 

 if a current of electricity is passed through a Torricellian vacuum or 

 through Geissler's tubes which are being exhausted with a mercurial 

 pump, the spectrum of mercury can be seen. Numerous writers such 

 as Regnault.t Berthellot,^ Ramsay and Young, § Karsten,|| Merget«|[ and 

 McLeod** have all proved the volatility of mercury. Merget in particular 

 has shown that even at a temperature of — 44°, it possesses a sensible 

 vapour tension, while McLeod has been able to estimate the actual 

 ■weight of mercury which existed in the form of vapour in a vessel at 

 the ordinary temperature of the air. In one experiment it was found 

 that in a flask 1'9 litres capacity the weight of mercury vapour was only 

 the very small amount of 0'00009 gi-am. 



In India, where we deal usually with atmospheric temperatures 

 considerably above those where all the published experiments on this 

 subject have been made, it may naturally be expected that the volatility 

 of mercury will be a very appreciable quantity. This fact has lately 

 been proved to me in a very striking way. At Buxar (Bohar) there is 

 a Government Meteorological Observatory where there is a mercurial 

 barometer suspended on the inner wall of a house, but immediately 

 opposite a doorway, and in such a position that though exposed to the 



* Faraday, Soliw. 32 •182, and Pogg. 9, also Watts's Dictionary of Cliomistry, 

 article on Moronry. 



t Compt, rend. Ixxiii. 



j Ditto ditto 100, 13, 26-1328. 



§ Journ. Chem. Soo. Trans. ISSCi, 37-50. 



II Pogg, V, 245. 



IF Compt. rend. Ixxiii, 1356. 

 #* Ohem. NowB, 48, 251, 



