194 Sir J. Herscbel 07i increasing the light of an Argand 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 071 a Compound of Fluorine "with 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 ohtaining 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 Magazi?ie and Journal. 



Gentlemen, 

 TPHE 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 ordinar}' use that its loisoer edge shall clear the tipper 

 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 



