Tables 447 and 448 



TABLE 447. — Color Screens 



39 1 



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 448. — 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 0.365/t. 



Methyl violet -j- 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- ae^culin solution transmits 0.4359,11. 

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

 Neptune green (Bayer, Elberfeld) + chrysoidine. Dilute the latter enough to just transmit 0.579c 



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

 Chrysoidine + eosine transmits 0.5790/1. 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 0.50-.53/1; 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 -f- water, absorbs 0.50-.53 and everything below 0.35. In methyl alcohol alone 0.485- 

 0.555 and below 0.40/1. 



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



above 0.595 and below 0.37/1. 

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



bands. In solution with bichromate of potash, transmits o. 535-565 and above 0.60/t, 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-.4S5/1. Absorption below 0.34. 

 Picric acid absorbs o. 36-42/1, depending on the concentration. 

 Potassium chromate absorbs 0.40-.35, 0.30-.24, transmits 0.23/1. 



* 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 0.33/1. These limits 



vary with the concentration. 

 Aesculin : absorbs below 0.363/1, 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. 



