A. W. Wright—Electrical Deposition of Metals. 171 
from which the electrode projected, the latter being adjusted to 
the proper distance by sliding it up or down in its support as 
the plate. In some of the experiments the plate was station- 
ary, being held in a little tripod of glass threads, or simply laid 
upon the bottom of the globe. In these cases the tube hold- 
ing the electrode was jointed near the top, the two portions 
being connected by a hook and loop of platinum or magne- 
sium wire. It could thus be made to traverse all parts of the 
plate by giving suitable movements to the globe. 
hen adjusted and closed the receiver was attached to the 
Sprengel pump. By means of a small air-pump of the ordi- 
nary construction, connected with this by a stop-cock and flex- 
ible tube, the whole apparatus was exhausted as far as possible 
and then dry hydrogen admitted, this being repeated two or 
three times in order to remove the air and moisture. ‘The pro- 
cess of exhaustion was then completed with the mercury pump. 
The degree of rarefaction required varied somewhat with the 
metal to be deposited, but was rarely above 2°5 millimeters. 
For platinum the best results were obtained, when it was from 
15 to 1-75 millimeters. The use of hydrogen is not in all cases 
necessary, as some of the metals can be deposited perfectly 
well with only air in the receiver. This is especially the case 
with gold, but platinum, although ordinarily not easily com- 
bined with oxygen, becomes tarnished with a film of what 
apparently is A blue oxide, unless the air is removed. The 
electrode itself was formed of a small wire, usually not more 
than one-fourth of a millimeter in thickness, bent at the end 
ree to six in 
rather weak acid, and a plunge ba f fiv 
two, or more were PE as Oc uired, the whole being 
