400 On the Action of Light upon the Soluble Iodides. 



Decomposition during equal times (1 hour). 



Electric light. Sun. Magnesium. 



H 2 S0 4 + KI = 19*5 mgrms. I. 6-5 mgrms. I. 0'05 mgr. I. 

 HC1 „ =13-0 „ 4-0 „ 0-075 , 



H 2 S0 4 + CdI 2 =14-6 „ 4-4 „ 0*035 , 



HC1 „ = 8-8 „ 3-0 „ 0-050 , 



H 2 S0 4 + LiI =13*7 „ 3-1 „ 0-04 , 



HC1 „ = 6-5 „ 2-4 „ 0-05 , 



H 2 S0 4 + NH 4 1 = 15-0 „ 3-9 „ 0-06 , 



HC1 „ = 9-8 „ 2-3 „ 0-07 , 



As yet no actinometric measurements of spectra have been 

 made by this method. As a preliminary determination, how- 

 ever, the amount of action upon the soluble iodides, after the 

 light of the sun and electric arc have traversed certain ab- 

 sorbing media, has been studied. The comparison-tubes were 

 supported in the centres of tall wide-mouth bottles, so as to be 

 surrounded by an equal thickness (3 centims.) of the absorb- 

 ing medium on every side. Their tops and those of the bottles 

 were closed in with tinfoil, so as entirely to prevent access of 

 light, but admit air. The blue medium was ammoniacal solu- 

 tion of copper ; the yellow, neutral potassium chromate ; the 

 red, fuchsine. Their strength was adjusted to the point of 

 equal translucency. 



Absorbing Media (time 1 hour). 



Blue. 



Yellow 



Ked. 



While in the preceding experiments the action in the elec- 

 tric light has been approximately the maximum of that occur- 

 ring in sunlight, this ratio, when absorbing media were used, 

 was approached only in case of the blue and red solutions. In 

 other words, the yellow medium absorbed a much larger rela- 

 tive proportion of the actinic rays of the electric light than of 

 those of the sun. 



Stevens Institute of Technology, 

 Hoboken, N.J., April 15, 1879. 





Sunlight. 



Electric light 





mgrms. I. 



mgrms. I. 



fl c.c. H 2 S0 4 + 1 c.o. KI 

 t „ HC1 



= 2-38 



= 6-00 



= 2-22 



= 4-50 



fl c.c. H 2 S0 4 +lc.c. KI 

 t „ HC1 



= 0-67 



= 0-50 



= 0-45 



= 0-45 



fl c.c. H 2 S0 4 +lc.c. KI 

 I „ HC1 



= 1-53 



= 4-95 



= 0-83 



= 3-00 



