338 



" 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 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 chareoal, which, on arriving at the surface 

 of the fused fluoride of lead, acted instantly 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 insulated 

 state, is a colourless gas, possessing properties analogous in 

 all respects to those of chlorine ; having, like it, strong at- 

 tractive powers for hydrogen and metals, but inferior to it 

 in negative electrical energy." 



2. Note on a Compound of Fluorine with Selenium. 

 " When the vapour of selenium is passed over fluoride of 

 lead fused in the platinum apparatus 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 un- 

 altered at a high temperature. They are instantly decom- 

 posed by water or acids, in which property they resemble the 

 fluorides of sulphur and phosphorus." 



The President read a paper, by the Rev. Dr. Robinson, 

 M.R.I.A., &c, on the recent Employment of Rockets to 

 determine the Difference of Longitudes of Armagh and 

 Dublin, and on the proposed Extension of this Operation to 

 other British Observatories. 



In this paper, after alluding to the recommendation of the 



