1 92 Experiments on the Production of Air 



Before I enter upon the detail of my experiments, it 

 will be necessary to premise that I shall in general con- 

 fine myself merely to the facts as they present them- 

 selves, without applying them to the confirmation or 

 refutation of the theories of others, and without entering 

 into any speculative inquiries relative to their remote 

 causes; and in describing the different appearances J 

 shall make use of the most familiar terms. Thus, in 

 speaking of the air produced upon exposing raw silk 

 in water to the action of light, I shall sometimes men- 

 tion it as being yielded by the silk; and I shall some- 

 times speak of the air furnished by exposing water, 

 which has previously turned green in the sun's rays, as 

 being immediately produced by the water, though it is 

 probable that the green matter acts a very important part 

 in the production of this air in the one case and perhaps 

 in the other. But how it acts is not well ascertained ; 

 and I had in general much rather confine myself to a 

 simple and even an unlearned description of facts, than, 

 by endeavouring to give more precise definitions, at first, 

 to involve myself in all the 'difficulties which would 

 attend an attempt to account for phenomena whose 

 causes are but very imperfectly known. 



Experiment No. i. 



My first object was to collect a sufficient quantity of 

 the air, separated from water by silk, to determine its 

 goodness by the test of nitrous air; and to this end hav- 

 ing filled with clear spring-water a globe of thin, white, 

 and very transparent glass, 4^- inches in diameter, with a 

 cylindrical neck f of an inch in diameter, and about 12 

 inches long, I introduced into it 30 grains of raw silk, 

 which had been previously washed in water in order to 





