194? Sir J. Herschel on increasing the light of anArgand Lamp 
charcoal was made to pass through a cork inserted in one 
end of the tube, the other platinum wire merely dipped into 
the fused fluoride. On connecting the wires with the battery, 
strong electrolytic action commenced, bubbles of gas were 
evolved rapidly at the surface of the charcoal, which, on ar- 
riving at the surface of the fused fluoride of lead, acted in- 
stantly upon the glass. The litmus paper was not bleached, 
nor the gold-leaf or platinum wire acted upon. Whether 
fluorine would act upon perfectly dry cold glass remains to 
be proved. 
Conclusion , — Fluorine then, when obtained in an insu- 
lated state, is a colourless gas, possessing properties analogous 
in all respects to those of chlorine ; having, like it, strong at- 
trative powers for hydrogen and metals, but inferior to it in 
negative electrical energy. 
2. 'Note on a Compound of Fluorine mth Selenium, 
When the vapour of selenium is passed over fluoride of 
lead fused in the platinum apparatus which I employed in 
obtaining the fluorides of carbon and cyanogen, a seleniuret 
of lead is formed, and crystals similar in form to those of 
fluoride of carbon are condensed in the cold receiver. These 
crystals are soluble in strong hydrofluoric acid. They sublime 
unaltered at a high temperature. They are instantly decom- 
posed by water or acids, in which property they resemble the 
fluorides of sulphur and phosphorus. 
XXXV. On a simple mode of obtaining from a common 
Argand Oil Lamp a greatly increased quantity of Light : in 
a letter from Sir J. Herschel, Bart. 
To the Editors of the Philosophical Magazine and Journal, 
Gentlemen, 
^I^HE following simple, easy, and unexpensive mode of 
greatly increasing the quantity of light yielded by a com- 
mon Argand burner, has been used by me for some years, and 
is adapted to the lamp by which I write, to my greatly increa- 
sed comfort. It consists in merely elevating the glass chimney 
so much above the usual level at which it stands in the burn- 
ers in ordinary use that \is lo*wer edge shall c\eav the upper 
edge of the circular wick by a space equal to about the fourth 
part of the exterior diameter of the wick itself. This may 
be done to any lamp of the kind, at a cost of about sixpence, 
by merely adapting to the frame which supports the chimney 
four pretty stiff steel wires, bent in such a manner as to form 
