f *5* 3 



ritiients were not repeated, as I wifli they might be 

 done, in pure fixed air, extracted from chalk by 

 means of oil of vitriol. 



For every purpofe, in which it was neceffary that 



the fixed air mould be as unmixed as poffible, I 



generally made it by pouring oil of vitriol upon chalk 



and water, catching it in a bladder, fattened to the 



neck of the phial, in which they were contained, 



taking care to prefs out all the common air, and alfo 



the firft, and fometimes the fecond, produce of fixed 



air 3 and alfo, by agitation, making it as quickly as 



I poflibly could. At other times, I made it pafs 



from the phial in which it was generated through a 



glafs tube, without the intervention of any bladder, 



which, as I found by experience, will not long make 



a fufficient feparation between feveral kinds of air and 



common air. 



I had once thought that the readieft method of 

 procuring fixed air, and in fufficient purity, would 

 be by the fimple procefs of burning chalk, or 

 pounded lime-flone in a gun-barrel, making it pafs 

 through the item of a tobacco-pipe, or a glafs tube 

 carefully luted to the orifice of it -, and in this man- 

 ner I find that air is produced in great plenty j but, 

 upon examining it, I found, to my very great furprize, 

 that little more than one half of it was fixed air, 

 capable of being abforbed by water -, and that the 

 reft was inflammable, fometimes very weakly, but 

 fometimes pretty highly fo. Whence this inflam- 

 mability proceeds, I am not able to determine, the 

 lime or chalk not being fuppofed to contain any 

 other than fixed air. I conjecture, however, that it 

 muft proceed from the iron, and the feparation of it 



from 



