102 M. Vogel on [Fes. 
The reason why M. Grotthuss’s process is unsatisfactory is, 
that the mixture of prussiate of potash and sulphur is exposed 
to too high a temperature ; for I have ascertained that whenever 
this mixture is exposed to a red heat, or to the heat of a forge, 
as Grotthuss prescribes, potash is disengaged, and sulphuretted 
hydrogen formed. I have, therefore, varied the experiment, and 
have found that a pure sulphuretted chyazate may be formed by 
modifying the heat a good deal. 
For this purpose, a mixture of equal parts of prussiate of 
potash and flowers of sulphur is put into a glass matrass, which 
is exposed to heat. After the matter has ceased to emit air 
bubbles, it is left for an hour in a state of fusion ; but at a tem- 
perature greatly belowa red heat. The matrass is then allowed 
to cool, it is broken in pieces, the black matter is reduced to 
powder, and hot water is poured upon it.* The filtered liquor 
is colourless, perfectly neutral, and contains no sulphuretted 
hydrogen. It is not altered when mixed with proieeunhas of 
iron, and becomes red when mixed with persulphate of iron. If 
the filtered, colourless solution be left exposed for some time to 
the open air, or if it be placed in contact with nitrous acid in 
vapour, it becomes dark red, because it contains protoxide of 
iron combined with sulphuretted chyazic acid and potash. The 
newly prepared liquid, when mixed with ammonia, allows the 
green hydrate of iron to precipitate ; while prussiate of potash 
throws down prussian blue. . ‘ 
When the object in view is to obtain sulphuretted chyazic 
acid, this oxide of iron occasions no obstacle. But if we wish 
to get a pure sulphuretted chyazate, we must drop into the solu- 
tion caustic potash till the whole iron is precipitated, The 
liquid is then filtered while still hot, and evaporated to dryness. 
The salt obtained is very soluble in alcohol. It does not 
become red when exposed to the air; but it is very deliquescent, 
and ought, therefore, to be immediately put into a well stopped 
bottle. The process for obtaining pure sulphuretted chyazate of 
potash may, therefore, be reduced to this : 
Keep a mixture of equal weights of prussiate of potash in 
powder and flowers of sulphur in fusion in a matrass for an hour. 
When the mass has cooled and been reduced to powder, treat it 
with twice its weight of distilled water, and into the distilled 
solution drop nome as long as any precipitate falls. Filter a 
second time, and evaporate the liquid to dryness. 
Extraction of Sulphuretted Chyaxic Acid. 
After having obtained a pure sulphuretted chyazate, it is 
possible to procure likewise a pure sulphuretted chyazic acid. 
* To determine whether the mass has been kept a sufficient time in a state of 
fusion, and whether all the common prussiate of potash has been decomposed, 
dissolve a little of it in water, and try the solution with sulphate of iron. Ifno 
prussian blue is formed, the decomposition is complete. If itis, we must treat 
the powder with boiling alcohol, or fuse it a second time, 
