230 Prof. Davy on the Action of Nitric and 



ration was immediately due to the action of nitrons acid, or at 

 least to some lower oxide of nitrogen than nitric acid, produced 

 by the deoxidation of that acid, from its giving oxygen to the 

 constituents of a part of the sulphocyanide, whilst the reduced 

 portion of the acid, reacting on the rest, gave rise to the formation 

 of the red compound. That this inference was correct, appeared 

 to be shown by the immediate and much more striking effect 

 which was produced by a portion of the same pure and colour- 

 less nitric acid after it had suffered reduction to some extent by 

 its being made to act on a little alcohol, sugar, or starch, or 

 even by exposure to strong sunlight for a short time before the 

 addition of the sulphocyanide. But what appeared to be still 

 more conclusive as to nitrous acid being the chief agent in the 

 formation of this peculiar red combination were the following 

 facts : — Having prepared nitrite of potash by strongly heating 

 some pure nitre, T found that a little of the salt so obtained, 

 being dissolved in water and mixed with some sulphocyanide of 

 potassium, developed instantly, and without the assistance of 

 heat, an intense blood-red coloration, after the addition of a few 

 drops of pure diluted hydrochloric or sulphuric acid had been 

 added to the mixture to set free the nitrous acid combined with 

 the potash. 



That the production of this red compound, under the circum- 

 stances described, is not confined to the combination of sulpho- 

 cyanogen with potassium, was shown by my obtaining it where I 

 employed other sulphocyanides, as those of sodium, ammonium, 

 and silver, as well as with the hydrosulphocyanic acid itself; so 

 that it is probable that it belongs to all the sulphocyanides, 

 w T hich are either soluble, or the suiphocyanogen of which is 

 capable of liberation when acted on in the manner described. 



As to the reaction which takes place, or the exact nature of 

 this red compound which is formed when nitrous acid thus acts 

 on the sulphocyanides, it is very difficult to determine, owing 

 chiefly to the great instability of this peculiar compound ; for it 

 is no sooner formed than it begins to decompose and disappear, 

 evolving, amongst other gaseous products, the binoxide of nitro- 

 gen, which can be easily recognized by the usual tests for that 

 substance ; whilst the presence of sulphuric acid can be readily 

 detected in the mixture. But though this part of the subject is 

 surrounded with many difficulties, I purpose continuing its in- 

 vestigation in the hope of throwing some additional light on 

 the nature of this interesting reaction. In the meantime, how- 

 ever, the observations I have made appear to me of sufficient 

 interest and importance to be placed on record as having some 

 practical bearings in an analytical point of view ; for many cases 

 may occur in different chemical researches where the production 



