548 



TABLE 572.— INFRARED REFLECTION OF SOLIDS (percent) 



Description of reflector 22.9/t 32.8/1 



Deposit of MgO from burning Mg ribbon 



Reflection /3-MgO 80 33 



Mica 32 



Paraffin 04 



Pencil mark on paper 09 



f Soot coating 43 48 



c ., . ... I MgO coating 08 91 



Silver covered with^ Zn * coatJng * 01 S2 



I Optical black 31 



Gold foil blackened with bismuth > 19 



KBr + 1.5m CaF 2 deposited by evaporation 10 



KI -f 1.5/t CaF 2 deposited by evaporation 13 



TABLE 573.— ABSORPTION OF VARIOUS MATERIALS USED FOR 



BLACKENING RECEIVERS FOR MEASURING RADIATION OF 



DIFFERENT WAVELENGTHS 170 



Soot from a candle, acetylene, or camphor flame has been used and was found by Pfund 

 to be very good to wavelengths about 1.2m; beyond this to longer wavelengths the soot 

 becomes transparent until at about 11m. for a film about as thick as will work satisfactorily, 

 it transmits about 50 percent of the incident radiation. 



Very finely powdered metal such as zinc (4 parts Zn and 1 part Sb) and platinum were 

 found to be very good. Even for wavelengths of about 14m the Zn powder absorbed over 

 98 percent of the radiation and out to 51m the absorption was about 85 percent. 



For longer wavelengths powdered NaCl, KBr, TICs, and some other salts were found to 

 be very good, as shown in the table. 



The figures given in the table for radiation absorption are relative, those with the highest 

 values being the blackest. For instance, India ink and tellurium powder are the best 

 absorbers for radiation shorter than 5m while for longer wavelengths than 50m powdered 

 glasses and CuSO« are probably the more nearly black. 



The absorptive power is an integrated effect over the entire far infrared. Litharge, 

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

 absorbers beyond 50m- A very thin coat of the absorbing material in most cases was an 

 inefficient absorber of the extreme infrared 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. Sixty-fold sensitiveness and better steadiness comes from evacua- 

 tion. 



The high absorption of glass in the near infrared suggests its use as a source of radiation. 

 Two Pt wires separated by 4 mm and covered with glass were heated by an electric cur- 

 rent ; the hot portion of the glass between the wires served as a source of extreme infrared 

 radiation. A convenient method of filtering out the near infrared is to grind the windows 

 with emery so that the pits are about 4m deep. The apparatus may be adjusted with visible 

 light by covering the rough surface with turpentine. 



Radiation 

 absorbed for 



Substance \<S/i \>50# 



Litharge 10.8 4.3 



Ground glass 11.9 4.7 



Powdered glass 11.7 5.0 



White lead 2 Pb 



C0 3 -Pb(OH) 2 14.9 4.9 



White lead in lacquer... 14.3 4.4 



Red phosphorus 18.3 5.0 



Red phosphorus from 



a match box 17.7 5.1 



Celestite, powdered 



SrSO, 14.7 4.6 



Brucite, powdered 



Mg(OH) 2 11.4 4.2 



Angelsite, powdered 



PbSO, 14.2 4.2 



Copper sulfide 17.1 5.2 



Copper oxide 13.8 4.4 



Radiation 

 absorbed for 



Substance \<5/n \>50/t 



Silver sulfide 12.8 4.4 



Copper sulfate crystals 



from solution 15.0 4.1 



Wellsbach mantle 



material 8.9 3 1 



Platinum black 18.2 4.4 



Tartaric acid and 



sugar 16.0 3.9 



Talc 12.5 3.8 



Water glass 12.1 3.7 



Tellurium, powdered . . . 19.2 3.3 



India ink 18.8 3.8 



Lacquer 8.6 3.0 



Castor oil 8.8 2 8 



Glycerine 1 1.2 3.1 



Turpentine 8.1 .2 



Clean receiver 2.9 .2 



170 Cartwright, Phys. Rev., vol. 35, p. 41S, 1930; Pfund, Rev. Sci. Instr., vol. 1, p. 397, 1930, and 

 Journ. Opt. Soc. Amer., vol. 23, p. 375, 1933. 



SMITHSONIAN PHYSICAL TABLES 



