1 of Transparent Metallic Films. 49 



.RT. VII.— Oh the produc 



lion of Tramparen 



I Metallic Films by 



the Electrical Discharge 



in exhausted tribes 



; by Arthur W. 



Wright, Professor of 



Molecular Physic 



s and Chemistry, 



Yale College. 







The spectra of gases contained in vacuum-tubes, which have 

 been prepared by the use of the mercury pump, usually exhibit 

 lines caused by the presence of the vapor or this metal. In 

 some cases this is no disadvantage, since they serve as conven- 

 ient reference points in fixing the position of the other lines or 

 bands observed. As the mercury vapor is naturally an excel- 

 lent conductor of electricity, however, there is often reason to 

 suspect that its presence may affect the character of the discharge 

 somewhat, and its removal becomes desirable. In some recent 

 experiments by the writer this end was obtained by placing in 

 each tube a lew pieces of clean gold foil loosely rolled into 

 small pellets. As this metal is readily amalgamated it will, 

 after a time, take up the mercury vapor, causing the disap- 

 pearance of its characteristic lines from the spectrum. A still 

 better method is to wrap a small piece of the foil about the 

 end of the electrode, or to attach to it a short gold wire. The 

 gold will be volatilized and deposited upon the walls of the 

 tube in a very thin layer, thus exposing a much larger surface 

 to the action of the mercurv vapor, in the manner described 

 below. 



In some of these experiments the tube under examination 

 was so placed that the gold lay at the bottom of the upper 

 portion, at the point where the 'capillary part is attached. In 

 this position it was exposed to the action of the more intense 

 discharge through the narrow part, and after a time it was 

 found that a lustrous and coherent film was deposited upon the 

 glass, the gold having evidently been volatilized by the elec- 

 tricity and condensed upon the walls of the fcube. In order to 

 study more conveniently the coa h the best 



effects might be produced, a loose roll of the foil was placed in 

 the middle of a tube about five millimeters in caliber, having a 

 branch near one end for the purpose of withdrawing the air, 

 and with pi. .sorted into the en. Is. This was 



exhausted until a discbarge from an induction coil passed read- 

 ily, when it was found that the gold was speedily deposited 

 upon the tube as be; - the foil along, a con- 



is area was cov ered with it in a short time. It appeared, 

 even under the microscope, as a perfectly continuous film, 

 forming a brilliant mirror, and showing the characteristic green 

 Am. Joub. Sci. -Third Sri -Jab., 1877. 



