ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



349 



analysis, and in particular gives an account of Zeiss's specially-designed 

 apparatus. 



Fig. 63 represents a suitable filter, the optical part of which consists 

 of a kind of two-chambered cuvette formed of three glasses cemented 

 together and kept in proper position by a brass frame. The glass used 

 is Jena blue-violet glass, one chamber being filled with a 20 per cent, 

 aqueous solution of copper-sulphate. A small glass syringe with an 

 indiarubber-tube extension is found to be the best means of carrying out 

 the filling and emptying, which should be done on each occasion of use. 



CA8LZE.ISS J£;-A 



Fig. 63. 



Fig. 64. 



The other chamber contains a dilute aqueous solution of nitrosodimethyl- 

 anilin. The ultra-violet transparency of the whole arrangement lies in 

 the interval from 400-300 /x/x, the maximum being about 350 fxfx. In 

 cases where the heat is likely to cause vaporisation of the copper- 

 sulphate a circulating arrangement of the sulphate (fig. 68) is substituted 

 for the above. The apparatus is adjustable in height, and may be used 

 with a circular base or with a rider on an optical bench. 



Fig. 64 shows the lenses best adapted for the U V-filter. The best 

 material is quartz, but for many purposes Jena U V-glass does very well, 

 and is much cheaper. The lenses recommended have a diameter o( 

 40-100 mm. and a focal length of 80-200 mm. 



As a liglit-source an electro-incandescent lamp is of little use. A 



