392 Notes. 



On a Method of Obtaining Monochromatic Ultra-violet Light. 

 By E. B. Stringer, B.A., F.R.M.S. 



In a paper read before the Society at the April meeting last year,* 

 I pointed out the advantage of using the electric arc itself as a 

 source of light in photomicrography, and showed how a mono- 

 chromatic violet light might be obtained, by isolating the violet 

 band of the arc spectrum by the use of solutions of ammonia 

 sulphate of copper and quinine. I have since found a means of 

 separating the two ultra-violet bands from the visible rays ; and 

 also of isolating one of them so as to obtain monochromatic ultra- 

 violet light. 



A solution of uranic sulphate is completely opaque to the 

 visible violet band of the arc spectrum, whilst freely transmitting 

 the two ultra-violet bands ; so that if this be used with the 

 ammonia copper solution instead of the quinine, we get the ultra- 

 violet rays alone. A solution of uranic acetate, on the other hand, 

 transmits only the first or less refrangible ultra-violet band; this, 

 therefore, gives monochromatic ultra-violet light — as one may be 

 allowed to call it, though of course it has no colour, appearing on 

 the screen of a pale grey or neutral tint. 



Lenses corrected so as to work with it would be a considerable 

 gain, and might easily be used ; the focal adjustment being made 

 by the visible violet rays, before the introduction of the uranium 

 solution. Its mean wave-length is about 3760, that of the visible 

 violet band being 4190. 



Of course the prism is not used when actually working with 

 the Microscope, the troughs of solution being placed in the path 

 of the direct beam from the arc. Such a comparatively weak 

 source of light as the arc itself cannot be used well, without the 

 concentration afforded by the condensing system which I described 

 in a previous paper. 



In order to get both bands with the uranic sulphate it is better 

 to use a solution of methylen-blue to which copper sulphate has 

 been added, instead of the ammonia copper solution. The object 

 of the copper sulphate is to cut off the extreme red which the 

 methylen-blue transmits. This solution may also be used with 

 Ihe acetate, and is better than the ammonia copper for both 

 purposes. 



Using a quartz prism and lenses, a trough having quartz sides, 

 iind a fluorescent screen of uranic phosphate, both the uranium 

 solutions are found to cut off all the rest of the ultra-violet 



* See this Journal, WW, p. 270. 



