3o6 



Tables 373-374. 

 TRANSMISSIBILITY OF RADIATION. 



TABLE 373. — 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 374. —Color Screens. 



The following list is condensed from Wood's Physical Optics : 



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



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



blot out o.4359;u, transmits 0.4047 and .0.4048, also faintly 0.3984. 

 Cobalt glass -j- aesculin solution transmits o.4359)u. 

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

 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 -j- 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 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.50-.53(u; 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 -{■ water, absorbs o. 50-53 and everything below 0.35. In methyl alcohol alone 0.485- 

 0.555 and below 0.40/*. 



Copper chloride : in ethyl alcohol absorbs above 0.585 and below 0.535 5 '" alcohol -f- 50% water, 



above 0.595 and below o.37ja. 

 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 0.60/11, the bands 



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

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



sharp band at 0.435-485111. Ai-)sorption below 0.34. 

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

 Potassium chromate absorbs 0.40-.35, 0.30-.24, transmits 0.23/11. 



* 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/^. These limits 



vary with the concentration. 

 Aesculin : absorbs below 0.3631^, 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 CSj is opaque to the visible and transparent to the infra-red. 



Smithsonian Tables. 



