1 78 ELEMENTARY LESSONS ON [CHAP. in. 



The weight of each measured cubic centimetre of hydro- 

 gen (at the standard temperature of o C, and pressure 

 of 760 millims.) is known to be -0000896 grammes. 

 Hence, if the number of cubic centimetres liberated 

 during a given time by a current of unknown strength 

 be ascertained, the strength of the current can be calcu- 

 lated by first reducing the volume to weight, and then 

 dividing by the electro chemical equivalent, and by the 

 time. Each weber of electricity liberates in its flow 

 1176 cubic centimetres of hydrogen, and -0588 c. c. 

 of oxygen. If these gases are collected together in a 

 mixed-gas voltameter there will be -1664 c. c. of the 

 mixed gases evolved for every weber of electricity which 

 passes. To decompose 9 grammes of water, liberating 

 i gramme of H and 8 grammes of O, requires 95,050 

 webers. 



216. Copper Voltameter. As mentioned above, 

 if sulphate of copper is electrolysed between two electrodes 

 of copper, the anode is slowly dissolved, and the kathode 

 receives an equal quantity of copper as a deposit on its 

 surface. By weighing one of the electrodes before and 

 after the passage of a current, the gain (or loss) will be 

 proportional to the quantity of electricity that has passed. 1 

 One weber of electricity will cause -0003307 grammes 

 to be deposited ; and to deposit one gramme weight 

 requires a total quantity of 3024 webers to flow through 

 the electrodes. 



217. Comparison of Voltameters with Gal- 

 vanometers. It will be seen that both Galvanometers 

 and Voltameters are intended to measure the strength of 

 currents, one by magnetic, the other by chemical means. 

 Faraday demonstrated that the magnetic and the chemical 

 actions of a current are proportional to one another. 



1 In 1879 Edison, the inventor, proposed to apply this method for measur- 

 ing the quantity of electricity supplied to houses for electric lights in them ; 

 a small copper Voltameter being placed in a branch of the circuit which 

 supplied the house, to sei ve as a meter. 



