106 Royal Irish Academy. 



with hydrogen, forming hydrofluoric acid. Placed over water, the 

 solution (if such) has all the properties of hydrofluoric acid, i. e. acts 

 on glass, reddens litmus, and gives precipitates with lime andbarytes. 

 Placed over dry litmus and Brazil wood paper, the former is reddened, 

 and the latter turned yellow 3 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 on 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 to the vapour of these substances. For this 

 purpose bismuth and palladium at a moderate heat, and gold at a 

 high temperature, aftbrded distinguishing tests. To determine the 

 relative attraction of fluorine for those metals upon which it does not 

 act except at high temperatures, they used as positive poles of a bat- 

 tery of sixty pairs of plates, moistened fluoride of lead, palladium, pla- 

 tinum, gold, and rhodium. The palladium and platinum were always 

 acted upon, the gold occasionally, and the rhodium never ; from 

 which they suppose that fluorine might be obtained in an insulated 

 state, by electrolyzing fluoride of lead in a tube of fluor spar, using 

 rhodium as the positive pole. 



They were unable to repeat M. Baudrimont's experiments in glass 

 or fluor spar vessels*. Supposing that the gas he obtained was an 

 oxide of fluorine, they heated in a dry glass tube iodic acid and flu- 

 oride of mercury ; supposing that since iodine decomposes fluoride of 

 mercury, the oxygen and fluorine being set free from their combinations 

 with oppositely electrical bodies (iodine and mercury), would be in 

 the most favourable condition for combining. On the application of 

 a moderate heat a pale yellow vapour rose in the tube, which did 

 not act on the glass, and bleached litmus. 



Mr. Mallet read a paper " On an hitherto unobserved Structure 

 discovered in certain Trap Rocks in the County of Galway." 



The town of Galway is built upon a part of an immense trap dyke, 

 which extends under the sea and to a considerable distance up Lough 

 Corrib. Large excavations for a dock are now making in this rock 

 at Galway, and aftbrd a convenient opportunity of examining its 

 structure. It separates the limestone on the east (which it tilts up) 

 from the syenite of Cunnemara on the west, (which it overlies or min- 

 gles with.) 



Many fragments of both adjacent rocks are found in an altered 

 state imbedded in the trap 5 which with the tilting of the limestone, 

 prove the deposition a true dyke. 



The mass of the rock consists of greenstone, Sp. gravity 2*87, of a 

 * See Lond. and Edinb. Phil. Mag., vol. ix. p. 149. 



