194- Mr. Smee on the Ferrosesquicyanwct of Potassium. 



firmed by heating the red precipitate in a test tube, when no 

 water is given off; and the latter fact is also proved by the evo- 

 lution of chlorine or bromine, on the addition of two or three 

 drops of strong heated sulphuric acid to a few grains of red salt. 



When heated alcohol is added to this red mass a small por- 

 tion is dissolved, which is again deposited when the spirit is 

 evaporated. This salt by its characters is known to be either 

 the bromide or the chloride of potassium. By this method 

 the red ferrocyanate of potassa, which is insoluble in alcohol, 

 becomes purified ; but this is a troublesome and expensive 

 process, as the bromide or chloride is but little soluble in the 

 spirit, and therefore a large quantity must be used. 



About half an equivalent of chlorine or bromine is required 

 to effect this change, and great care must be employed to 

 prevent excess of these substances, as they are apt to react 

 upon a portion of the salt. The liquid in this case contains 

 Prussian blue dissolved, which materially discolours the salts, 

 and it can only be precipitated from the solution by the ad- 

 dition of neutral salts, as sulphate of soda, which renders the 

 red ferrocyanate impure. In a similar manner, chloride of 

 soda, as might be expected, forms the red ferrocyanate of po- 

 tassa. 



From the foregoing details a knowledge is obtained of the 

 action of chlorine and bromine upon the ferrocyanate, for we 

 have seen that chloride and bromide of potassium is formed, 

 and that one half an equivalent of these substances is necessary 

 for this change. Now it is manifest that half an equivalent of 

 potassium is removed from the ferrocyanate, so that the new 

 salt, instead of consisting of iron one equivalent, potassium 

 two equivalents, cyanogen three equivalents, contains iron 

 one equivalent, potassium one and a half equivalent, cyanogen 

 three equivalents ; and therefore it is rightly named the 

 ferrosesquicyanuret of potassium : that half an equivalent 

 of potassium has been removed from the salt, two or three 

 experiments have verified. 



The acids as a class will not effect a similar change, be- 

 cause as they combine not with potassium but with potassa, 

 water must be decomposed, the oxygen uniting with the metal, 

 and the hydrogen passing to the ferrocyanate, forming hydro- 

 ferrocyanic acid. 



A question naturally arises whether the potassium may 

 not be removed from the ferrocyanuret by other processes, 

 and we are led to try the action of the anions, and of these 

 I attempted to add oxygen to the salts by the use of nitric 

 acid. This acid, when added in small quantities to the yellow 

 ferrocyanate, acts as the other acids by liberating hydroferro- 



