193 
Mr. G. J. Knox’s Researches on Fluorine. 
the action was allowed to continue for the space of two hours ; 
at the end of which time the litmus was found to be reddened, 
and the gold not acted upon, but a large quantity of sub- 
fluoride of iron formed. 
In the next experiment I made use of a piece of char- 
coal, from which the iron had been removed by boiling it in 
nitric acid ; in this experiment there was no subfluoride ot 
iron formed, but the vessel was found to contain fluosilicic 
acid gas. 
In a third experiment a piece of charcoal was employed, 
which had been previously freed from all metallic impurities 
and from silica, by being first boiled in pure nitric acid, and 
afterwards in hydrofluoric acid. Employing this purified 
charcoal as the positive electrode, I obtained no immediate 
action upon the litmus paper; but after the action had con- 
tinued for two hours, it was found to be completely bleached, 
while the gold had undergone no sensible action. That the 
bleaching was not due to the action of the vapour of hydro- 
fluoric acid was ascertained, by leaving litmus paper for se- 
veral hours in the neck of a platinum retort, from which hy- 
drofluoric acid was distilling. 
The battery was now kept in action for fifteen hours, at 
the end of which time the vessel being examined, the litmus 
had disappeared, and the gold-leaf showed signs of having 
been strongly acted upon, having assumed a dark brownish 
colour, and having gathered itself into little balls, as if it 
had undergone the action of heat. The platinum wire was 
acted upon in those parts where it was in contact with the 
charcoal, but nowhere else. 
When the platinum wire forming the positive electrode 
passed through the stopper to the bottom of the vessel, the 
hydrogen, in place of rising through the perforation in the 
stopper, as in the former instance, rose now into the receiver, 
where, upon applying a light, it exploded, showing that it 
does not enter into combination with fluorine without the aid 
of heat. The presence of the vapour of hydrofluoric acid in 
the vessel prevented me from determining by other experi- 
ments how far fluorine was a supporter of combustion. 
To determine the colour of the gas, a stopper of fluor- 
spar similar to the former was made to fit one of the trans- 
parent fluorspar receivers formerly described. The gas 
evolved in the receiver appeared colourless. 
As the action of the gas upon glass could not be deter- 
mined, owing to the presence of the vapour of hydrofluoric 
acid, I fused in a bent tube of German glass (such as is used 
in organic analysis) fluoride of lead. The wire holding the 
Phil. Mag. S. 3. Vol. 16. No. 102. March 184<0. O 
