JOURNAL 



OF THE 



WASHINGTON ACADEMY OF SCIENCES 



Vol. II, NOVEMBER 19, 1912 No. 19 



PHYSICS. — The diffuse reflecting power of various substances. 

 W. W. Coblentz, Bureau of Standards. To appear in full 

 in the Bulletin of the Bureau of Standards. 



This paper gives an account of an investigation of the reflect- 

 ing power of matte surfaces of various substances, for the spectral 

 regions of 0.54, 0.60, 0.95, 4.4, 8.8, and 24/*. The diffusely re- 

 flected radiations were collected by means of a hemispherical 

 mirror, and projected upon a surface thermopile of bismuth and 

 silver, which was used to measure the intensity of the incident 

 and reflected radiations. 



The substances examined include lampblack, platinum black, 

 pigments, white paints, green leaves, dyed cloth, and building 

 material. The object of the investigation was to find the blackest 

 and the whitest substances; the former to be used as absorbing 

 surfaces of radiometers, the latter to be used as a covering for 

 buildings exposed to intense sunlight. 



Methods are given for preparing standard black surfaces; and 

 quantitative data are given for the loss by reflection of the same. 

 The blackest deposits of soot are obtained from an acetylene 

 flame; the reflecting power being only about 0.6 per cent. Lamp- 

 black paint made by mixing the dry material with turpentine 

 reflects about 3 per cent in the visible spectrum to 3.5 per cent 

 in the extreme infra-red. Thick deposits of platinum black 

 reflect about 1 per cent in the visible spectrum and 2 to 3 per 

 cent in the extreme infra-red. 



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