Chemical Society. 517 



the corrosion of the iron pot in which the fusion is conducted. 

 Professor Liebig assigns an important place to the sulphur of the 

 sulphate of potasli, usually present to the extent of 12 or 16 per 

 cent, in pearlashes, in effecting this corrosion. In the decomposi- 

 tion of the sulphate of potash by charcoal, bisulphuret of potassium 

 is formed, and cai'bonate of potash. Thus, 

 2 S Oj + 2 K O and 4 C = K S, and K O, C O, with 2 C O, and C O. 



The bisulphuret of iron assumes an atom of iron, either from the 

 sides of the iron vessel or from iron filings which are added ; the 

 double sulphuret thus formed is very fusible, and will consequently 

 be equally diff"used through the melted mass. 



The deficiency of product which frequently occurs in the manu- 

 facture of prussiate of potash is ascribed principally to two causes : 

 1st, to the want of iron in the fused mass. The cyanide of potas- 

 sium is then, instead of being converted into ferrocyanide when . 

 thrown into water, decomposed by the free caustic jjotash when heat 

 is applied to its solution. Uniting with the elements of water, its 

 cj'anogen is converted into formic acid and ammonia : 



N C,,, K and 4H O = Co H O3 -f K O and N H,. 

 This destruction of the cyanide may be avoided by adding iron o^" 

 its sulphuret to the ley, or better, the protosulphate of iron. Another 

 cause of loss of cyanide in the pot itself is pointed out. The bisul- 

 phuret of potassium yields sulphur to the cyanide of potassium, and 

 converts the latter into sulphocyanide of potassium. But if the 

 mixture contain a quantity of iron sufficient to unite with all the 

 sulphur, the formation of sulphocyanide will be prevented. Indeed, 

 sulphocyanide of potassium itself is decomposed by iron at a high 

 temperature, and resolved into sulphuret of iron and cyanide of 

 potassium. It is thus seen that, by increasing the proportion of iron, 

 the formation of sulphocyanide is at once prevented, and sulphuret 

 of iron offered in quantity more than sufficient for its solution after- 

 wards by the cyanide of potassium. The quantity of iron necessary 

 to add in the fusion varies from 12 to 20 per cent., with the pro- 

 portion of sulphate of potash in the potashes used. If a sulpho- 

 cyanide appears in the mother liquors, the proportion of iron must 

 be increased. The only remaining condition for the formation of 

 ferrocyanide of potassium, is the complete exclusion of air during 

 the fusion. Cyanide of potassium cannot be kept in fusion exposed 

 to air without absorbing oxygen, and being converted into cyanate 

 of potash ; hence the advantage which English manufacturers de- 

 rive from tflf'ecling this fusion in close vessels. Cyanate of potash 

 may also be produced by the action of cyanide of potassium upon 

 the sulphate of potash existing in the potashes, sulphuret of potas- 

 sium being at the same time formed. Now cyanate of potash is 

 decomposed, by the application of heat to its solution, into carbonate 

 of potash and ammonia. The annnonia which escapes during the 

 evaporation of the ley may therefore come from this source as well 

 as from the decomposition of cyanide of potassium by potash, already 

 adverted to. 



