50 A. W. Wright— Production of Transparent Metallic Films 



color by transmitted light very beautifully. "When the tube 

 was afterwards rather strongly heated the gold lost its mirror- 

 likv surface in the thinner parts, assuming a frosted appearance, 

 and the light passed through it had a fine ruby color, conform- 

 ing in this to what was observed by Faraday in his experiments 

 on the relation of metals to light.*' A singularity in the result 

 was the fact that the volatilization occurred only' at that end of 

 the foil which was made a negative pole. This was observed 

 to be the case in all the subsequent experiments, except that 

 in one or two instances where a powerful discharge had been 

 ed for a considerable time a very slight deposit was 

 observed at the positive end also. 



As the matter appeared to be of interest with respect to its 

 furnishing a uew method of producing transparent metallic films, 

 the investigation was extended to a considerable number of 

 metals. Various forms of tubes were employed in successive 

 trials, but the method found most advantageous was the fol- 

 lowing: clean tubes of white glass, about "fifteen centimeters 

 in length, and with a caliber of from four to six millimeters, 

 were provided in the middle with a small branch tube for 

 attachment to the pump. In the ends were placed the elec- 

 trodes formed of the metals to be examined. These were gen- 

 erally in the form of thin wires from one-fourth to one-half a 

 millimeter in thickness. About one centimeter of this was 

 enclosed in a thin glass tube about three centimeters long, 

 drawn out of the same piece as the main tube, and made so 

 fine at the end as just to receive the wire. A platinum wire 

 was placed in the other end, so as to touch the first wire, and 

 sealed in. This was then carefully sealed into the end of the 

 main tube, the electrode being in its axis, and the platinum 

 wire projecting. It was necessary to cover the latter thus in the 

 interior to prevent its giving a deposit upon the tube with the 

 metal under examination. The tube was now exhausted to a 

 tension of one or two millimeters, or so far that, when the 

 discharge from the induction coil was passed through it, the 

 glow surrounding the negative pole filled the tube along the 

 whole extent of the electrode. After the coil had been put in 

 operation for a few minutes a deposit was formed upon the 

 glass, appearing at first as a mere darkening or discoloration, 

 which, gradually becoming deeper, finally began to show metallic 

 luster, while still suffering the light to pass freely. In almost 

 all cases it covered the whole area of the glass opposite the 

 electrode, but did not extend much beyond it After the film 

 was sufficiently developed the small branch was closed with a 

 gas flame, the tube drawn off, and sealed. 



* Experimental Researches in Chemistry and Physics. 



