from Water exposed to Light. 219 



shall not add to the length of this paper, by giving an ac- 

 count of my inquiries and observations respecting them. 



I was yet by no means satisfied with respect to the 

 part which the silk and other bodies, exposed in water in 

 the foregoing experiments, acted in the generation of the 

 air produced. 



Dr. Priestley has long since discovered that many ani- 

 mal and vegetable substances, putrefying, or rather dis- 

 solving, in water in the sun, cause the water to yield large 

 quantities of dephlogisticated air ; but I could hardly con- 

 ceive that the small quantity of silk which was used in 

 my experiments, and which had been constantly in water 

 for more than three months, and had so often been 

 washed, and even boiled in water, should yet retain a 

 power of communicating anything to the large quantities 

 of fresh water in which it was successively placed, — at 

 least, anything in sufficient quantities to impregnate those 

 bodies of water, and to cause them to yield the great 

 abundance of air which they produced. 



It was still more difficult to account for the pure air 

 produced in the experiments with wool and fur and hu- 

 man hair ; especially, as in some of these experiments 

 the water had not sensibly changed colour, nor did it 

 appear to have lost anything of its transparency. It is 

 true, in these cases, the quantities of air produced were 

 very small ; but yet its quality was better than that of 

 common air, and considerably superior to that of the air 

 commonly existing in the water, previous to its being 

 exposed to the action of the sun's light. In short, it 

 was dephlogisticated in the experiment ; but the manner 

 in which this was done is very difficult to ascertain. 



With a view to throwing some new light upon this in- 

 tricate subject, I made the following experiments. 



