282 



MODIFIED CHLORINE. 



[MEMOIR XIX. 



phosphorus became of a deep blood -red color, and on 

 the sides of the glass towards the light feathery crystals 

 formed, the tint of which bore a close resemblance to 

 that of the red prussiate of potash. 



Since the invention of the chlor-hydrogen photometer 

 I have been able to observe more closely the habitudes 

 of chlorine. In the description given of that instrument 

 it is recommended to cast aside the first observation, be- 

 cause it never gives an accurate estimate of the true 

 effect. When a mixture of chlorine and hydrogen is 

 exposed, hydrochloric acid does not immediately form ; 

 but a preliminary absorption is necessary, and then at the 

 end of a certain period contraction begins to take place. 



Such a photometer exposed to the daylight is much 

 too powerfully affected to allow the successive stages 

 of change to be distinctly made out; the preliminary 

 modification is accomplished so rapidly that the indica- 

 tions 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 

 hydrogen, and marked the number of seconds which 

 elapsed before contraction, arising from the production 

 of hydrochloric 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 



third 



fourth 



fifth 



sixth 



105 



130 



95 



93 



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 

 combination takes place, and that in the case of chlorine 

 and hydrogen the total action is divisible into two 



