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



In Faraday's experiments deposits of several different metals 

 upon plates of glass or other materials were obtained by passing 

 the spark from a Leyden battery between the points of wires 

 near the plates in an atmosphere of hydrogen. Films so ob- 

 tained are more or less irregular, and he describes them as 

 apparently not entirely continuous. Those formed by the 

 method ht.it deseril I however, are generally very uniform 

 and coherent, and even under the microscope appear to be per- 

 fectly continuous. For a study of the optical properties of the 

 metals they can be formed upon narrow slips of plane glass 

 introduced into the tubes by the side of the electrode. Simple 

 a Nicol's prism shows that these 

 films, at least in the case of gold, silver, iron, zinc and cadmi- 

 um, which have been tried by the writer, polarize the light 

 tii smitti 1 \ in , 1 1 \ , and the degree of polarization 



appears to increase with the incident angle as far as observa- 

 tion can be conveniently carried, which implies a very high 

 refractive index. It might be expected that the lighi should 

 be elliptical! . is point was not determined, and 



the optical properties of the films remain for further study. 



With respect to the relative energy of electrical action neces- 

 sary to volatilize the different metals the observations were 

 hardly precise enough to warrant the statement of a definite 

 law. Bismuth was volatilized most readily of all, gold and 

 silver with but slightly less facility. Platinum, palladium, 

 lead, tin, zinc and cadmium yield less readily, while copper, 

 froo, niol -charge and 



are volatilized with some difficulty. Aluminum requires an 

 energetic electrical action exerted for a long time, and the 

 electrode must be a quite fine wire. Magnesium is acted upon 

 still less readily, and is by far the most difficult, of all the 

 metals tried, to be obtained in the state of a thin layer. £ 

 cess was attained by the use of an energetic battery of fiv( 

 six Grove cells, with a coil capable of giving two-inch spai 

 the electrode being a wire cut from a thin ribbon of the metal 

 and not more than one-fifth of a millimeter in thickne 

 Even then no effect was produced till this was enclosed ii 

 very narrow tube by which the electrical action was cone 

 trated. The electrode itself appeared bright green, showi 

 that the discharge did act upon the metal, forming a tl 

 envelope of vapor about it, which did not reach the glass Ik 

 ever until the power of the current was increased and the size 

 of the tube considerably diminished. It will be seen that the 

 heavy metals, that is, those with high atomic weights, are most 

 readily volatilized, while those with smaller atomic weights 

 oppose great resistance to the electrical action, and those wish 

 medium weights occupy an intermediate position; but the 



