252 SCIENCE FROM AN EASY CHAIR 



owing to the liberation of iodine and the formation of its 

 well-known blue combination with the starch. Schonbein 

 found that in breezy, fresh places his test-papers turned 

 blue, and concluded from that (confirmed by other evidence) 

 that this smelling gas, to which he gave the name ozone 

 which simply means "the smelling stuff" is present in 

 good, ordinary atmospheric air, as well as in artificially 

 "electrified" air. It is destroyed when such air is heated 

 above the boiling-point of water, and seems to be, as it 

 were, " taken out " of the air by all sorts of dead organic 

 matter, so that it is not present in the air of large cities. 

 I remember that when I was a boy we used to test the 

 air for ozone with Schonbein's papers (I am aware that 

 their colour change is not absolute proof of the presence 

 of ozone, as other oxydising gases might, if present, act in 

 the same way), and we used to find more ozone when a 

 south-west wind was blowing than in a north-easter ! 



Schonbein wrote sixty papers on ozone but its real 

 nature was made out by others who succeeded him, 

 chiefly by Andrews, of Belfast, and Tait, of Edinburgh. 

 It turns out that ozone is a condensed form of the 

 elemental gas oxygen squeezed, as it were, and literally 

 " intensified," so that three measures of oxygen gas become 

 only two of ozone. It very readily changes back again 

 two measures of ozone expanding to form three of oxygen. 

 It is produced by the action of an electric discharge upon 

 oxygen gas driven over the discharge and in greatest 

 quantity when that kind of gently-buzzing electric spark 

 which is called "the silent discharge" is used. It can be 

 produced in quantity by passing atmospheric air, or better, 

 pure dry oxygen gas through a glass tube in which such a 

 silent discharge is made to take place. As much as seven- 

 teen parts in a hundred of the gas can be thus converted 

 into "ozone," and some twenty years ago two French 

 chemists succeeded in getting even a larger proportion, 



