112 M. Gay-Lussac's Observations on some Sulphurets. 



sarily obliges us to admit, that the sulphurets formed on de- 

 composing sulphates by charcoal at a red heat, are not pure 

 protosulphurels ; that they must contain a portion of sulphu- 

 ret which has more than one atom of sulphur, and that, con- 

 sequently, it ought to contain a portion of metal combined 

 with oxygen. It is quite clear, in fact, that if the metal was 

 not in part oxidized previous to the action of acids on the sul- 

 phuret, no sulphur would be precipitated. One may even in- 

 fer the quantity of oxygen combined with the metal by the 

 quantity of sulphur precipitated. The proportions of alkali, 

 protosulphuret, and persulphuret, vary with the temperature. 

 I have found, on decomposing the sulphate of soda by char- 

 coal at a red heat approaching to whiteness, that the quantity 

 of sulphur contained in the hydrosulphuric acid, which was 

 disengaged when the sulphuret was treated by an acid, was 

 5.7 times more than what was precipitated. In another 

 experiment with the sulphate of potash, at a lower tem- 

 perature, I obtained about 4.5 instead of 5.7. This relation 

 ought also to be variable according to the affinity of the metal 

 for oxygen. 



I have shown in my memoir on prussic acid, (Ann. de Chi- 

 mie, vol. xcv. p. 164,) that when an atom of potassium is heat- 

 ed in hydrosulphuric acid, one atom of it is decomposed, its 

 sulphur being appropriated by the metal, which then com- 

 bines with another atom of hydrosulphuric acid. I regarded 

 that combination as a hydrosulphate of the sulphuret of po- 

 tassium, and as long as it remains in a dry state, I think no 

 other view can be taken of it. It dissolves in water without 

 colouring it sensibly, and heated by our acid, it yields two 

 atoms of hydrosulphuric acid without a precipitation of sul- 

 phur, which is a consequence of its composition. 



In dissolving this hydrosulphate in water, it may happen 

 that it does not decompose it or that it does. In the last case, 

 we shall have a bi-hydrosulphate of potash ; for the atom of 

 metal will decompose an atom of water, so as to form another 

 atom of hydrosulphuric acid. By evaporating it to dryness, 

 the compound will return to its former nature. 



This combination is precisely what forms when an alkali is 

 saturated by hydrosulphuric acid, and to which I gave the 



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