Tables 190-191. I95 



TRANSMISSIBILITY FOR RADIATION. 



TABLE 190. — Color Screens. 



The following light-filters are quoted from Landolt's " Das optische Drehungsvermogen, etc." 1898. 

 Although only the potassium salt does not keep well it is perhaps safer to use freshly prepared 

 solutions. 



TABLE 191. — Color Screens. 



The following list is condensed from Wood's Physical Optics, 2nd edition : 



Methyl violet, 4R- (Berlin Anilin Fabrik) very dilute, and nitroso-dimethyl-aniline transmits 0.365/*. 



Methyl violet -|- chinin-sulphate (separate solutions), the violet solution made strong enough to 



blot out 0.4359/*, transmits 0.4047 and ,0.4048, also faintly 0.3984. 

 Cobalt glass -j- aesculin solution transmits 0.4359/*. 

 Guinea green B extra (Berlin) -|- chinin sulphate transmits 0.4916/1. 

 Neptune green (Bayer, Elberfeld) -f chrysoidine. Dilute the latter enough to just transmit 0.5790 



and 0.5461 ; then add the Neptune green until the yellow lines disappear. 

 Chrysoidine -f eosine transmits 0.5790/*. The former should be dilute and the eosine added until 



the green line disappears. 

 Silver chemically deposited on a quartz plate is practically opaque except to the ultra-violet region 



0.3160-0.3260 where 90% of the energy pa.sses through. The film should be of such thickness 



that a window backed by a brilliantly lighted sky is barely visible. 

 In the following those marked with a * are transparent to a more or less degree to the ultra-violet: 



* Cobalt chloride : solution in water, — absorbs 0.50-.53/*; addition of CaClo widens the band to 

 0.47-.50. It is exceedingly transparent to the ultra-violet down to 0.20. If dissolved in methyl 

 alcohol -j- water, absorbs o. 50-53 and everything below 0.35. In methyl alcohol alone 0.485- 

 0.555 ^"<i below 0.40/*. 



Copper chloride : in ethyl alcohol absorbs above 0.585 and below 0.535 '> '" alcohol -f 50% water, 



above 0.595 and below 0.37/*. 

 Neodymium salts are useful combined with other media, sharpening the edges of the absorption 



bands. In solution with bichromate of potash, transmits 0.535-.565 and above 0.60/1, the bands 



very sharp (a useful screen for photographing with a visually corrected objective). 

 Praesodymium salts : three strong bands at 0.482, .468, .444. In strong solutions they fuse into a 



sharp band at o.435-.485/t. Absorption below 0.34. 

 Picric acid absorbs 0.36-.42/1, depending on the concentration. 

 Potassium chromate absorbs 0.40-.35, 0.30-.24, transmits 0.23/*. 



* Potassium permanganate : absorbs 0.55 5-. 50, transmits all the ultra-violet. 



Chromium chloride : absorbs above 0.57, between 0.50 and .39, and below o.33/t. These limits 



vary with the concentration. 

 Aesculin : absorbs below 0.363/*, very useful for removing the ultra-violet. 



* Nitroso-dimethyl-aniline : very dilute aqueous solution absorbs 0.49-.37 and transmits all the 

 ultra-violet. 



Very dense cobalt glass + dense ruby glass or a strong potassium bichromate solution cuts off 



everything below 0.70 and transmits freely the red. 

 Iodine : saturated solution in CS2 is opaque to the visible and transparent to the infra-red. 



Smithsonian Tables. 



