Solutions of Iodides under the Influence of Actinism. 93 



metric use of nitric acid was discontinued until the exact influ- 

 ence of temperature, actinism, oxygen, and organic matter 

 upon its special rate of change had been established, and the 

 nature of the accompanying reactions'*. 



In order to study the influence of mineral acids, trials were 

 made as above, the solutions being of such strength that 1 c.c. of 

 each was chemically equivalent to the same amount of mineral 

 acid. 



Effect of Organic Acids. March 20. 10.10 A.M. to 1.10 P.M. 

 Good Sunlight. 



Oxalic acid + potassium iodide = 6*5 mgrms. I. 

 „ + cadmium „ =6'0 „ 



„ 4- lithium „ =5*75 „ 



Tartaric acid + potassium „ =0*10 mgrm. I. 

 „ + cadmium „ =0*00 „ 



„ + lithium „ =0-00 „ 



Nor any change with acetic acid during this three-hour 

 interval. To determine more precisely the rate of change 

 effected by the organic as compared with the mineral acids, it 

 will be necessary to make simultaneous estimations; but even 

 with oxalic acid, the most active of them all, it is evident that 

 the amount of decomposition was relatively small. 



An actinometric measurement of the solar ray was made 

 with the equivalent solutions of various iodides and acids — the 

 principal object being to note the effect upon the rate of de- 

 composition of different acids in the presence of the same base, 

 and of different basic radicals of the iodides in the presence of 

 the same acid. The sunlight, which was good during the 

 early part of the day, declined towards noon ; and shortly 

 afterwards the sky became overcast. 



Actinometric Measurement of the Solar Rag. March 26, 1879. 





9.30-1 10- 



10.30 



11- 



11.30 



12- 12.30 



1- 



Means. 



Eatios. 





10 A.M.10.30. 



-11. 



11.30. 



-12. 



12.30.1 -1. 



1.30. 



H. 2 S0 4 +KI... 

 HC1 +KI... 



1-55 



1-81 



21 



206 



1-87 



1-7 



1-6 



075 



1-68 



BLS0 4 :HCL 



2-4 



26 



2-75 



2-66 



2-39 



2-15 



2-05 



2-0 



2-5 



1:1-48 



H 2 S0 4 + CdL. 



1-5 



1-62 



1-81 



1-81 



1-56 



1-29 



1-19 



118 



1-49 



H 2 S0 4 : HC1. 



HC1 4-CdI . 



2-4 



2-35 



263 



2-68 



209 



1-79 



1-79 



1-75 



2-18 



1 : 1-46 



H 2 S0 4 4-LiI.. 



118 



1-28 



1-41 



1-35 



1-13 



0-96 



0-93 



0-93 



115 



H 2 S0 4 :HC1. 



HOI +LiI.. 



1-83 



1-9 



203 



2-0 



1-56 



1-25 



1-58 



1-4 



1-69 



1 : 1-47 



* Gay-Lussac states {Ann. de Chim. et de Phtjs. 1816, p. 317) that no 

 decomposition of dilute acid takes place in the light, except in the pre- 

 sence of a certain quantity of concentrated sulphuric acid ; also that the 

 decomposition is into nitrous acid. 



