on the Production of Dephlogijlicated Air\ m 
% 
The water in both thefe experiments had acquired a faint, 
greenifh cad ; but the colour of that with the cotton was 
rather the deeped. 
Upon examining this water under a microfcope, I found it 
contained a great number of , animalcules, exceedingly final!, 
and of nearly a round figures That with the filk contained t 
the fame: kind of animalcules dikewife, but not. in- fo great 
abundance. I never failed to find them in every cafe in which- 
the water .ufed in an experiment had acquired a greenifh hue; 
and from their prefence alone, I think it more than probable, 
that the colour of ^the. water, in the firf in/tance^ arofe in alt: 
cafes. I have.fpent a great deal- of time in obfer.ving them, 
and have made many experiments upon their produdtion ; but 
as- 1 have not yet been able to fatisfy my own mind, with \ 
refpebt to the part they a£t in the operation of purifying the air. 
in water, I (hall not add to the length of this letter by giving 
an account of my enquiries and obfervations refpe&ing them. 
I ’was yet by* no means fatisfied with refpebf to the part r 
which the filk and other bodies, expofed in water in the fore-' - 
going experiments, adfed in the purifying or dephlogiflicating ; 
of the air produced. 
Dr. Priestley has long fince difeovered, that many animal- 
and vegetable fubftances putrefying, or rather diffolving, ia 
water, in the fun, caufe the water to yield large quantities of 
dephlogifticated air ; but I could hardly conceive, that the 
fmall quantity of filk which was ufed in my experiments, and* 
which had been conftantly in water for more than three 
months, and had fo often been wafhed, and even boiled ia. 
water, fhould yet retain a power of communicating any thing 
to the large quantities of frefh water in which it was fuccef- 
fively placed ; at leaft any thing in fufficient quantities to impreg-. 
nate 
