TABLES 556-573.— TRANSMISSION OF RADIATION 535 



TABLE 556.— COLOR SCREENS 



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

 prepared solutions. 



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



Methyl violet, 4^- (Berlin Anilin Fabrik) very dilute, and nitroso-dimethyl-aniline trans- 

 mits 0.365/x. Methyl violet + chinin-sulfate (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 + aesculin solution transmits 0.4359m. 



Guinea green B extra (Berlin) -+- chinin sulfate transmits 0.4916m- 



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

 mit 0.5790 and 0.5461 ; then add the Neptune green until the yellow lines disappear. 



Chrysoidine -f eosine transmits 0.5790m. 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 percent 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 

 ultraviolet. 



* Cobalt chloride : solution in water, absorbs 0.50-.53m ; addition of CaCl 2 widens the 

 band to 0.47-.50. It is exceedingly transparent to the ultraviolet 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 0.40m- 



Copper chloride : in ethyl alcohol absorbs above 0.585 and below 0.535 ; in alcohol + 50 

 percent water, above 0.595 and below 0.37m. 



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 

 0.60m, 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-.485m- Absorption below 0.34. 



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



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



* Potassium permanganate : absorbs 0.555-.50, transmits all the ultraviolet. 

 Chromium chloride : absorbs above 0.57, between 0.50 and .39, and below 0.33m- These 



limits vary with the concentration. 



Aesculin : absorbs below 0.363m, very useful for removing the ultraviolet. 



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

 all the ultraviolet. 



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 CS* is opaque to the visible and transparent to the infrared. 



SMITHSONIAN PHYSICAL TABLES 



