i8o ELEMENTARY LESSONS ON [CHAP. in. 



Gymnotus. In fact, he relied on this chemical test as 

 one proof of the identity of the different kinds. 



219. Internal and External Actions. In an 

 earlier Lesson it was shown that the quantity of chemical 

 action inside the cells of the battery was proportional to 

 the strength of the current. Hence, Law (i.) of Art. 211, 

 applies both to the portion of the circuit within the 

 battery and to that without it. 



Suppose 3 Darnell's cells are being employed to decompose 

 water in a voltameter. Then while I gramme weight (11,200 

 cub. centims.) of hydrogen and 8 grammes (5,600 c. c.) of 

 oxygen are set free in the voltameter, 31*5 grammes of copper 

 will be deposited in each cell of the battery, and (neglecting loss 

 by local action), 32*5 grammes of zinc will be dissolved in each 

 cell. 



220. It will therefore be evident that the electrolytic 

 cell is the converse of the voltaic cell. The chemical work 

 done in the voltaic cell furnishes the energy of the current 

 which that cell sets up in the circuit. In the electrolytic 

 cell chemical work is performed, the necessary energy 

 being furnished by the current of electricity which is 

 sent into the cell from an independent battery or other 

 source. 



A theory of electrolysis, and some examples of its 

 application, are given in Chapter XXXVIII. on Electro- 

 chemistry. 



LESSON XIX. Physical and Physiological Effects of 

 the Current. 



221. Molecular Actions. Metal conductors, when 

 subjected to the prolonged action of currents, undergo 

 slow molecular changes. Wires of copper and brass 

 gradually become brittle under its influence. During 

 the passage of the current through metallic wires their 



