Jo Sep J I Baxendell^ F.R.S. 53 



to the air has the power of condensing oxygen upon its 

 surface into a thin film of ozone ; when, therefore, complete 

 evaporation of the vesicles or globules of moisture which 

 constitute a cloud or fog takes place, the ozone is left free 

 to diffuse itself through the air, but when evaporation takes 

 place from the surface of a large and practically inexhaustible 

 mass of water the ozone is not set free, but remains adhering 

 to the surface. To meet the objection that if ozone is formed 

 in this way, test papers ought to be coloured very rapidly 

 in a fog or dense haze, and that no bleaching action could 

 take place upon papers already ozonised, he ventures to 

 offer as an explanation, that ozone associated with moisture 

 and in the presence of the oxidised potassiums, will combine 

 with the freed iodine and form iodic acid, which, uniting 

 with the potash, will form the colourless iodate of potash ; 

 or it may be that the direct action of ozone on iodide of 

 potassium is retarded, or altogether prevented, by an excess 

 of moisture when the ozone is present in only small quanti- 

 ties, as is usually the case in the atmosphere. That ozone 

 should oxidise the free iodine as Mr. Baxendell suggests to 

 iodic acid seems improbable. The following explanation 

 seems possible: if ozone decompose iodide of potassium into 

 iodine and free alkali, should the paper become slightly 

 damp, the reverse action would take place, and the 

 iodine would be converted into iodide and iodate of 

 potassium. A member of this Society, to whom Mr. 

 Baxendell had often mentioned the bleaching of the 

 papers, stated that he thought he could distinguish 

 those which had been bleached from those which had not 

 been exposed. As a challenge Mr. Baxendell sent four 

 numbered papers which were quite similar in appearance, 

 but revealed a difference when tested ; two were stated to 

 have been exposed, and two to be fresh papers. Mr. 

 Baxendell wrote in reply that they were rightly grouped. 

 The method of discrimination was extremely simple, and 



