102 PROCEEDINGS OF THE AMERICAN ACADEMY 



means of measuring the amount of chemical change caused by sohir 

 radiation. 



We have also stated, that, even in the dark, iodide of antimony is 

 oxidized by ozone. The experiment is easily made by passing through 

 the disulphide of carbon solution a current of air which has been 

 ozonized by electricity. The action is very marked, but not so rapid 

 as in the direct sunlight. The products are the same in both cases, — 

 oxi-iodide of antimony and free iodine ; and, under the influence of the 

 sun's direct rays, all the iodide of antimony can be thus, with time, 

 removed from the solution. 



The reaction we are considering was first observed in a closed flask, 

 and the circumstances wex'e such that we did not at first suspect the 

 important part which the atmospheric air played in the process. This 

 however, became evident as soon as we had examined the products of 

 the reaction ; and we then made experiments to determine whether any 

 reaction would take place out of contact with the air. For this pur- 

 pose, we sealed up the solution in flasks from which the air had been 

 displaced by carbonic dioxide, and, under these conditions, exposed the 

 solution to the direct sun's light. But, although it was easy in this 

 way to preclude any considerable change, we did not succeed in pre- 

 venting it altogether. A slight reddening and turbidity indicated at 

 least the beginning of oxidation, and this we traced to the oxygen gas 

 held in solution by carbonic disulphide. But, after this small amount 

 was exhausted, the action was wholly arrested, though we exposed the 

 solution for days to the briglitest sunlight. 



Carbonic disulphide obviously aids the reaction by dissolving oxygen 

 gas, as well as antimonious iodide ; but we must not overlook what we 

 stated in the previous paper, — that the same oxidation may take place 

 independently of this solvent. The crystals of antimonious iodide, the 

 yellow as well as the red, soon become coated with oxi-iodide, when 

 exposed to the light and air ; and we have lost a number of fine speci- 

 mens from this cause. Under the microscope, the oxi-iodide appears 

 as a yellow efflorescence, which soon destroys the transparency of the 

 mass ; and the odor of free iodine can be perceived on opening the 

 bottle in which the preparation has been kept. This action, of course, 

 is comparatively slow, but not less definite than that which we have 

 been previously considering. 



The oxi-iodide which, during oxidation, falls from the solution of 

 antimonious iodide, is an amorphous yellow or brownish yellow pow- 

 der. As it is insoluble in carbonic disulphide, it can easily be sepa- 

 rated and cleaned by filtration and washing with this liquid. We made 

 analyses of three different preparations, with the following results: — 



