398 Dr. A. K. Leeds on the Action of Light 



Electric Li 



ght. 







20 minutes. 



7^ minutes. 



1 c.c. H 2 S0 4 + 1 c.c. KI = 3-90 mgrms. I. 



= 3*00 mgrms. I 



„ HCl „ =3-15 



?j 



= 2-00 



?> 



« » » = 3 ' 40 



V 



— 





1 c.c. H 2 S0 4 + 1 c.c. Cdl 2 = 3-15 



V 



= 2-25 



?? 



„ HCl „ =2-30 



?} 



= 1-35 



J? 



„ „ „ =2*50 



V 



— 





lc.c.H 2 S0 4 + lc.c.LiI =3-00 



?3 



= 2-10 



V 



„ HCl „ =1-70 



JJ 



= 1-00 



)) 



1 c.c. H 2 S0 4 + 1 c.c. NH 4 1=2*50 



H 



= 2-30 



V 



„ HCl „ =1-50 



JJ 



= 1-50 



J? 



„ HCl „ =1-85 



J? 



— 





The reason for the variation in the two experiments is not 

 quite clear ; for while the light was remarkably uniform du- 

 ring the second experiment, there was no such striking differ- 

 ence in the apparent luminous effect. 



Magnesium Light. 



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



„ HCl 



„ H 2 S0 4 + Ic.c.CdI 2 



„ HCl „ 



„ H 2 S0 4 + lc.c.LiI 



„ HCl „ 



„ H 2 S0 4 +lc.c.NH 4 ] 



„ HCl „ 



The light was furnished by a single-ribbon magnesium 

 lamp, run by clockwork. The reason for repeating the expe- 

 riment three times was that the ratio of decomposition in pre- 

 sence of free hydrochloric acid was greater than in presence 

 of free sulphuric acid. When the sun and electric light were 

 employed, it was always less, the reagents being of the 

 strengths above given. It will be necessary to determine the 

 rate of decomposition in each case, for the various regions of 

 the spectra of the three lights, before venturing upon an ex- 

 planation of these differences. 



The foregoing results are brought together in the following 

 Table, and likewise illustrated in the diagram. The numbers 

 found for the magnesium light have been multiplied by ten, 

 in order to bring the corresponding curve into the same illus- 

 tration with the others. 



I. 



II. (1 hour). 



III. (| hour) 



mgrm. I. 



mgrm. I. 



mgrm. I. 



lost 



= 0-050 



= 0-015 



= 0-225 



= 0-075 



= 0-050 



= 0*080 



= 0-035 



= 0-010 



= 0-150 



= 0-050 



= 0-050 



= 0-075 



= 0-040 



indet. 



= 0*165 



= 0-050 



= 0-060 



= 0-115 



= 0-060 



— 



= 0-200 



= 0-070 



— 



