1821.] Mr, Deuchar on the Discharge of Ordnance. 449 



deep green colour changing at the same time, and becoming of 

 a lighter green. At a higher temperature it blackens, gives 

 azotic gas, and finishes by deflagrating. The black mass 

 appears to be Fe C* + 2 Co C*, of which a small quantity of 

 carbon is accidentally lost by the presence of an indeterminate 

 quantity of adhering moisture. 



8. Cyanuret of Mercury has been so thoroughly examined by 

 M. Gay-Lussac that I have nothing to add, excepting that the 

 coaly mass which remains after the decomposition of this cyanu- 

 ret is derived from the formation of carburet of mercury during 

 the decomposition, and this is the reason why the cyanogen is 

 always mixed with azotic gas. It is this carburet which renders 

 the mass black, and at last, when exposed to a high tempera- 

 ture, the mercury is volatilized, and the charcoal remains. 



There is also a double cyanuret of iron and mercury, or rather 

 a double hydrocyanate of protoxide of iron and deutoxide of 

 mercury. It is obtained by dropping a solution of corrosive 

 sublimate into one of cyanuret of iron and potassium. A white 

 precipitate is formed ; but it is decomposed not only by ebulli- 

 tion, which causes the cyanuret of mercury to dissolve, and 

 leaves that of iron insoluble, but also by the contact of the air, 

 which causes the cyanuret of iron to become prussian blue ; so 

 that I have not been able to obtain it in a dry state. 



.9. Gi/anuret of Iron and Silver becomes bluish by exposure 

 to a little too much during drying. It is a cyanuret, and not an 

 hydrocyanate. When decomposed, it gives at first cyanogen, 

 and afterwards, when the cyanuret of iron begins to decompose, 

 it gives azotic gas. The phenomenon of combustion occurs at a 

 lower temperature than with other cyanurets. The residual 

 mass is a mixture of metallic silver and quadricarburet of iron, 

 from which the silver may be separated by being well tritu- 

 rated with mercury. 



{To he continued.) 



Article VIII, 



On the Application of Howard's Fulminating Mercury to the 

 Discharge of Ordnance. By John Deuchar, MWS. Lecturer 

 on Chemistry in Edinburgh. 



(To the Editor of the Annals of Philosophy.) 



SIR, EdinUifgh, March 7, 1821. 



I HAVE just read a communication from your correspondent 

 "T'. N. R. M. in the number of the Annals for this month. He 

 seems to have overlooked that part of my paper near the top of 

 page 91, in which I mention that I had used fulminating mercury, 



New Series, vol. i. 2 f ^ 



