1 70 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



heat as sulphate of copper. The results are only modified 

 by this circumstance, that since the metal may take up a 

 higher degree of oxidation, there is liberated relatively more 

 sulphurous acid 1 than oxygen" (p. 219). 



" I took advantage of this decomposition of the sulphates 

 to determine the quantity of oxygen which must be added to 

 sulphurous acid to convert it into sulphuric acid. For this 

 purpose, I distilled over mercury some burnt alum, the base 

 of which neither produces nor absorbs any gaseous principle. 

 I collected gas at different stages of the distillation ; and 

 after taking a carefully measured volume, I washed it with 

 caustic potash and measured the residues. I thus found 

 that 100 parts 



Of the 1st portion contained 32-33 of oxygen. 

 2nd ,, 33-23 



3rd 32-53 



4* ,, 32-64 



Mean . . 32-68 



Since the proportion of the two gases was the same through- 

 out the whole course of the operation, one must conclude 

 that the decomposition of sulphuric acid by heat always 

 takes place in the same way, and that sulphurous acid 

 absorbs almost 0*5 of oxygen in passing to the state of 

 sulphuric acid " (pp. 236 237). 



It was thus shown that sulphuric' anhydride consists of 

 sulphurous anhydride combined with one half its volume of 

 oxygen. Since sulphurous anhydride contained its own 

 volume of oxygen, the proportion of oxygen in sulphuric 

 anhydride was greater in the ratio 3:2. 



B. SULPHURETTED HYDROGEN AND THE SULPHIDES. 



Liver of sulphur. Amongst the earliest discoveries of the 

 alchemistic period was the fact that alkalis possessed solvent 

 properties comparable with those of the acids. Thus Geber 



1 In this passage the names " sulphurous acid " and " sulphuric acid " 

 are used to describe the anhydrides. 



