,. 



SULPHURIC ACID. 163 



moistened with nitric acid. The gaseous sulphurous 

 acid obtains oxygen from the nitric acid, which is rich 

 in this element, and very liberal of it, and thereby be- 

 comes sulphuric acid. A little water, previously placed 

 in the bottom of the vial, absorbs the acid 

 thus formed. To acidify the water to any 

 considerable extent, it will be necessary to 

 burn sulphur, and introduce the moistened rod 

 repeatedly. That the acid is not the sulphu- 

 rous or the nitric acid, employed in the pro- 

 cess, may be proved by using it to make hy- 

 drogen gas. 



392. REMARK. The red fumes which 



What causes . 



the red fumes nil the vial m the last experiment, consist 



of the changed nitric acid, (nitric oxide,) 

 which has just given up part of its oxy- 

 gen, and is now resuming part of it from the air. It 

 thereby becomes a third substance, of a red color, to 

 be again mentioned in the section on nitric acid. 



393. MANUFACTURE OF OIL OF VITRIOL. 



Explain how . 



sulphuric acid The method of the production of oil 

 lurcd^ ^ v i tr il on a l ar ge scale, is essentially the 

 same as that above given. Fumes of 

 burning sulphur, and vapor of nitric acid, with air and 

 steam, are introduced into a leaden chamber, when the 

 process proceeds, as before described. 



394. Comparatively little nitric acid is 



Why is but 



little nitric needed in the process, for it is found that 

 acid required wn jj e ft y^ids oxygen to the sulphurous 

 fumes, the changed acid greedily seizes oxygen from 

 the air of the chamber, arid imparts it again, to keep up 



