SEA-BREEZES, MOUNTAIN AIR, AND OZONE 253 



and by submitting it to a tremendous pressure at a 

 temperature of 100 degrees below the freezing-point of 

 water, they obtained pure ozone as a transparent liquid. 

 It was of a dark indigo-blue colour, and somewhat danger- 

 ous and explosive when the pressure under which it had 

 formed was removed. Ordinary oxygen gas has since 

 then been also liquefied in the laboratory : it is of a paler 

 blue colour. 



The "smell" which old writers had noticed and 

 Schonbein had named was thus actually obtained as a 

 distinct blue liquid. It is this which, though present only 

 in minute quantities, gives special oxydising activity to 

 fresh air. When pure, or present even to the small 

 extent of 4 per cent, in air, ozone is a destructive agent, a 

 sort of extra-quality oxygen of triple instead of double 

 power. Indiarubber is rotted and destroyed by it in a few 

 minutes a sort of combustion or quick oxydation taking 

 place and it is, of course, dangerous to the softer parts 

 of the human body, such as the air passages and lungs 

 and the eyes when present in more than a minimal 

 proportion. I believe that no one has yet determined 

 exactly how great a percentage of ozone can be tolerated 

 by a human being in the air taken into the lungs. In 

 ordinary fresh country or sea-coast air only one part by 

 measure in 700,000 has been found to be ozone, that 

 is, TT^ per cent. But it is quite likely that much more 

 is occasionally present, since it is very difficult to arrange 

 a satisfactory examination of the air of any locality so as 

 to determine how much ozone it contains. It is said that 

 at higher levels the atmosphere contains more ozone than 

 it does at lower levels. 



It is not to be wondered at that ozone should thus 

 have attracted general attention and interest as the dis- 

 tinctive and specially active agent present in the pure 

 air of the sea- coast and the mountain-top. People not 



