55 



can be moved. On the slab are four small depressions, in 

 which are placed the substances upon which the action of 

 the gas is to be observed, and over which the receivers, 

 when filled with the gas, can be slid. In opposite sides 

 of these receivers are drilled holes, into which are fitted, 

 air tight, clear crystals of fluor spar, through which the 

 colour of any gas in the receiver may be distinctly observed. 

 The vessels are supported on a stand over a lamp. 



On heating pure fluoride of mercury in these vessels with 

 dry chlorine they obtained a colourless gas, (as seen through 

 the fluor,) having a heavy smell not pungent or irritating, and 

 thereby easily distinguished from chlorine or hydrofluoric 

 acid. When exposed to the air, it does not fume, as 

 would be the case were the slightest trace of hydrofluoric 

 acid present. The inside of the vessel is found coated with 

 crystals of corrosive sublimate. The gas does not extinguish 

 ignited phosphorus or red hot iron wire, and consequently 

 is (as Sir H. Davy conjectured) a supporter of combustion. 

 It detonates with hydrogen, forming hydrofluoric acid. 

 Placed over water, the solution (if such) has all the proper- 

 ties of hydrofluoric acid, i. e. acts on glass, reddens litmus, 

 and gives precipitates with lime and barytes. Placed over dry 

 litmus and Brazil wood paper, the former is reddened, and 

 the latter turned yellow ; in no instance are they bleached. 

 When a receiver of the gas is placed over wet glass, the glass 

 is strongly acted upon; when the glass is carefully dried, 

 the action is not so strong as before. When a small piece 

 of dry glass is placed in a perforation in the interior of the 

 receiver, the glass is acted upon, but not more so than when 

 fluoride of mercury alone is in the vessel, from which they 

 conclude that fluorine does not act on perfectly dry glass. 



To ascertain the action of the gas en metals they found 

 it necessary to try the separate effects of hydrofluoric acid, 

 sublimed fluoride of mercury, and bichloride of mercury, in 

 order to distinguish the action of fluorine from that due 



