Mr. Smee on the Ferroscsquicyanurct of Potassiu'm. 195 



cyanic acid, which is speedily decomposed into a pale blueish 

 cyanuret of iron. When, however, further additions of this 

 acid are made, the potassium takes oxygen, forms potassa, 

 deutoxide of nitrogen is evolved, and the solution becomes 

 dark coloured. This liquor, when neutralized with potassa, 

 is found to give no precipitate with the persalts of iron, but 

 forms Prussian blue with the protosalts of, that metal. The 

 rapidity of this change depends upon the heat of the solution, 

 for when warm the effect takes place immediately, whilst on 

 the contrary, two or three days are required at a low tempera- 

 ture. When evaporated, a large quantity of nitrate of potassa 

 is deposited ; and lastly some red crystals are formed. When 

 acid is more used, the ferrocyanate is totally decomposed ; the 

 black mass which is the result has at first a sweet, but afterwards 

 leaves a disagreeable metallic taste upon the palate. This 

 process can never be used advantageously to form the ferro- 

 sesquicyanuret, from the quantity of acid which is required, 

 the degree of nicety which must be employed to effect the 

 change, and the impurity of the salt when obtained. 



The next highly oxygenated acid which we have to examine 

 is the iodic ; this when added to ferrocyanate of potash becomes 

 decomposed, the oxygen passes to the potassium to form, 

 potassa, free iodine is evolved, and the potassa passes to 

 another portion of iodic acid, and is precipitated as the iodate 

 of potassa. The free iodine can be readily removed by agi- 

 tation with a little aether, and in this way a tolerably pure 

 ferrosesqui cyanuret of potassium can be extemporaneously 

 obtained, for the solution contains but little iodate of potassa 

 from its insolubility*. 



Chloric acid operates in the same way as iodic acid, but 

 is more difficult of decomposition, and it requires the ac- 

 tion of heat before the smell of chlorine is exhaled and the 

 red ferrocyanate formed. 



If chlorate of potassa be added to the ferrocyanate, and di- 

 lute sulphuric acid be dropped into the solution, red ferro- 

 cyanate of potash will also be formed. 



Bromic acid will not act upon the ferrocyanate with the pro- 

 duction of the ferrosesquicyanuret, but acts as other acids in 

 forming Prussian blue. 



A great variety of other oxyacids have been tried, but 

 none were found to part with their oxygen. 



When a large quantity of peroxide of manganese in fine 



* This elegant process can be employed with advantage when a small 

 quantity of the salt is suddenly wanted, as it scarcely requires a minute to 

 effect. 



02 



