4 Professor Draper on Tithonized Chlori7iet 



A mixture of chlorine and hydrogen does not, therefore, 

 instantly give rise to the production of muriatic acid on ex- 

 posure to the light, but as a preliminary condition a certain 

 definite amount of absorption must take place. 



Now if this were a mere molecular disturbance, such as 

 might be brought about by the action of heat, we should ex- 

 pect to find it transient and speedily passing away. Such, 

 however, is far from being the case. As with simple chlorine, 

 so with this mixture, after it has been tithonized it loses its 

 quality very slowly. I have observed that after a week or 

 more has elapsed since it was first exposed to the light, it 

 commences to contract when placed in a feeble gleam. 



IV. Rays are absorbed in producing this change. 



I have thus far assumed that the rays which bring about 

 these changes are absorbed ; the following is the proof which 

 I have to offer : — 



Over a tube half an inch in diameter and six inches long, 

 closed at its upper extremity and open at its lower, invert a 

 jar of the same length and one inch and a half in diameter. 

 Fill the tube and the jar at the salt water trough, about two- 

 thirds full, with the same mixture of chlorine and hydrogen. 

 Expose them to diffuse daylight. Now it is clear that no rays 

 can gain access to the tube, except after having passed through 

 the gaseous mixture in the jar. After a certain space of time 

 the level of the liquid in the jar commences to rise, but that 

 in the tube will remain much longer wholly stationary. 



It therefore appears that a beam which has passed through 

 a mixture of chlorine and hydrogen has lost, to a great extent, 

 the quality of bringing about the union of a second portion of 

 the mixed gases through which it may be caused to traverse. 

 The active rays have been absorbed ; they disappear from the 

 beam, and are lost in producing their first effect. 



A beam of light becomes detithonized in producing a che- 

 mical effect ; the beam, as well as the medium on which it acts, 

 becomes changed. I have a series of results which proves 

 that this takes place for a great variety of compound bodies. 



V. It is the indigo ray iiohich is absorbed. 



As has been said, it is a ray which corresponds in refrangi- 

 bility to the indigo which produces these results. 



In a small porcelain trough I inverted, side by side, ten 

 tubes, each of which was three inches long and one-third of 

 an inch in diameter, the trough being filled with salt water. 

 I passed into each tube a certain quantity of untithonized 

 chlorine and hydrogen. A beam of the sun, being directed 

 by a heliostat into a dark room, was dispersed horizontally 



