ix SULPHUR AND PHOSPHORUS 165 



thereby disclosing an excellent method of separating the 

 gas. 



Priestley describes his observations as follows : 



" When ... I got glass phials with ground stopples, 

 perforated, and drawn out into tubes, such as are represented 

 [in Fig 37], I found that heating the oil of vitriol in them 

 produced no air whatever." 



" But though I got no air from the oil of vitriol by this 

 process, air was produced at the same time in a manner 

 that I little expected, and I paid pretty dearly for the 

 discovery it occasioned. Despairing to get any air from 

 the longer application of my candles, I withdrew them ; 

 but before I could disengage the phial from the vessel of 



quicksilver, a little of it 

 passed through the tube 

 into the hot acid ; when, 

 instantly, it was all filled 

 with dense white fumes, a 

 prodigious quantity of air 

 was generated, the tube 



FIG. 37 STOPPERED FLASK USED BY through which it was 



S5r c^fiS*?"* transmitted was broken into 



many pieces (I suppose by 



the heat that was suddenly produced) and part of the hot 

 acid being spilled upon my hand, burned it terribly, so that 

 the effect of it is visible to this day." 



" Not discouraged by the disagreeable accident above- 

 mentioned, the next day I put a little quicksilver into the 

 phial with the ground stopple and tube, along with the oil 

 of vitriol ; when, long before it was boiling hot, air issued 

 plentifully from it ; and being received in a vessel of quick- 

 silver, appeared to be genuine vitriolic air, exactly like that 

 which I had procured before ; being readily -imbibed by 

 water, and extinguishing a candle in the same manner as 

 the other had done." 



" Copper, treated in the same manner, yielded air very 

 freely, with about the same degree of heat that quicksilver 

 had required, and the air continued to be generated with 

 very little application of more heat. The whole produce 



