196 Mr. Smee on the Ferrosesquicyannret of Potassium. 



powder is added to a solution of the ferrocyanate of potash, 

 and the mixture digested for a considerable time, the ferro- 

 cyanate becomes converted into the ferrosesquicyanuret, and 

 on evaporation crystals of the most beautiful ruby red are 

 obtained. The salt thus procured appears to be very pure. 



If a little dilute sulphuric acid be added to the solution in 

 conjunction with the peroxide of manganese, the action takes 

 place more quickly, but sulphate of potassa is formed, which 

 is a great disadvantage. 



The last process in which nascent oxygen contributes to 

 the formation of ferrosesquicyanuret of potassium, is, perhaps, 

 one of the most elegant, efficient, and simple processes in the 

 whole range of chemistry. This mode I was induced to follow 

 from the consideration, that as nascent oxygen effects a change 

 of the yellow to the red ferrocyanate of potassa, a similar 

 change must be produced by its being subjected to a galvanic 

 current. Accordingly some solution of the salt was placed 

 in a tube bent like a syphon, and at the bottom a piece of tow 

 was thrust, in order that a separation might so far be effected, 

 that the solution on one side could not readily pass to the 

 solution on the other. Having thus completed the arrange- 

 ment, a galvanic circuit was passed through the fluid ; when 

 at the cathode, hydrogen was evolved, and at the anode no 

 oxygen, on the contrary, was given off, but the solution be- 

 came of a dark colour. The dark solution was found to pre- 

 cipitate only the protosalts of iron, and on evaporation de- 

 posited red crystals of the ferrosesquicyanuret, but at the ca- 

 thode potash was discovered. The rationale of this change 

 may be deduced from circumstances attending slight altera- 

 tions of arrangement ; for if on the zinc side of the bent tube 

 a saturated solution of the ferrocyanate be placed, and on the 

 platinum side distilled water, and then the galvanic circuit 

 be completed, potash will appear at the platinode, and red 

 ferrocyanate at the zincode. On the contrary, if the distilled 

 water is placed at the zinc side and the ferrocyanate at the 

 platinum side, potash is left at the platinode, whilst at the 

 zincode no red ferrocyanate is found, but a substance which 

 does not redden litmus paper, and which speedily decomposes 

 into Prussian blue ; this is probably ferrocyanogen. Thus it 

 appears that one equivalent of the yellow ferrocyanate is de- 

 composed, the free potash travels one way and the hydro- 

 ferrocyanic acid the other ; the oxygen unites with the hydro- 

 gen of the acid and sets ferrocyanogen at liberty; this again 

 unites with an equivalent of ferrocyanuret of potassium to 

 form the ferrosesquicyanuret. 





