Mr. Williamson on Ozone. 375 



oxygen and that produced by the action of phosphorus on 

 atmospheric air. To what then is to be attributed the reaction 

 produced by the direct action of air passed over phosphorus 

 on iodide of potassium and starch ? The following experi- 

 ment was made. In a long and wide tube loose pieces of 

 asbestos and pieces of phosphorus were placed alternately. 

 By heating the tube thus filled the phosphorus was partly 

 melted into the asbestos, and partly sublimed upon it; thus 

 exposing a far greater surface than in the former experiments. 



After the tube had completely cooled, atmospheric air was 

 driven through it into the iodide and starch, but not the 

 slightest reaction was produced. 



This result plainly indicates the cause of the reaction in the 

 preceding instance. The phosphorus was there unable for 

 want of sufficient surface to absorb all the oxygen of the air 

 passing over it. A mixture of phosphoric acid and oxygen 

 therefore went over, and by their simultaneous action on the 

 iodide of potassium set iodine free. As soon as a sufficient 

 surface was given to the phosphorus all oxygen was absorbed, 

 phosphoric acid was alone carried over by the nitrogen, and 

 the iodide was decomposed in a different manner. 



Lime water, through which the air thus treated with phos- 

 phorus was passed, deposited a voluminous sediment, consist- 

 ing of phosphate of lime. This liquid cleared by a few drops 

 of acid remained afterwards unclouded on being heated with 

 chloride of mercury : it consequently contained no phospho- 

 rous acid. With iodide and starch it gave no reaction, either 

 alone, or after an acid was added to it. 



These experiments appear to me to show, — 



I. That the peculiar properties belonging to the oxygen 

 set free by the agency of the electric current are produced by 

 the admixture o^ a. peroxide or acid of' hydrogen ; 



II. That by the action of phosphorus on atmospheric air 

 the same substance is not pr-oduced. 



That this compound of hydrogen and oxygen is not identical 

 with Thenard's peroxide, would appear from the fact of its 

 being volatile and odorous, properties which the other does 

 not possess. I have repeatedly prepared Thenard's peroxide 

 of hydrogen by decomposing peroxide of barium with different 

 acids, for the purpose of satisfying myself whether it ever 

 possesses odour, but have always obtained a negative result. 

 The oxygen disengaged from it by the action of peroxide of 

 manganese is as inodorous as the liquid itself. The oxygen 

 obtained by the electrolytical decomposition of an aqueous 

 solution of peroxide of hydrogen possesses the same odour, 

 only apparently in a somewhat greater degree, as that from 

 water. 



