1886.] 



Experiments on the Production of Ozone. 



341 



phosphorous pentoxide, pumice moistened with sulphuric acid, and 

 caustic potash ; it was also freed from dust by passing through a 

 tube containing a plug of cotton-wool. After passing through the 

 box it bubbled through a test-tube, F, containing an iodide of 

 potassium and starch solution, pieces of filter-paper moistened with 

 this solution were also fastened to the sides of the box. We deter- 

 mined the most sensitive solution of potassium iodide and starch by 

 adding a constant quantity of chlorine-water to various proportions 

 of potassium iodide and starch ; when the most sensitive solution had 

 been determined it was always made up of this strength. We found 

 that the papers were quite as delicate a test of ozone as the test-tube 

 full of the solution. 



When the observations were being made the whole arrangement 

 was placed inside a large wooden box, the sides of which were 

 blackened, the observer put his head through a hole in one of the 



