550 



TABLE 576.— REFLECTING FACTOR OF POWDERS (WHITE LIGHT) 



(percent) 



Various pure chemicals, very finely powdered and surface formed by pressing down 



with glass plate. White (noon sunlight) light. Reflection in percent. 



Aluminum oxide 83.6 Rochelle salt 79.3 



Barium sulfate 81.1 Salicylic acid 81.1 



Borax 81.6 Sodium carbonate 81.8 



Boric acid 83.2 Sodium chloride 78.1 



Calcium carbonate 9St Sodium sulfate 77.9 



Citric acid 81.5 Starch 80.3 



Magnesium carbonate 86.6 Sugar 87.8 



(block)... 94-97t Tartaric acid 79.1 



Magnesium oxide (6 mm. thick). 98*t 



* The smoke of magnesium turnings freely burning in air and deposited on a satisfactory base forms 

 a uniform fine-grained diffusing surface of high reflectance. This oxide should be deposited so as not 

 to be affected by the heat from the burning Mg. A satisfactory base may be Al, silver-plated Cu, block 

 porcelain. The oxide adheres better to depolished surfaces. Surfaces of high and uniform reflectance 

 throughout the spectrum are best. t Revised values. 



TABLE 577.— VARIATION OF REFLECTING FACTOR OF SURFACES 

 WITH ANGLE (RELATIVE VALUES) 



Illumination at normal incidence, 1^-watt tungsten lamp, reflection at angles indicated 

 with normal. 



Angle of observation 0° 1° 3° 



Magnesium carbonate block 88 — — 



Magnesium oxide 80 — — 



Matt photographic paper 78 — — 



White blotter 76 — — 



Pot opal, ground 69 .69 .69 



Flashed opal, not ground 11.3 11.3 11.3 



Glass, fine ground 29 .29 .29 



Glass, coarse ground 23 .22 .21 



Matt varnish on foil 83 — .78 



Mirror with ground face 4.9 — — 



The following figures, taken from Fowle, Smithsonian Misc. Coll., vol. 58, No. 8, in- 

 dicate the amount of energy scattered on each side of the directly reflected beam from a 

 silvered mirror ; the energy at the center of the reflected beam was taken as 100,000, and 

 the angle of incidence was about 3°. 



Angle of reflection, 3° ± 0' 8' 



Energy 100,000 600 



Wavelength of max. energy of Nernst lamp used as source about 2/i. 



TABLE 578.— ULTRAVIOLET REFLECTING FACTOR OF SOME METALS 1 " 



.250/* .300 



Aluminum, cast polished 43 .45 



rolled 21 .28 



Rhodium 30 .37 



Tin, polished 33 .38 



Duralumin 24 .31 



tarnished to 20 .26 



171 Coblentz, Stair, Nat. Bur. Standards Journ. Res., vol. 4, p. 189, 1930. 



SMITHSONIAN PHYSICAL TABLES 



