880 Prof. Draper on the Allotropism of Chlorine, 



was perceptible, then small bubbles of gas made their appear- 

 ance ; they increased in quantity for a time, but finally the 

 speed of decomposition became uniform. On analysis by de- 

 tonation with hydrogen, after washing out any chlorine con- 

 tained in it, this gas was found to contain 97 per cent, of 

 oxygen. 



III. The rapidity of this decomposition depends on the 

 quantity of the rays and on the temperature. 



In various repetitions of these experiments on different days, 

 I soon convinced myself that the rate of evolution of oxygen 

 depended on the quantity of the rays. Among other proofs I 

 may mention this : after ascertaining the rate of decomposi- 

 tion in the reflected beam, if the bulb be set in the direct sun- 

 shine, the bubbles increase in number, the total quantity of 

 oxygen evolved becoming greater in the same space of time ; 

 an effect obviously due to the difference of intensity of the re- 

 flected and incident beams. When a certain point is gained, 

 apparently no further increase of effect takes place on increa- 

 sing the brilliancy of the light, as I found by employing a 

 convex lens. 



With respect to the influence of temperature. — If, while 

 one of the bulbs is actively evolving gas in the sun's rays, it 

 be warmed by the application of a spirit-lamp, the amount of 

 gas thrown off becomes very much greater : a difference of 

 a few degrees produces a striking effect. As an illustration 

 of this I placed in the sunshine two bulbs which were nearly 

 alike, except that one of them was painted black with India 

 ink on that portion which was furthest from the sun. The 

 rays coming through the transparent part had access to the 

 solution, and then impinging on the dark side raised its tem- 

 perature. On measuring the quantity of gas collected, it was 

 found, — 



In the transparent bulb . . . 3 '46 

 In the half-blackened bulb . . 6"19 



IV. The decomposition of water, once begun in the sun- 

 beams, goes on afterwards in the dark. 



1st. This very important fact may be established in a variety 

 of ways. Thus, if a bulb be removed from the sunshine 

 whilst it is actively evolving gas, and be placed in the dark 

 after the gas has been turned out of it, a slow evolution con- 

 tinuously goes on ; the gas collecting in the upper part of the 

 bulb. 



2nd. A bulb A, fig. 2, having a neck i, the end of which 

 was bent at c upwards at an angle of about 45°, was employed. 

 After exposure to tlie sun, by inverting the bulb and with one 

 finger closing the extremity c, the gas disengaged could be 



