172 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1911. 
Refining of metals—Unless metals are of high purity they are 
usually of very little usefulness. Electrolytic methods enable almost 
perfect purity to be easily attained, and in addition permit the separa- 
tion at the same time of the valuable gold and silver contained in small 
amounts in the, baser metals. Over $100,000,000 worth of copper is 
electrically refined every year in the United States; the metal pro- 
duced is purer than can be otherwise obtained, giving the electrical 
engineer the highest grade of conducting metal, while several million 
dollars’ worth of gold and silver are recovered which would otherwise 
have to be allowed to remain in the copper. Again, the method is so 
simple that but a few words are necessary to set it forth in principle. 
The impure copper is used as one electrode—the anode—in a solution 
of copper sulphate containing some sulphuric acid; the receiving elec- 
trode—the cathode—is a thin sheet of pure copper, or of lead, greased. 
The electric action causes pure copper only to deposit upon the cath- 
ode, if a properly regulated current is used, while a corresponding 
amount of metal is dissolved from the anode. Silver, gold, and plati- 
num are undissolved, and remain as mud or sediment in the bottom 
of the bath; other impurities may go into the solution, but are not 
deposited on the cathode if the current is kept low. The cost of this 
operation is small, and the results are so highly satisfactory that 90 
per cent of all the copper produced is thus refined. Similar methods 
are in use for refining other metals, silver, gold, and lead are thus 
refined on a large scale; antimony, bismuth, tin, platinum, zinc, and 
even iron can be thus refined; the field is very inviting to the experi- 
menter and to the technologist, and is rapidly increasing in industrial 
importance. ° 
Metal plating.—A\i electroplating is done by the use of electrolytic 
methods similar to those just described. If we imagine the impure 
metal anode replaced by pure metal, and the receiving cathode to be 
the object to be electroplated, we have before us the electroplating 
bath ready for action. Everybody knows the value and use of gold, 
silver, and nickel plating; less well known are platinum, cadmium, 
chromium, zinc, brass, and bronze plating. These are among the 
oldest of the electrochemical industries. Electrotyping is only a 
variation of this work; also the electrolytic reproduction of medals, 
engravings, cuts, etc., and even the production of metallic articles of 
various and complicated forms, such as tubes, needles, mirrors, vases, 
statues, etc. The speaker has translated from the German a mono- 
graph concerning these last-named uses of the electric current. There 
is opportunity here to hardly more than catalogue these various 
branches of electrometallurgical activity. Pittsburgh people will be 
interested, however, in knowing that many of the newer buildings in 
this city contain thousands of feet of electrical conduits zine plated 
in splendid fashion by electrolysis, at a works within a few miles of 
