89 



gas. It forms with oxygen a powerfully explosive mixture, 

 when the volume of the latter is to that of the former, as 

 three or four to one. The new gas explodes spontaneously 

 when brought in contact with chlorine gas ; and this effect 

 is accompanied with the production of flame, and the copious 

 deposition of carbon : and is quite independent of the action 

 of light, or the sun's rays, as it readily takes place in the 

 dark. Under the ordinary pressure of the atmosphere, 

 water absorbs about its own bulk of the gas, which is again 

 liberated by heat, apparently unaltered. 



According to Professor Davy's experiments, the new gas 

 consists of a volume of hydrogen gas and two volumes of 

 the vapour of carbon condensed into one volume ; and it 

 requires for its complete combustion two and a half volumes 

 of oxygen gas. Its specific gravity is 0,917, that of common 

 air being 1.000. 100 cubic inches of it weigh 28.4378 grains. 



The equivalent of the new gas appears to be 13.24, and 

 the formula by which it is expressed is 2c +h, or c^-|-h. 

 The name proposed for it is bicarhuret of hydrogen^ which 

 simply expresses its chemical constitution. 



A paper by Professor Mac Cullagh, '' on the Properties 

 of Surfaces of the second Order," was read. 



Among* various other matters, this paper contains a new 

 class of properties which are analogous to the focal proper- 

 ties of the conic sections. The author has found that sur- 

 faces of the second order may be generated by means of a 

 given point as focus, a given right line as directrix, and a 

 given plane. In general, every such surface is the locus of 

 a point, whose distance from the focus bears a given ratio to 

 its distance from the directrix, the latter distance being 

 measured parallel to the given plane. This mode of gene- 

 ration, however, excludes surfaces of revolution about the 

 major axis, as the corresponding generation of the conic 

 sections excludes the circle. When the given ratio is not 



