C 204 ] 
of air pretty ftrongly together, in a trough of 
water, or at lealt palled it feveral times through 
the water, from one jar to another, that the lu- 
perfluous fixed air might be abforbed, not fufpedt- 
ingat that time that the agitation could have any 
other effedt ; but having fince 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 rel'piration (and in one particular 
inftance the mere transferring of the air from one 
vefifel to another through the water, though for a 
much longer time than I ever ufed for the mix- 
tures of air, was of confulerable 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 effedfc on the putrid air as, from the genera- 
lity of my obfervations, I fhould have expected. 
I was always aware, indeed, that it might be 
laid, that, the refiduum of fixed air not being very 
noxious, fuch an addition mult contribute to mend 
the putrid air ; but, in order to obviate this ob- 
jedlion, I once mixed the refiduum of as much 
fixed air as. I had found, by a variety of trials, to 
befufficient torelioreagiven 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 lb well as 
it. did with me, and in fo great a number of trials, 
unlefs fixed air have fome tendency to car red! air 
tainted with respiration or putrefadtion ; and it is 
5 perfedlly 
