102 Messrs. F.and E. Rodgers on certain Metallic Cyanurets. 



aqueous solution of the crystallized red double cyanuret of 

 iron and potassium may be readily decomposed by an alco- 

 holic solution of tartaric acid : the bitartrate of poLash is com- 

 pletely thrown down, and a yellow solution is obtained, which 

 has a" strong acid reaction. 65-89 grains of the crystallized 

 salt are exactly decomposed by 90 grains of crystallized tar- 

 taric acid; but as the red cyanuret is very insoluble in strong 

 alcohol, it is better to use a slight excess of the cyanuret. 

 The red cyanuret employed must be quite free from chloride 

 of potassium. The tartaric acid should be dissolved in alco- 

 hol and then added to the saturated aqueous solution of the 

 double cyanuret. The filtered solution of the hydracid must 

 be preserved in green glass bottles, well protected from the 

 light; but, whatever care is taken, the solution gradually be- 

 comes darker, then assumes a dark green tint, and is at length 

 completely destroyed. 



The solution produces in metallic solutions precipitates si- 

 milar to those produced by the red double cyanuret itself. 

 Like that salt, the hydracid produces a deep blue precipitate 

 in the solutions of the protosalts of iron. The hydracid im- 

 mediately darkens the colour of the solutions of the persalts of 

 iron ; but the solution of the red cyanuret produces no imme- 

 diate change in moderately dilute solutions: gradually, how- 

 ever, it changes the colour to a deep brownish red, and ulti- 

 mately produces a green precipitate. When the hydracid or 

 a solution of the red cyanuret is added to a str6ng solution of 

 the persalts of iron, the final precipitate is a mixture of blue 

 and green. The green precipitate becomes blue at the tem- 

 perature of 212°. If washed and dried without exposure to 

 heat, it becomes a green powder, which is readily decomposed 

 by a dilute solution of potash; peroxide of iron subsides, and 

 the supernatant yellow solution throws down a green precipi- 

 tate from the persalts, and a blue precipitate from the proto- 

 salts of iron. 



Perhaps the hydracid just described may be called the per- 

 ferrocyanic acid, as that term will express the analogy which 

 exists between this compound and the persalts of iron. It is 

 difficult to imagine in what manner the double cyanuret of 

 iron and potassium, which produces green precipitates in the 

 solutions of the persalts of iron, differs from the red double 

 cyanuret. 



12. In a paper published in the Glasgow Medical Journal 

 in the year 1831, Mr. Clarke recommended that hydrocyanic 

 acid should be prepared for medical use by the decomposition 

 of cyanuret of potassium by tartaric acid. This process, slightly 



