TABLES 190-191. 

 TRANSMISSIBILITY FOR RADIATION. 



TABLE 190. Color Screens. 



195 



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, 48.- (Berlin Anilin Fabrik) very dilute, and nitroso-dimethyl-anilme transmits 0.365/4. 



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



blot out 0.4359/4, transmits 0.4047 and 0.4048, also faintly 0.3984. 

 Cobalt glass -f- aesculin solution transmits 0.4359/4. 

 Guinea green B extra (Berlin) -j- chinin sulphate transmits 0.4916/4. 

 Neptune green (Bayer, Elberfeld) + 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- cosine transmits 0.5790/4. The former should be dilute and the cosine 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 passes 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 O.5O-.53/4; addition of CaCl 2 widens the band to 

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

 alcohol -f water, absorbs O-5O-.53 and everything below 0.35. In methyl alcohol alone 0.485- 

 0.555 an d below 0.40/4. 



Copper chloride : in ethyl alcohol absorbs above 0.585 and below 0.535 '> m alcohol + 50% water, 



above 0.595 and below 0.37/4. 

 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 0.60/4, 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-.485/4. Absorption below 0.34. 

 Picric acid absorbs o. 36-42/4, depending on the concentration. 

 Potassium chromate absorbs O.4O-.35, O-3O-.24, transmits 0.23/4. 



* Potassium permanganate: absorbs 0.5 5 5-. 50, transmits all the ultra-violet. 



Chromium chloride : absorbs above 0.57, between 0.50 and .39, and below 0.33/4. These limits 



vary with the concentration. 

 Aesculin : absorbs below 0.363/4, very useful for removing the ultra-violet. 



* Nitroso-dimethyl-aniline : very dilute aqueous solution absorbs O.49-.37 and transmits all the 

 ultra-violet. 



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



everything below 0.70 and transmits freely the red. 

 Iodine : saturated solution in CS 2 is opaque to the visible and transparent to the infra-red. 



SMITHSONIAN TABLES. 



