CHEMICAL SCIENCE. 221 



present, a sulphuret of potassium -would be formed in the cyanide of 

 that metal, from which considerable inconvenience would arise in the 

 employment of the cyanide in chemical analysis, and in its application 

 to the preparations of the gold, silver, and copper solutions employed 

 in the electro-plating processes. When the mixture is melted, as 

 before mentioned, there is at first formed only cyanide of potassium 

 and carbonate of the protoxide of iron ; but this last quickly changes, 

 at the temperature to which it is exposed, into carbonic acid, carbonic 

 oxide, and sesqui-oxide of iron ; and this last, when the cyanide of 

 potassium is melted, becomes converted into metallic iron. It is only 

 by a long sustained heat that the carbonate of protoxide of iron is 

 decomposed, so that long after the decomposition of the ferro-cyanide 

 of potassium, and the formation of cyanide of potassium has taken 

 place, there is still a disengagement of gas. Consequently, the pro- 

 portion of cyanide of potassium, which is simultaneously formed, 

 should entirely depend on the duration of the fusion. The iron which 

 remains after a prolonged fusion of the cyanide of potassium, out of 

 contact of air, being washed with hot water, disengages, when an acid 

 is poured on it, not only hydrogen, but always a little carbonic acid 



gas. 



If we follow the directions given in most chemical works, in which 

 it is stated that the materials must be melted, so that the mass submit- 

 ted to a bright red heat becomes tranquil, only a grey colored pro- 

 duct will be obtained. 



If a closed iron vessel be employed, and the disengaged gases col- 

 lected, it will be seen that in proportion as the temperature rises, the 

 relative proportion between the carbonic acid and the carbonic oxide 

 changes, the latter constantly increasing. It is evident that at a high 

 temperature, one portion of the carbonic acid, which passes through 

 the cyanide of potassium, should be reduced into carbonic oxide, and 

 this reduction, without doubt, extends even in part to the carbonic 

 oxide itself; that is to say, that its carbon is separated, and that this 

 renders the product of a grey color. If we dissolve in cold water 

 some cyanide of potassium completely free from particles of iron, and 

 which has thus become grey, and filter the solution, there remains in 

 the filter a black substance, which, being dried, burns away completely 

 on a slip of platinum, and in fact, possesses all the qualities of char- 

 coal. This carbon, in a state of extreme division, does not separate, 

 either by fusion or repose, from the cyanide of potassium, on account 

 of its feeble specific gravity. If a little of this grey cyanide be added 

 to each new melting, it may be purified from this carbon, and no injury 

 done to the product of the new materials employed, as the iron in 

 separating, withdraws the finely-divided carbon, and leaves the cyanide 

 in a state of purity.- 



\ 



LIQUID GLUE. 



M. DUMOLIN publishes the following article on the preparation 

 and nature of liquid glue, in the Comptes Kendus, Sept., 1852. Chem- 



