202 PHILOSOPHICAL TRANSACTIONS. [aNNO 1787. 



Exper. 3. To see if heat would not facilitate the production of air in the 

 globe sheltered from the light, I now removed it from the window, and placed 

 it near a German stove, where I kept it warmed to about 90° of Fahrenheit's 

 thermometer for more than 24 hours ; but this was all to no purpose. The air 

 produced was so exceedingly small in quantity, that it could neither be proved, 

 nor measured, there being only a few detached air-bubbles, which had collected 

 themselves near the top of the globe. The medium heat of the water in the 

 globe exposed in the sun's rays, at the time when it furnished air m the greatest 

 abundance, was about 90*^ Fahrenheit. It was sometimes as high as 96° ; but 

 air was frequently produced in considerable quantities when the heat did not 

 exceed 65° and 70°. 



Exper. 4. Finding by the last experiment that heat alone, without light, was 

 not sufficient to enable silk in water to produce air, I was desirous of seeing the 

 effect of light, without heat on them. To this end, I took the globe b, with 

 its contents, and plunging it into a mixture of ice and water brought it to the 

 temperature of about 50° f. and taking it out of this mixture, and exposing it 

 immediately in the sun's rays, which were very piercing at the time, I kept it in 

 this temperature above 1 hours by the occasional application of cloths, wet in 

 ice water, to the lower part of the globe. Notwithstanding this degree of cold, 

 a considerable quantity of air was produced ; though it was not furnished in so 

 great abundance as when the globe was suffered to become hot in the sun's rays. 



Having thus ascertained the great effect of the sun's rays in the production of 

 the air furnished on exposing silk in water to their influence, my next attempt 

 was to determine, whether this arose from any peculiar quality in the sun's light ; 

 or whether other light would not produce the same effect. With a view to 

 ascertaining this point, I made the following interesting experiment. 



Exper. 5. Having removed all the air from the globe b, and having supplied 

 its place with a quantity of fresh water, so as to render it quite full, I replaced 

 it inverted in its jar, and removing it into a dark room, surrounded it with 6 

 lamps with reflectors, and 6 wax candles, placed at different distances from 3 to 

 6 inches from it, and so disposed as to throw the greatest quantity of light pos- 

 sible on the silk in the water, taking care at the same time that the water should 

 not acquire a greater heat than that of about 90° f. After about 10 minutes, 

 the air-bubbles began to make their appearance on the surface of the silk ; and 

 at the end of 6 hours, there was collected at the upper part of the globe a quan- 

 tity of air sufficient to make a proof of its goodness with nitrous air ; and on 

 trial it was found to be dephlogisticated, and of such a degree of purity, that 1 

 measure of it with 3 measures of nitrous air occupied no more than 1.68- 

 measure. 



I afterwards exposed, to the same light, in small inverted glass jars, filled 

 with water, a fresh-gathered healthy leaf of the peach tree, and a stem of the 



