1-820.] Royal Academy of Sciences. 377 



it will not yet form prussian blue. Further experiments showed 

 that it contained hydrocyanate and carbonate of ammonia, and 

 also ammonia combined with a third acid which M. Vauquelin 

 calls the cyanic, but without absolutely determining the compo- 

 sition of its radical. 



The water, therefore, is decomposed ; part of its hydrogen com- 

 bines with one part of the cyanogen, and forms hydrocyanic acid; 

 another part unites with the azote of the cyanogen, and forms 

 ammonia ; the oxygen of the water forms carbonic acid with one 

 part of the carbon of the cyanogen. The third acid results from 

 some combination of the same kind, and there still remains some 

 carbon and azote which could not be converted into any of those 

 acids from a deficiency of oxygen, and which produces the 

 brown deposit. 



Alkaline oxides produce similar effects, but much more quickly. 



Cyanogen, treated with a number of other oxides, metals, and 

 combustible substances, afibrded results not less curious to M. 

 Vauquehn. The most interesting question that could be resolved 

 was the inquiry whether prussian blue is a cyanuret or a hydro- 

 cyanate ; that is to say, whether it is a combination of oxide of 

 iron with cyanogen, or rather with its hydro-acid. M. Vau- 

 quelin having found that water impregnated with cyanogen can 

 dissolve iron without changing it into prussian blue, and without 

 the disengagement of any hydrogen gas, and that prussian blue 

 was left in the undissolved portion ; while hydrocyanic acid 

 converts iron or its oxide into prussian blue without the help 

 either of alkalies or of acids ; he has concluded from hence, 

 against the opinion of M. Gay-Lussac, that prussian blue is a 

 hydrocyanate, and that when iron is exposed to water impreg- 

 nated with cyanogen, there is not only formed in it cyanic acid, 

 which dissolves a part of the iron, but also, and at the same 

 time, hydrocyanic acid, which changes another part of the iron 

 into prussian blue. 



He even estabhshes it as a general rule, that those metals 

 which, hke iron, decompose water at the ordinary temperature 

 of the atmosphere, form hydrocyanates ; and that those metals 

 which do not possess this power, as silver and quicksilver, form 

 only cyanurets. 



It is well known that most acids are formed by the com- 

 bination of oxygen with certain substances to which the 

 name of radicals is given, and that the acid thus formed difters 

 in its properties according as there enters into the combination 

 a greater or less proportion of oxygen, and is called by a ditterent 

 name, to which modern chemists have given a certain regularity, 

 indicating the degree of oxidizement by means of the termination. 



It is tluis that azote produces, by successive additions of oxy- 

 gen, nitrous gas, nitrous acid, nitric acid ; and we have mentioned 

 in our Analyses for 181G other coinbniations, which difter in their 

 proportions, di.-scovcred by Messrs. Gay-Lussac and Dulong. 



