384 Tables 435 and 436 



For classification of various light and radiation filters with bibliography, plots, and dis- 

 cussions, see Gibson, Spectral Filters, Journ. Opt. Soc. Amer., 13, 267-280, 1926. 



Filters for the reproduction of sunlight and daylight and the determination of color 

 temperatures, see Davis, Gibson, Bur. Standards Misc. Publ. 114, 1931. 



TABLE 435. — Light Filters, Narrow Spectrum Regions 



(Jones, Journ.- Opt. Soc. Amer., 16, 259, 1928. Filters from the following components: 

 Distilled H 2 ; Aq. sol. CuSO*-5H 2 0; NiS04-7H 2 0; Glasses, Corning G 986A, G 586, 

 G 980A ; dyed gelatin, Wratten filters 88A, 25, 6i, 49.) 



Concentration 

 Filter and Absorbent thickness 



88A 



88A, H 2 2 cm 



88A, G 986A .32 cm 



25, CuS0 4 • 5H 2 5%, 2 cm 



61, 5%, 2 cm 



49, " 5%, 2 cm 



G 586, " 32 cm ; 10%, 2 cm 



G 986, NiSOi • 7ILO 32 cm ; 50%, 1 cm 



TABLE 436. — Absorbing Power of Various Materials — Infra-red. 

 (Cartwright, Phys. Rev., 35, 4*5, 1930.) 



The absorptive power is an integrated effect over the entire far infra-red. Litharge, 

 powdered glass, white lead, copper sulphide, celestite, and red phosphorus were the best 

 absorbers beyond 50/*. A very thin coat of the absorbing material in most cases was an 

 inefficient absorber of the extreme infra-red waves. A very poor absorbing material in 

 most cases such as copper or platinum will absorb if the surface is sufficiently rough. 



For radiometers, the absorbing material is better when mixed with turpentine and 

 alcohol and painted on the vanes. For thermocouples, the absorbing material is better if it 

 is mixed with lacquer. 60-fold sensitiveness and better steadiness comes from evacuation. 



The high absorption of glass in the near infra-red suggests its use as a source of radia- 

 tion. Two Pt wires separated by 4 mm and covered with glass were heated by an electric 

 current ; the hot portion of the glass between the wires served as a source of extreme infra- 

 red radiation. A convenient method of filtering out the near infra-red is to grind the 

 windows with emery so that the pits are about 4/a deep. The apparatus may be adjusted 

 with visible light by covering the rough surface with turpentine. 



Substance 



Radiation absorbed for 

 X<5/i X>50/t 

 V I I/V 



Litharge 10.8 4.3 .40 



Ground glass 11.9 47 -4° 



Powdered glass 11.7 5-0 -43 



White lead 2 Pb 



C0 3 -Pb(OH) 2 .. 14.9 4-9 -33 



White lead in lacquer 14.3 4.4 -3* 



Red phosphorus 18.3 5.0 .27 



Red phosphorus from 



a match box 17.7 5.1 .29 



Celestite, powdered 



SrS0 4 147 4-6 .31 



Brucite, powdered 



Mg(OH) 2 11.4 4-2 -37 



Angelsite. powdered 



PbSOi 14-2 4-2 .30 



Copper sulphide 17.1 5-2 .30 



Copper oxide 13-8 4-4 -3 2 



Substance 



Radiation absorbed for 

 X<5A \>50/i 

 V I I/V 



Silver sulphide 12.8 4.4 .34 



Copper sulphate crys- 

 tals from solution. 15.0 4.1 .27 

 Wellsbach mantle 



material 8.9 3.1 .35 



Platinum black 18.2 4.4 .24 



Tartaric acid and 



sugar 16.0 3.9 .24 



Talc 12.5 3.8 .30 



Water glass 12.1 3.7 .31 



Tellurium, powdered. 19.2 3.3 .17 



India ink 18.8 3.8 .20 



Lacquer 8.6 3.0 .35 



Castor oil 8.8 2.8 .32 



Glycerine 11.2 3.1 .28 



Turpentine 8.1 0.2 .02 



Clean receiver 2.9 0.2 .07 



Smithsonian Tables 



