1 86 GENERAL SCIENCE 



object employed as the cathode. Extra thick deposits 

 would constitute " double-plate " or " quadruple-plate." 

 In a similar manner nickel plating uses a solution of a com- 

 pound of nickel for the electrolyte, and copper plating uses 

 a solution of a copper compound. 



In Electricity as in other science subjects, theory aids in an 

 understanding of phenomena. By use of theories students 

 can comprehend in a few lessons the significance of phenom- 

 ena whose explanation is the result of years of patient re- 

 search on the part of many scientists. It is to be remembered , 

 too, that the accepted theories of science rest upon an 

 experimental basis, and seem to be verified in all cases where 

 they are applicable. At the same time they must never be 

 considered as statements of what is known to be true beyond 

 question. 



To aid in an understanding of electrolysis what is stated on 

 page 181 under Acids, Bases, and Salts is conceived to be 

 true. When some substances are dissolved, not only are 

 their molecules separated and scattered throughout the 

 solvent, but the molecules themselves break up into two parts 

 each known as ions. These parts may consist of single atoms 

 or of groups of atoms, and the more dilute the solution the 

 larger the extent to which this dissociation is carried. In 

 the case of sulphuric acid, the groups are considered as H 2 

 and S04. These electrified atoms or groups of atoms act 

 as carriers of electricity and serve to complete the circuit of 

 the current used in electrolysis. 



In the case of solutions of compounds of metals the metallic 

 ions pass from the solution to the cathode where they give 

 up their charge of electricity, and as atoms free of electrifica- 

 tion they collect on the cathode as pure metal. It is found 

 that if the anode in such cases consists of the same kind of 

 metal as that which is being deposited, or of any impure 

 form of it, this anode wastes as result of the electrolytic 



