172 THE DECOMPOSITION OF CAEBONIC-ACID GAS. [MEMOIR X. 



Fig. 21 represents one of these closets; a a is its side 



of stained - glass, or the 

 trough containing the ab- 

 sorbing solution, bichro- 

 mate of potash, etc. ; b b, 

 the door. 



Whenever an experi- 

 ment was commenced in 

 these closets, a similar one 

 Ir ~n^ r was simultaneously com- 



menced in the unobstruct- 

 ed sunshine. It is needless to state that in all these 

 care was taken to have the different arrangements for 

 decomposition as nearly alike as possible. 



On comparing the amount of gas evolved in unab- 

 sorbed light and in light that had undergone absorption 

 by bichromate of potash, in three out of five trials the 

 gas collected under the latter circumstances exceeded in 

 volume that collected under the former; this was prob- 

 ably due to a higher temperature existing in the box. 



On comparing the volume of gas collected under bi- 

 chromate of potash and under litmus -water, the latter 

 was not equal to half the former. 



I compared the gas evolved in unobstructed light, 

 under bichromate of potash, and under ammonia sul- 

 phate of copper; the results were as follows: 



Unobstructed light 4.75 



Bichromate of potash 4.25 



Ammonia sulphate of copper 75 



It therefore appears that light which has passed 

 through bichromate of potash, by which the chemical 

 rays have been absorbed, can accomplish this decompo- 

 sition ; but light which has passed through ammonia 

 sulphate of copper, which transmits the chemical rays, 

 fails to produce that effect. 



