AND SCHONBEIN 51 



acid, as Faraday supposes. It is to the production 

 of ozone by the electricity that this action must be 

 ascribed. 4. The property of the electrical odour of 

 being destroyed by sulphurous acid, hydrogen sulphide 

 and hydrogen selenide. If in the neighbourhood of a 

 point from which electricity is being discharged the 

 merest trace of sulphurous acid is developed, as for 

 example by burning the sulphur of an ordinary match, 

 the peculiar smell which accompanies the discharge 

 of electricity into the air is perceived no longer. 

 Furthermore the electrical brush is no longer able 

 under these conditions to communicate negative 

 polarity to a gold or platinum strip held in it, or to 

 turn potassium iodide starch paste blue. Moreover 

 if such a strip is held only for a moment in a flask 

 containing some sulphurous acid, it will not be turned 

 blue when exposed to the action of the electric brush. 

 The action of hydrogen sulphide and selenide is 

 similar to that of sulphurous acid; the presence of 

 the smallest quantities of these substances in the 

 room containing the electrical machine is sufficient 

 to prevent the production of the electrical odour at 

 the point of the conductor and all the reactions de- 

 pending upon it. Now these substances destroy 

 chemically or voltaically prepared ozone in exactly 

 the same manner as the electrical odour. Hardly 

 any doubt can remain as to the identity of the ozone 

 prepared in the three ways described, and it may be 

 taken as incontestable that during the discharge of 

 electricity into the air a haloid substance similar to 

 chlorine is formed. Now since lightning is nothing 



