1819.] Cyanogen and Hydrocyanic Acid. ; 443 
chlorine, cannot combine directly with metallic oxides; and 
there are formed a hydrogenated acid and oxygenized acid, 
because cyanogen is a compound, while chlorine is simple. _ 
«4. Cyanogen is capable of dissolving iron without forming 
prussian blue. This is proved by the fine purple colour pro- 
duced in the solution by the infusion of nutgalls. But as we 
find prussian blue in the portion of iron not dissolved, it is not 
quite certain that the iron is dissolved by the cyanogen: it is 
more probable that it is by the cyanic acid. On this supposition 
the water must have been decomposed: hydrocyanic acid must 
have been formed which would unite with the iron, and cyanic 
acid which likewise dissolving iron holds it in solution. Perhaps 
ammonia and carbonic acid are likewise formed. 
“5. Hydrocyanic acid forms prussian blue directly both with 
iron and its oxide without the presence either of acid or alkali; 
therefore, prussian blue is a hydrocyanate of iron. 
‘6, Whenever cyadide of potash is-in contact with water, 
ammonia is formed, which combines with carbonic acid formed 
at the same time. Hence it happens, that a great quantity of 
cyadide of potash gives only a small quantity of hydrocyanate ; 
a great part of it bemg changed into ammonia and carbonic acid. 
“7, It appears to result from the preceding experiments, that 
the metals which, like iron, are capable of decomposing water at 
the ordinary temperature, form only hydrocyanates; while those 
incapable of decomposing that liquid form only cyadides: Among 
these last are silver and mercury ; though mercury may possibly 
be an exception. 
“8, Finally, all my experiments confirm the beautiful results 
obtained by Gay-Lussac on the composition of cyanogen and 
hydrocyanic acid ; extending the consequences of them.” 
ArticLe IV. r 
On Parhelia, &c. By William Burney, LL.D. 
(To Dr. Thomson.) 
SIR, Gosport Observatory, Nov.26, 1818. 
I acain take the liberty of sending you some further remarks 
on Parhelia, to show that, with a vaporous atmosphere, they 
may be seen in the open day within a certain altitude, as well as 
early in the morning. I have been lately gratified with a sight 
of the Aurora Borealis, two Paraselenze, and several meteors. 
Descriptions of these rare phenomena I herewith inclose for the 
Annals of Philosophy, should they be deemed deserving of a 
place ; and am, Sir, your obedient servant, 
WittiaAm Burney. 
