VOL. LXXVII.] PHILOSOPHICAL TKANSACTIONS. 201 



after which I suffer it to stand at rest, while I prepare another measure of 

 nitrous air, which commonly takes up about 20 seconds. 



The measure of the eudiometer being filled with air, I suffer it to remain 

 quiet under water 15 seconds, or while I can leisurely count 30, in order that 

 the air may have time to acquire the temperature of the water in the trough, and 

 that the water in the measure may have time to run down from the sides of the 

 glass tube ; and in shutting the slider I take care to bring it to be exactly even 

 with the surface of the water in the trough. Similar precautions are also made 

 use of, in measuring the volume of the two airs in the tube of the eudiometer, 

 after they have been mixed and diminished in the phial. In order to know 

 when I have added nitrous air enough to the air in the phial, so that the volume 

 of the two airs may amount to 1 measure, and may not be greater than 2 mea- 

 sures, there are 2 marks on the phial, made with the point of a diamond, the 

 one showing 1 measure of the eudiometer, the other showing 2 measures. 

 The tube of my eudiometer is half an inch in diameter internally, and 1 mea- 

 sure occupies 34- inches in length on it, and the measure itself is made of a 

 piece of the tame tube. Both the one and the other are ground with fine 

 emery on the inside, in order to take off the polish of the glass, and by that 

 means facilitate the running down of the water, which might otherwise hang in 

 drops on the inside of the tube on the introduction of air. The nitrous air was 

 always fresh made, and of the same materials, viz. fine copper wire dissolved in 

 smoking spirits of nitre, diluted with 5 times its volume of water, and all pos- 

 sible attention was paid to every other circumstance that could contribute to the 

 accuracy of the experiments. 



Exper. 2. Finding that the quantity and the quality of the air produced 

 depended, in a great measure, on the intensity of the light by which the water 

 and the silk were illuminated, I was desirous of seeing whether, by depriving 

 them entirely of all light, they would not at the same time be deprived -of the 

 power of furnishing air. To ascertain this fagt, I took a globe a, similar 

 to that used in the foregoing experiment, and having filled it with fresh spring 

 water, I introduced into it 30 grains of raw silk, and placing it with its cylin- 

 drical neck inverted in a jar filled with the same water, I covered the whole with 

 a large inverted earthen vessel, and exposed it, so covered up, for several days 

 in my window, by the side of another globe b, containing a like quantity of 

 water and silk, which I left naked, and consequently exposed to the direct rays 

 of the sun. The result of this experiment was, that the water and silk in the 

 globe exposed to the sun's rays furnished air in great abundance, as in the 

 experiment before-mentioned ; while that in the globe covered up in darkness, 

 produced only a few very inconsiderable air-bubbles, which remained attached to 

 the silk. 



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