48 



DECOMPOSITION OF SULPHATES BY HEAT. 



Actirn of heat 

 on them. 



Products of 

 suljjhates re- 

 taining the 

 acid in weaker 



degrees. 



Those that 

 retain it very 

 lorcibiy exa- 

 mined. 



Sulphate of 

 silver. 



Sulphate of 

 mercury. 



very little oxide: the other, on the contrar}', is formed of 

 much more oxide than acid, and has little solubility." 



*' If the first of these compounds be distilled, the sulphu- 

 ric acid is volatilized as if it were alone: but if the becoiid, 

 in which the sulphuric acid is more strongly retained, be 

 subjected to distillation, oxigen gas and sulphurous gas are 

 evolved." 



** The salts that have hitherto been examined have 

 yielded different products, according to the strength with 

 which the sulphuric acid is combined in them. When it is 

 feebly retained, and has undergone no condensation, it is vo- 

 latilized by heat as ifit were alone, without being decomposed^ 

 If it be retained more forcibly, part only escapes decomposi- 

 tion, and the other part is converted into oxigen and sul- 

 phurous acid gasses. The insoluble sulphates, in which 

 there is no sign of acidity, appearing to retain the acid with 

 great force, it is essential to know what is the action of heat 

 on them." 



*' I put some sulphate of silver into an uncoated glass re- 

 tort, furnished with a tube for collecting the gas. When it 

 began to grow red, the salt melted, but was not decomposed. 

 Having taken it out, I exposed it to a more violent fire in a 

 stone retort ; and then a great deal of oxigen gas was evolved, 

 mixed with sulphurous acid, as Mr. Fourc.oy announced. 

 I did not perceive any dense white fumes as in the preceding 

 experitnents, because very little sulphuric acid was given 

 out. When the process was finished, I found in the retort 

 a button of silver completely reduced. Thus the sulphate 

 of silver is decomposed by heat like the other sulphates, but 

 it gives out more oxigen than they ; on the one hand, in con- 

 sequence of the reduction of the metal, on the other, because 

 it yields very little sulphuric acid." 



" I afterward prepared some sulphate of mercury, by 

 precipitating nitrate of mercury little oxided with sulphate 

 of soda. The precipitate, washed and dried, was exposed 

 to heat in an uncoated glass retort. Scarcely had this begun 

 to grow red, when the salt entered into fusion, and it was 

 soon decomposed. Very little sulphuric acid passed over; 

 and mercury sublimed, with a little sulphate. The other 

 products were sulphurous acid and oxigen gasses mixed in 



the 



