I 204 ] 



of air pretty ftrongly together, in a trough of 

 water, or at leaft palled it feveral times through 

 the water, from one jar to another, that the fu- 

 perftuous fixed air might be abforbed, not fufpect- 

 ingat that time that the agitation could have any 

 other effect ; but having iince found that very vio- 

 lent, and efpecially long continued agitation in 

 water, without any mixture of fixed air, never 

 failed to render any kind of noxious air in fome 

 meafure fit for refpiration (and in one particular 

 inftance the mere transferring of the air from one 

 veflel to another through the water, though for a 

 much longer time than I ever ufed for the mix- 

 tures of air, was of confiderable ufe for the fame 

 purpofe) ; I began to entertain fome doubt of the 

 efficacy of fixed air, for that purpofe. In fome cafes 

 alfo the mixture of fixed air had by no means fo 

 much effect on the putrid air as, from the genera- 

 lity of my obfervations, I mould have expected. 



I was always aware, indeed, that it might bo 

 laid, that, the reliduum of fixed air not being very 

 noxious, fuch an addition mull contribute to mend 

 the putrid air ; but, in order to obviate this ob- 

 jection, I once mixed the reliduum of as much 

 fixed air as I had found, by a variety of trials, to 

 be fufficient to reftore a given quantity of putrid air, 

 with an equal quantity of putrid air, without mak- 

 ing any fenfible melioration of it. 



Upon the whole, I am inclined to think that 

 this procefs could hardly have fucceeded fo well as 

 it did with me, and in fo great a number of trials,, 

 unlefs fixed air have fome tendency to correct air 

 tainted with refpiration or putrefaction ; and it is 

 5 perfectly 



