230 Pennington — A Cliemico-Physiological 



centration. This is obtained by dissolving 0.888 grains of 

 mandarin in 1000 cc. of water. A layer of \S/s inches is 

 necessary. The copper sulphate is a solution saturated at 

 the ordinary temperatures, and is used in a 1^3 inch layer. 



For this screen, therefore, we require two glass dishes, 

 one above the other. The wave lengths obtained are from 

 603 fifi. to 579 fj.fi. 



Orange. — This screen was made much like the preced- 

 ing one. For the orange, however, a stronger solution of 

 the mandarin orange is necessary, and a weaker copper 

 sulphate solution, since the portion of the spectrum desired 

 now includes rays which are less refrangible than the yel- 

 low. These solutions are : 



*• 3-333 grams mandarin in iodo cc. of water. The 

 layer should be 1^ inch. 



2. 160 grams copper sulphate in 1000 cc. of water. The 

 layer should be one inch. 



The light passing through these two solutions is entirely 

 absorbed with the exception of a narrow band which 

 extends from 634 ftp. to 599 fifi. 



Red. — The band in this case may be obtained by the use 

 of an aqueous solution of a scarlet aniline dye. This dye 

 consists of a mixture of equal parts of (1) the soda salt 

 of xylidin-azo-B-naphthol-sulphonic acid, and (2) sodium 

 mono-sulphonate of amido-azo- benzol -azo-B-naphthol. 

 Technically, it is known as "Scarlet, [(SRRB) (BASF)]," 

 and serves as a wool dye. Of this 12 grams should 

 be dissolved in 1000 cc. of water, and the glass dish 

 filled to the depth of one inch. The red band extends 

 from 718 fifi. to 643 fifi. 



It will be seen that, with the exception of the yellow and 

 orange screens, a single layer suffices for the attainment of 

 the desired wave lengths. The yellow and orange, occupy- 

 ing so short a portion of the visible spectrum, have been 

 found to be unsatisfactory unless produced as above de- 

 scribed. The wave lengths as given are for the orange 

 from 634 fj.fi. to 599 fifi., and for the yellow from 603 fifi. to 



