Ozone and Ozone Tests. 165 



below which the powder was slightly yellow ; Hydrochloric 

 Acid, grey pink, on tlie surface only, the powder beneath orange; 

 Nitric Acid, dark red-brown, extending slightly into the powder, 

 beneath colourless ; Carbonate of Iron with Glacial Acetic 

 Acid, yellowish-brown, penetrating to the thickness of card- 

 board, below which buff; Limestone with Sulphuric Acid, pale- 

 brown to the thickness of cardboard, beneath which slightly 

 coloured ; Carbonate op Iron with Sulphuric Acid, black to the 

 depth of a quarter of an inch ; Nitrous Acid, dark brown more 

 than an eighth of an inch deep, beneath which yellowish-brown. 

 These differences are so striking that important results must 

 follow their investigation. 



The action of ozone on the powders is somewhat analogous 

 to that produced by nitric acid ; yet dilute nitric acid, when 

 increased to ten times the strength which the French philoso- 

 phers declare is the proportion present in the air, is far too 

 weak to produce any colour on the tests. 



There are marked advantages in the powder tests over the 

 ordinary test-slips ; they are more sensitive and more rapidly 

 acted upon, and they retain their maximum colour, not fading 

 afterwards, as is the case with the test-slips of Schonbein and 

 Moffat. For one of Mr. Grlaisher's scientific balloon ascents I 

 prepared some doubly- sensitive powder tests, which showed the 

 presence of ozone in the short space of four minutes after 

 leaving the earth, whilst the test-slips remained for nearly an 

 hour uncoloured. 



A careful consideration of several thousand experiments 

 inclines me to the belief that ozone is always present in the air, 

 as on no occasion has my sensitive dry powder test failed to 

 show traces of it, even at a time when the ordinary test-slips 

 have remained for days uncoloured. 



Mr. Burder, of Clifton, near Bristol, has drawn attention to 

 the fact that ozone is never present in a room even with the 

 window open. Last autumn I carried on a series of experi- 

 ments, from which the same fact was arrived at, so far as 

 regards the ordinary test-slips, and this is because the air is 

 more or less stagnant in doors; were these test-slips to be 

 exposed out of doors whilst the air was calm or stagnant, they 

 would not exhibit any signs of ozone. However, my delicate 

 powder tests became faintly coloured not only with the 

 window open, but in an apartment with a closed window. The 

 current produced by a fire conveyed sufficient ozonized air 

 across the test-powder to show the presence of a small quantity 

 of ozone. 



On the completion of a second series of experiments, we 

 will return to the subject. 



