173 



and muriatic acids there remained insoluble a small quantity 

 of a brownish colour, which, when fused with carbonate of 

 potash, gave of silica 0.10. The solution, supersaturated 

 with potash, filtered, neutralized, evaporated to dryness, 

 gave of silica 1.450; sum total of siHca 1.550. 



From these experiments, together with those of Sir Hum- 

 phrey Davy mentioned above, one might infer that nitrogen 

 is either a compound of silicon and hydrogen, or of silicon, 

 hydrogen, and oxygen ; to determine which, synthetically, a 

 current of dry muriatic acid gas was passed over siliciuret 

 of potassium (formed by heating silica with potassium), 

 placed in a bent tube of Bohemian glass, the extremity of 

 which dipped into a cup of mercury, lying on the bottom of 

 a vessel filled with water. The atmospheric air had been 

 previously expelled from the apparatus by a current of 

 hydrogen. 



The gases insoluble in water having been collected, were 

 found, on examination, to be hydrogen and nitrogen, the 

 relative proportions of which varied in different experiments. 



In two experiments the proportions of hydrogen to ni- 

 trogen were four of the former to one of the latter. 



In a third experiment, as six of hydrogen to one of 

 nitrogen. 



In a fourth, as five of hydrogen to four of nitrogen. 



Observation. — White fumes appeared occasionally in the 

 tube, indicating the presence of muriate of ammonia. 



Professor Lloyd exhibited a specimen of Rock from Terre 

 Adele. 



Professor Mac Cullagh communicated to the Academy a 

 very simple geometrical rule, which gives the solution of the 

 problem of total reflexion, for ordinary media and for uni- 

 axal crystals. 



p 2 



