ii 6 Sir Benjamin Thompson’s Experiments 
Experiment N° 28. 
In a large cylindrical jar, of very fine tranfparent glafs, 10 
inches in diameter, and 12 inches high, filled with fpring 
water, I inverted a conical glafs jar, 9I inches in diameter at 
the bottom, and containing 344 cubic inches, filled with the 
fame water ; and expofed the whole 21 days, in a window 
fronting the fouth. 
The quantity of air produced amounted to 40 cubic inches 
and its quality, proved by the teft of nitrous air, gave 1 a + yi 
= 1,87, or 212. 
The water in this experiment furnifhed very little air till the 
feventh day ; but after that time, having a {fumed a faint greenifh 
caft, and a fine greenifh {limy fediment (the green matter of 
Dr. Priestley) beginning to be formed upon the bottom of 
the jar, it began to yield air in abundance, and continued to 
furnifh it in pretty large quantities till about the eighteenth 
day, when it appeared to be exhaufted. 
Why the water fhould turn green in this experiment, and 
not in the laid, I know not ; unlefs it was in confequence of 
the large furface of w r ater in the cylindrical jar, which was ex- 
pofed to the air in this experiment ; or in confequence of the 
fun’s {hining direCtly upon the bottom of the veflel where the 
fediment was formed. 
In the former experiment the bafon in which the jar was 
inverted was but juft big enough to admit the jar ; and as the jar 
was cylindrical, the lurface of the water expofed to the atmo- 
fphere, in the bafon, was but very fmall ; and the bafon being 
very thick, and formed of glafs which, though of the white 
kind, was of an inferior quality, and very imperfectly tranfpa- 
rent, as I have already obferved, the bottom of the bafon,. 
7 where 
