82 Intelligence and Miscellaneous Articles. 



it was attempted to increase the proportion of nitre, but by this the 

 crucible was so much cooled that the ferrate was not formed. — Ann. 

 de Ch, et de Phys., November 1844. 



PREPARATION OF FERRATE OF POTASH IN THE MOIST WAY. 



When a current of chlorine gas is passed into a concentrated solu- 

 tion of potash containing suspended hydrated sesquioxide of iron, M. 

 Fremy states that the liquid soon assumes a fine purplish-red colour, 

 and the sesquioxide of iron is dissolved ; when the potash is greatly 

 in excess, a blackish powder is precipitated ; this is merely ferrate 

 of potash, which is insoluble in the alkali. The ferrate thus precipi- 

 tated carries with it considerable quantities of chloride of potassium ; 

 in order to purify it, it must be dissolved in water and again precipi- 

 tated by concentrated potash. The ferrate of potash cannot be 

 thrown on a filter ; for not only will the excess of potash react upon 

 the paper, but the ferrate would be decomposed by the organic 

 matter. 



Ferrate of potash is to be dried by placing it upon absorbent pieces 

 of porcelain ; when the salt is dry it should be quickly inclosed iu 

 small tubes sealed by the lamp, for the humidity of the air decom- 

 poses it. 



When pure ferrate of potash is required, the sesquioxide of iron 

 should be first precipitated either by ammonia or excess of potash, 

 and then washed and afterwards suspended in a very concentrated 

 solution of potash ; through this the chlorine is to be passed, but 

 not too rapidly ; as the chlorine combines with the potash, and as 

 the ferrate cannot be formed except the liquor be very alkaline, 

 fragments of potash must be occasionally added to supply the place 

 of that which combines with the chlorine. 



The liquid becomes very hot and disengages considerable quan- 

 tities of oxygen [chlorine ?] ; but it was ascertained by M. Fremy 

 that this high temperature does not decompose the ferrate of potash, 

 that being fixed by the excess of potash ; on the other hand, it is 

 inconvenient to employ too great an excess of potash, for a saturated 

 solution of alkali absorbs chlorine with difficulty. 



Properties of the Ferrate of Potash. — When precipitated from its 

 solution by excess of potash, it is black, very soluble in water, and 

 imparts to it a fine reddish-violet tint ; the solution decomposes 

 spontaneously, evolving oxygen, precipitating sesquioxide of iron, 

 and leaving potash in solution ; at a boiling heat this reaction is 

 instantaneous, and this decomposition appears to take place more 

 rapidly under the receiver of the air-pump than at usual pressures; 

 the presence of finely-divided substances also hastens the decompo- 

 sition ; thus a solution remains for some time without showing any 

 signs of decomposition ; but when it has deposited small portions of 

 sesquioxide of iron, the decomposition goes on rapidly, and it can 

 only be stopped by pouring off the solution. Other metallic oxides, 

 such as those of silver and manganese, produce the same, effect: 

 these reactions resemble some of those of oxygenated water, but 

 they jdo not take place with the same intensity, for the metallic 



