CHAPTER V. 



EFFECTS OF THE ELECTRICAL CURRENT. 



Thermal effects. A sufficiently strong electric 

 current is capable of fusing all metals, not excepting 

 platinum. By properly graduating the strength of 

 the current, varying degrees of thermal effects may 

 be obtained, from mere warmth up to redness, and on 

 to fusion. Heating effects, whether easily apparent 

 or not, always attend "the conduction of a current. 

 The amount of heating depends on the resistance of 

 the conductor. Thus, a fine wire will be heated to 

 a greater extent than a thick wire, and a wire of 

 great resistance to a greater extent than one of small 

 resistance. Thus, platinum wire interposes ten times 

 greater resistance to the passage of a current than a 

 copper wire of the same length and thickness. Con- 

 sequently, with the same current a platinum wire 

 would be unbearably hot, while a copper wire would 

 be hardly affected. At the same time, it is found 

 that the total resistance for the whole of the circuit 

 must be as small as possible. Therefore, when it is 

 desired to heat, say a small piece of platinum wire, as, 

 for instance, in surgery, for the removal by cautery of 

 a tumour, copper electrodes of considerable thickness 

 are attached to the battery, and the necessary length 

 of platinum wire is interposed between their ends. 

 (See chap, xi.) The heating effects of the currents 

 are made use of for firing mines, and for similar 

 purposes. 



Electrolysis. A current of electricity passed 

 through water decomposes it into its elements. Oxygen 



