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 
erystals 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 cn 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 
