Solutions of Iodides under the Influence of Actinism. 95 



On comparison of the arithmetical means of the results ob- 

 tained in fifty- four trials during the course of the same day, 

 the striking fact is brought out that the amounts of iodine 

 liberated by the two acids in the presence of the same base 

 stand in a constant ratio to one another. The law of actinic 

 force herein indicated may provisionally be expressed by the 

 formula — The chemism of the chlorine radical is to that of the 

 ■JS0 4 radical (measured by the relative amounts of iodine 

 liberated by each respectively in solutions of the metallic 

 iodides exposed to the sunlight) as 1-47 : 1. There is no 

 reason for inferring from the experiments that a similar defi- 

 nite ratio exists between the amounts of iodine liberated from 

 different soluble iodides in the presence of the same acid. 



Comparison of the Actinic Intensities of the Solar, Electric, 

 and Magnesium Light. 



In making this comparison, the amounts of iodine liberated 

 at the hoar of maximum actinic intensity (1-1.30 p.m.) were 

 taken in the case of the sun. The electric light was that 

 emanating from a lamp of 7000 candle-power falling upon the 

 solutions at a distance of six inches ; the magnesium light, 

 that derived from the burning of a single ribbon in the ordi- 

 nary lamp placed at the same distance. The time of expo- 

 sure to the electric light was 10 minutes, to the magnesium 

 light 25 minutes, to the sun ^ an hour ; in the table all are 

 calculated to one hour. 



Solar. Electric. Magnesium. 



H 2 S0 4 + KI . . 



HC1 + „ . . 



H 2 S0 4 + CdI 2 . 



HC1 + „ . . 



H 2 S0 4 + LiI . . 



flCl + „ . . 



On examining this table, and still more readily the graphical 

 illustration accompanying it, two phenomena become forcibly 

 manifest: — 



1st. The very much greater actinic intensity of the electric 

 as compared with the solar ray, when compared in the manner 

 indicated, and the very much less intensity of the magnesium. 

 In order to bring the magnesium curve into the same diagram 

 as the others, the numbers in the magnesium column were all 

 multiplied by 10. 



2-70 



10-0 



0-084 



4-00 



24-0 



0-87 



2-04 



9-5 



0-072 



3-00 



24-0 



0-6 



1-44 



5-0 



none 



2-40 



15-0 



0-3 



