[ I 7° ] 



plant had been growing in the burned air from the 

 8th of the fame month. Befides, the plant which I 

 have found to -be the moil effectual of any that I 

 have tried for this purpofe is fpinach, which is o£ 

 quick growth, but will feldom thrive long in water. 

 One jar of burned air was perfectly reftored by this- 

 plant in four days, and another in two days. This 

 laft was obferved on the 2 2d of July. In general 

 this effect may be prefumed to have taken place in 

 much lefs time than I have mentioned ; becaufe I 

 never chofe to make a trial of the air, till I was 

 pretty fure, from preceding obfervations, that the 

 event which I had expected mufl have taken place, 

 if it would fucceed at all j left, returning back that 

 part of the air on which I made the trial, and which 

 would thereby neceffarily receive a fmall mixture of 

 common air, the experiment might not be judged 

 to be quite fair ; though I myfelf might be fuffici- 

 ently fatisfied with refpect to the allowance that was 

 to be made for. that fmall. imperfection.. 



rn. 



Of inflammable Air.. 



I have generally made inflammable air in the 

 manner delcribed by Mr. Cavendifb, in thePhilofo- 

 phical Tranfactions, from iron, zinc,, or tin; but 

 chiefly from the two former metals, on account of 

 the procefs being the leaft troubiefome : but when 

 I extracted it from vegetable or animal fubftances, . 

 or from coals, I put them into a gun barrel, to the 

 orifice of which I luted a glafs tube, or the (tern of 



a to- 



