198 Mr. Sraee on the Ferrosesquicyanurel of Potassium, 



than a wide vessel. If this explanation is correct, the action 

 of phosphorus must be classed with the other oxygenating 

 substances, for oxygen, and not phosphorus, removes the 

 potassium*. 



No mode of abstracting the half equivalent of potassium by 

 sulphur is known, for if half an equivalent of sulphur be heated 

 with powdered ferrocyanuret, the ferrosesquicyanuret is not 

 produced, and the alcoholic or terebinthine solution of sul- 

 phur, added to a solution of the ferrocyanuret, also failed to 

 produce this change. Even nascent sulphur arising from the 

 decomposition of sulphuret of potash by an acid did not pro- 

 duce any effectf . 



A current of cyanogen gas passed through a solution of the 

 salt is gradually absorbed, and it becomes of a very dark 

 colour, but red ferrocyanate is not formed. 



Doubtless many may be surprised that the action of iodine 

 has not been adverted to before, and more especially that it 

 should not have been mentioned with chlorine and bromine, 

 as to these it has a striking analogy in most of its properties ; 

 but in reality little resemblance exists between the action of 

 iodine on the ferrocyanate of potassa, and that of chlorine 

 and bromine, as we shall immediately see. If iodine is added 

 to a solution of the salt it speedily becomes dissolved, the so- 

 lution turning to a dark red, and gives a blue precipitate with 

 salts of either oxide of iron. One equivalent of ferrocyanate 

 of potash dissolves about one equivalent of iodine, which re- 

 mains in great part uncombined in solution. If the solution 

 is allowed spontaneously to evaporate the free iodine passes 

 off, and a whitish uncrystallized mass is obtained which has 

 no free iodine, but hydriodate of potassa in its composition. 

 This gives a precipitate with both oxides of iron. Now there 

 is a ready method of ascertaining how much iodine the ferro- 

 cyanate will not only dissolve, but combine with, and for this 

 purpose a definite quantity of the salt is to be dissolved in a 

 small quantity of water, and then placed in a phial. Upon the 

 solution aether is to be poured, then the iodine is to be added 

 gradually, when as soon as the aether is discoloured the satu- 

 ration is known to be effected. Brisk and continued agitation 

 must follow each addition of the iodine, in order that the 

 aether may part with any iodine previously to the point of 

 saturation. When evaporated to dryness more of the iodine 

 is evolved, but still hydriodate of potash may be abstracted 

 from the mass by alcohol. When all the iodine is removed 



* No change takes place if the phosphorus is completely under the solu- 

 tion of the salt. 



f It is foreign to this page to describe the sulphocyanuret of potassium. 



