by the electrical discharge in exhausted tubes. 51 



For metals readily oxidized it was necessary to fill the tubes 

 with some gas which would not act upon the deposit formed, as 

 otherwise it was impossible to obtain good results. In these 

 cases the air was first thoroughly removed, the tube filled with 

 pure dry hydrogen, and then exhausted. In a few cases the 

 tubes were refilled with hydrogen several times to ensure the 

 complete removal of the oxygen. The perfection of the film 

 was found to depend also in some measure upon the steads ess 

 of the electrical action, and the proper regulation of the power 

 of the current used. When the Holtz machine was employed 

 as a source of electricity no effect was obtained without con- 

 densers, and with them the discharge, at least with the tension 

 of gas used, did not occur in such a manner as to yield good 

 results. The trifling deposit obtained in this way was opposite 

 the positive electrode. Possibly by exhausting the tubes so as 

 to reach a much lower tension tile electro-machine might be 

 made available, but the induction coil is both eificient and con- 



With a gold wire one-third of a millimeter in diameter and 

 four centimeters long, an exquisitely beautiful deposit was 

 formed over a space a little longer than the wire. The first 

 noticeable effect was a slight discoloration of the tube by the 

 deposited metal, while it was still too thin to show the metallic 

 luster by reflected light The tint was pinkish, inclining to 

 violet, resembling that at the more refrangible end of the spec- 

 trum. As the film increased, the tint passed through blue, 

 bluish-green, and finally, when of sufficient thickness, it ap- 

 peared a clear, brilliant green, slightly inclining to bluish- 

 green. Bv reflected light the film has a splendid luster, and 



l 'Men color. It thins out gradually at the M ' 

 and becomes imperceptible at a point five or six millimeters 

 from the end of the wire, with the same gradation of tints as 

 was ol .served in its formation. The metallic reflection fades 

 out in a similar manner, but ceases before the coloration. 



With -: ; iie same dimensions, the coating 



upon the tube was sea, and perfect. The full 



1 wd r was developed gradually, and the light transmitted by the 

 completed film is a pure, deep blue. Copper gives a^fine lus- 

 trous mirror, appearing dull gre<: ^- " » 

 vol ti „vd with more difficulty than the preceding metals. 

 Bismuth on the other hand is obtained in a thin film with ex- 

 treme ease, a battery of three small Grove cells with a coil 

 giving a half inch spark producing the desired result in two or 

 three minute* The film is very transparent, and has a color 

 such as would be produced by mixing a clear blue with a pure 

 grav or neutral tint. The metallic layer is remarkably uniform 

 and of great beauty, possessing a brilliant luster by reflected 

 light. 



