DECOMPOSITION OF SULPHATES BY HEAT. 47 



therefore was a mixture of sulphurous acid and oxigen. As 

 the distillation proceeded, it appeared to me, that the quan- 

 tity of sulphuric acid diminished in regard to the oxigen gas 

 and sulphurous acid ; and consequently that less acid es- 

 caped decomposition than at the commencement of the pro- 

 cess. V\ hen nothing more was given out, 1 removed the re- 

 tort from the fire. The oxide had not been fused, and it re- 

 tained some acid ; which proves, that at a higher temperature 

 it would have been decomposed completely. The sul- 

 phurous acid and oxigen gas arose necessarily from the 

 immediate decomposition of the sulphuric acid. The oxide 

 of copper dissolved in fact in nitric acid without eiferves- 

 cence; and it is known, that it does not acquire a higher 

 degree of oxidation in the distillation of its feolphate. The 

 two gasses were to each other in bulk nearly as two to 



one." 



" Though sulphuric acid has long been prepared by dis- Decompositioa 



tillation from sulphate of iron, and this has been an object of "^'"|P^f*^*** 

 . . . , . . "^ iron by heat. 



continual examination, attention has not been paid to seve- 

 ral circumstances presented by its decomposition. It was 

 known, it is true, that the sulphuric acid was always accom- 

 panied with sulphurous acid : but as the iron takes a higher 

 degree of oxidation in this process, it was supposed to give 

 riseto all the sulphurous acid by decomposing the sulphuric, 

 Mr. Chaptal was, I believe, the first, who remarked, that a 

 little oxigen also was obtained. In fact, the sulphate of iron 

 undergoes the same decomposition by heat as the sulphate 

 of copper: only the results are modified by this circum- 

 stance, as the metal is susceptible of a higher degree of oxi- 

 dation, the proportion of sulphurous acid to oxigen gas 

 evolved is greater." 



♦* The sulphates of manganese and zinc have exhibited to Sulphates of 

 me precisely the same phenomena as the sulphate of cop- m^nganeseani 

 per ; and therefore I shall not stop to describe them. 1 

 shall only observe, that the first of these salts may easily be 

 prepared by calcining the black oxide of manganese in a red 

 heat ; for after this it dissolves readily in sulphuric acid." 



*' When concentrated sulphuric acid is made to act on Two sulphates 



tin, antimony, or bismuth, two compounds are formed. °^^*"',*"'^"^?' 

 y-v 11- • 1 1 p • 1 1 "y» "^ bismuth. 



One, whicli is very soluble, retains a great deal of acid, and 



