300 



from the dissolved contents of the tube by Hme. Is this method 

 preferable to burning it with silica ; conveying the fluosilicic 

 acid into ammonia, and estimating by the weight of silica ?" 



The Secretary read a second notice by the same author, 

 on a supposed fluoride of nitrogen. 



" Having transferred a drop of chloride of nitrogen into 

 a platinum capsule containing a little water, on adding to the 

 water an aqueous solution of fluoride of silver, a gas was 

 freely evolved, somewhat resembling chlorine in smell, but 

 of so pungent a nature, and so exceedingly irritating to the 

 eyes, that I was unable to approach near enough to deter- 

 mine any of its properties, although my eyes were protected 

 by a mask and spectacles. When the gas had all escaped, 

 the capsule was found to contain chloride of silver, fluoride 

 of silver and water, and had not been sensibly heated by the 

 intense chemical action which had taken place. 



*' Again, on adding to a portion of dry fluoride of silver 

 contained in a platinum dish, a drop of chloride of nitrogen, 

 so violent an explosion took place, that the platinum dish 

 was torn as if it had been made of parchment, and a consi- 

 derable part of it blown away." 



Mr. Robert Mallet communicated a notice of the dis- 

 covery of the property of the light emitted by incandescent 

 coke to blacken photogenic paper; and proposed it as a 

 substitute for solar light, or that from the oxy-hydrogen 

 blowpipe with lime. 



One of the most important applications of the photogenic 

 process, as yet suggested, is its adaptation to the self regis- 

 tering of long continued instrumental observations. Unless, 

 however, an artificial light, of a simple and inexpensive cha- 

 racter, can be found to supply the place of solar light at 

 night, the utility of this application will be much limited. 



Few artificial lights emit enough of the chemical rays to 



