Professor Draper o?i Tithonized Chlorine. 9 



red colour, and on the sides of the glass towards the light, 

 feathery crystals formed, the tint of which bore a close resem- 

 blance to that of the red prussiate of potash. 



Since the invention of the tithonometer, I have been able 

 to observe more closely the habitudes of chlorine. In the de- 

 scription given of that instrument in the December number 

 (1843) of this Journal, it is recommended to cast aside the 

 first observation, because it never gives an accurate estimate 

 of the true effect. When a mixture of chlorine and hydrogen 

 is exposed, muriatic acid does not immediately form; but a 

 preliminary tithonization is necessary, and then at the end of 

 a certain period contraction begins to take place. 



A tithonometer exposed to the daylight is much too pow- 

 erfully affected to allow of the successive stages of change to 

 be distinctly made out ; the preliminary tithonization is accom- 

 plished so rapidly, that the indications of it are merged and 

 lost in the contraction which instantly follows. It is necessary 

 therefore that we should operate with a small lamp-flame. 



To such a flame I exposed a mixture of chlorine and hy- 

 drogen, and marked the number of seconds which elapsed 

 before contraction, arising from the production of muriatic 

 acid, took place. The first indications of movement occurred 

 at the close of 600 seconds. 



The index then moved through the first degree in 480 seconds 



second ... 165 

 third ... 130 

 fourth .,. 95 

 fifth ... 93 



sixth ... 93 



and continued to move with regularity at the same rate. 



These observations, therefore, prove that a very large 

 amount of radiant matter is absorbed before chemical combi- 

 nation takes place ; and that in the case of chlorine and hy- 

 drogen the total action is divisible into two periods ; the first 

 during which a simple absorption is taking place without a 

 chemical effect, the second during which absorption is attended 

 with the production of muriatic acid. 



The facts which I am endeavouring to set forth prominently 

 in this communication are, — 1st, the preliminary tithonization 

 just discussed ; and 2nd, the persistent character of the change 

 impressed upon chlorine when it has been exposed to the sun, 

 an effect wholly unlike a calorific effect, which would soon 

 disappear. 



By resorting to the tithonometer we obtain information 

 equally distinct upon the second point, that the preliminary 



