44 ELECTRICITY. 



(58) THE HEATING EFFECTS OF CUUHENTS. 



According to Joule's law : the number of calories (gram-degrees) 

 of heat developed in a circuit is equal to the square of the current 

 multiplied by the time and by the resistance of the circuit, and 

 divided by the mechanical equivalent of the unit of heat, all in 

 C.G.S. units. 



T2f)f 



H = ~ (where J = 4 '2 X 10 7 ergs). 

 J 



But if / be expressed in amperes and R in ohms, this value 

 must be multiplied by 10 - 2 X 10 9 or 10 7 . 



Hence a current of one ampere in working through one volt 

 develops in the circuit an amount of energy called a JOULE, the 

 heating effect of which is equivalent to 0'2406 calorie. 



It is frequently convenient to express the rate at which a current 

 of one ampere when acting through one volt does work by means 

 of the ' * WATT. " 



A WATT then is the rate at which work is done by a current 

 of one ampere working through one volt ; it is equivalent to 10 

 meg-ergs or T^tr (= '00134) horse power or '7373 foot-pound per 

 second ; or to 7^ (= *00136) of a cheval-vapeur or '100 kilogram- 

 metre per second. 



(59) ELECTROLYSIS. (Cf. 80.) 



The amount of a radicle (ion) liberated by a current is proportional 

 to the strength of the current ; and the mass of it in grams is equal 

 to the product of the strength of the current in amperes, its 

 duration in seconds, the chemical equivalent of the radicle set free, 

 and lastly, of the mass of hydrogen set free by one coulomb of 

 electricity. 



According to F. Kohlrausch a coulomb of electricity sets free 



0011363 gm. of silver, which is equivalent to ,-, 



107 'oo 

 0-00001055 gm. of hydrogen. 



Mascart finds that a coulomb of electricity sets free '000010415 

 gm. of hydrogen. 



According to Gray a coulomb of electricity deposits '000331 gm. 



AAAQQi 



of copper, which is equivalent to - - = '000010478 gm. 



dl '59 

 cf hydrogen. 



Hence 1 coulomb of electricity sets free very nearly '0000105 gm. 

 of hydrogen; '0000105 X 108, or '001134 gm. diver; '0000105 



X v or '000084 gm. oxygen ; '0000105 X rr, or '0005145 gm. 



< *4 



hydrogen sulphate. 



