149 



X. On the Properties of Voltaic Circles, in which concentrated Sulphuric 

 Acid is the Liquid Conductor. By Thomas Andrews, M.D., Professor 

 of Chemistry in the Royal Belfast Institution. 



Read 9th April, 1838. 



The remarkable discovery of Professor Schoenbein of Bale respecting the 

 modification which the chemical action of nitric acid upon iron undergoes when 

 they are brought into contact under certain voltaic conditions, has led me to 

 examine the general phenomena which are exhibited by voltaic circles whose 

 liquid conductor consists of a concentrated acid. In a paper read at the last 

 meeting of the British Association, I showed that the solution of the oxidable 

 metals in strong nitric acid is greatly retarded when they are voltaically asso- 

 ciated with such metals as platina, upon which that acid has no action ; a result 

 which is evidently the reverse of the ordinary effect of the passage of an elec- 

 trical current. The object of the present communication is to extend the same 

 principle to the action of concentrated sulphuric acid under similar conditions, 

 and to investigate some of the circumstances which influence the development of 

 electrical currents in this way. 



When a piece of zinc is introduced into strong sulphuric acid (sp. gr. 1.847) 

 at common temperatures, its surface becomes covered with a mass of gaseous 

 bubbles, so fine that they might be almost mistaken for a white precipitate, which 

 very slowly separate from the zinc, but by agitation, or the application of a gentle 

 heat, may be easily removed. The gas thus disengaged is hydrogen in a state 

 of perfect purity. On applying heat to the acid there is scarcely any further 

 extrication of gas, till the temperature has reached nearly 100° cent., when a 

 very fine stream of gas begins to arise from the surface of the zinc. As the heat 

 is raised, the quantity of gas becomes more considerable ; from 120° to 150° cent, 

 there is a rapid effervescence, and at still higher temperatures vast quantities of 



