Professor Draper on Tithonized Chlorine. 7 



in the green than in the yellow, in the yellow than in the 

 orange, in the orange than in the red ; and, had the expo- 

 sure to the spectrum been long enough, the liquid in every 

 one of the tubes would have risen. 



VIL The indigo ray forms the muriatic acid as well as pro- 

 duces the prelimifiary tithonization. 



It only now remains to inquire, whether the rays which 

 cause the production of the muriatic acid are those which 

 effect the tithonization of the chlorine; in other words, whether 

 the first stage of the process is brought about by the same 

 agent which carries on the second. The experiment which I 

 have just described shows that tithonization is most actively 

 produced by the indigo ray, and it is easy to show that it is 

 the same ray which carries on the second part of the process; 

 for, if before placing the tubes in the prismatic spectrum we 

 tithonize them in the daylight, so that the liquid has just com- 

 menced to rise in each, and then expose them to the spectrum, 

 it will be found that the tube in the indigo rises most rapidly, 

 and the others in the order stated before. Therefore we per- 

 ceive that the same ray commences, carries on, and completes 

 the process. 



Few substances can exceed in sensitiveness to light a mix- 

 ture of chlorine and hydrogen previously tithonized. Brought 

 into the obscure daylight of a gloomy chamber, it is remark- 

 able how promptly the level of the liquid in the tube rises ; 

 how, when the shutters are successively thrown open, the ac- 

 tion becomes more and more energetic; and how, in an in- 

 stant, it stops when the instrument is shaded by a screen. 



I have not recorded in this- communication a multitude of 

 experiments of detail which go to support the conclusions 

 here drawn, and which will be published at a proper time. It 

 has been my object on this occasion to call attention to the 

 fact, that chlorine, an elementary body, undergoes a change 

 after exposure to the light; a change which appears to pro- 

 duce an exaltation of its electro-negative properties, as is shown 

 by its power of uniting more energetically with hydrogen. 

 This change must not be confounded with those transient ele- 

 vations of activity due to increased temperature, inasmuch as 

 this is more permanent in its character. It arises from the 

 absorption of rays which exist most abundantly in the indigo 

 space of the spectrum. That the phaenomenon is due to a true 

 absorption is fully shown in the circumstance, that a beam 

 which has produced this effect has lost the quality of ever after 

 producing a similar result. This is borne out by what we ob- 



