from Wate7^ exposed to Light. 211 



insf six hours of sunshine it furnished iAtt cubic inches, 

 which, proved with nitrous air, gave \ a -\- i^n :=. 1.15, 

 or 285. 



The two following days {viz. the 19th and 20th of 

 June), it furnished i iVo cubic inch of air, which, proved 

 with nitrous air, gave \ a-\- i^n ^=. 1.37, or 263 ; after 

 which it totally ceased to yield air, though exposed for 

 several days in the sun's rays. 



Total quantity of air produced, Iy^-^ cubic inches; 

 mean quality, \ a -\- i^n ^=. 1.46, or 254. 



By this experiment it appears that raw silk, when used 

 for the first time, does not immediately dispose the water 

 to yield pure air ; on the contrary, that it phlogisticates 

 the air yielded by water to a very considerable degree ; 

 and this I afterwards found to be the case with several 

 other substances. 



Though the quality, at a medium, of the air furnished 

 in this experiment was not quite so good as that fur- 

 nished in the two experiments last mentioned {yiz. No. 

 13 and No, 14), yet its quantity, in proportion to the 

 quantity of water made use of, was greater than in either 

 of them ; it amounted to something more than one eighth 

 of the volume of the water. 



Of all the substances I had hitherto made use of in these 

 experiments, raw silk had furnished the greatest quantity 

 of pure air, or, to express myself more properly, had 

 caused the water to furnish the greatest quantity ; but it 

 appeared to me very probable that some other body 

 might be found that possessed this property in a still 

 greater degree than silk. Turning this matter in my 

 mind, it occurred to me to make the experiment with the 

 silky, or rather cotton-like, substance produced by a cer- 

 tain species of the poplar-tree, Populus nigra, very com- 



