198 



Ozone and the Atmosphere. 



ing to the reaction which first attracted the attention of 

 Schonbein, that the following novel experiment, which affords 

 an impressive lecture illustration, is important. 



A glass tank is made, of 

 thin sides of plate glass, 

 and of less hight and breadth 

 than the diameter of a 

 magic lantern condenser. 

 These sides are held firmly 

 against rubber walls of 

 about 12 m. m. in thick- 

 ness, cut out in such man- 

 ner as to divide the tank 

 into two cells. One is part- 

 ly filled with acidulated water,* the other with a 15 p. c. so- 

 lution of potassium iodide. 



The platinum electrodes from a battery of six Bunsen cells, 

 rise from the bottom of the first compartment of the tank, 

 covered, except at their ends, with glass tubes into which the} r 

 have been previously sealed. A small bent glass delivery-tube 

 is slipped over the electro-positive pole, its end just dipping 

 beneath the surface of the potassium iodide solution. Decom- 

 position begins as soon as the mixture of ozygen and ozone has 

 displaced the air previously in the delivery-tube, and is made 

 evident by the yellow color imparted by the liberated iodine. 

 If, before projecting the image of the decomposition on the 

 screen, a few drops of dilute starch have been added, the dark 

 blue clouds, rolling away from the point of exit of the electro- 

 lytic ozone, are striking. A tincture of guaiacum, freshly 

 prepared from the solid resin, shows the presence of ozone by 

 a lighter blue coloration spreading across its surface in the 

 tank ; and an indigo solution is bleached. The last reaction is 

 not so striking as the foregoing, since the bleaching is necessa- 

 rily shown by a gradual, instead of an abrupt change of color. 

 This tank is a modification of that manufactured by Messrs. 



* According to L. Hoffman, a maximum liberation of ozone is obtained from a mixture of 

 1 part sulphuric acid and 5 parts water. (Pogg. 132, 607 ; Jahresb. der Chemie, 1867, 130). 

 Ike mixture eeould be kept as cold as possible. 



