538 



TABLE 563.— ULTRAVIOLET TRANSPARENCY OF ATMOSPHERIC COMPONENTS 



/ = /. 10-"", d in cm 0°C, 760 mmHg. 



Air at sea level (Washington), 400 m practically no absorption X > .3^; < .28m about that 

 due to molecular scattering. Air transmission reduced by 1/100: 22 km at .28m; 5 at 25m; 0.57 at 

 .22m ; 20 km at .205m. 



Atmospheric transparency for ultraviolet 



Wavelength, m 29 



Percent transmitted . . 



TABLE 564.— TRANSMISSION OF DYESTUFF SOLUTIONS OF 

 "ADJUSTED" CONCENTRATIONS* 



The table gives the percentage transmittances (column 5) at various wavelengths, of the 

 dye solutions, dissolved or buffered as indicated in the third column. All solutions are ad- 

 justed to that concentration which gives unit density (10-percent transmittance) at the 

 wavelength of maximum absorption, except for those solutions (marked * in column 4) 

 that have the maximum absorption in the ultraviolet range. The wavelength of maximum 

 absorption is given in column 2. In column 3 is given the serial number of the dye as 

 listed and described in the Colour Index of the British Society of Dyers and Colorists 

 (1924). Dyes having no Colour Index number are listed by the "prototype number" 

 (abbreviated Pr.) of the 1949 Technical Manual and Year Book of the American Associa- 

 tion of Textile Chemists and Colorists, p. 147. The names assigned to the dyes are not the 

 names used by the individual American manufacturers but are older names assigned by 

 the Year Book to each Colour Index number, p. 237; or to the "foreign prototype," p. 261. 



In column 4, A stands for acid buffer (pH = 4.6), K for alkaline buffer (pH = 9.3). 

 In this column, E stands for ethanol (ethyl alcohol) used as solvent, and Bz for benzene. 

 Where A or K are used, the solvent was water. TV stands for "no buffer," with water as 

 solvent. 



In some cases two or more sets of transmissions correspond to a given Colour Index 

 number and name. For example, C.I. No. 326 corresponds to 62 dyestuffs listed as on the 

 American market in 1939, and these may be classified as of several distinct types of Benzo 

 Fast Scarlets and Benzo Fast Qranges. In less striking cases, the different types result 

 from uncontrollable variations in manufacture. In such cases, the transmissions should be 

 considered as representative rather than as specifications of the dye. No manufacturer 

 would guarantee the transmissions within a narrow range, though all data are accurate 

 measurements on actual representatives of at least one manufacturer's products. Trans- 

 missions vary somewhat with the exact pH of the buffer and with the characteristics of 

 the instrument used for measurement, especially with the slit width. The present data 

 obtained with the General Electric recording spectrophotometer, which has a 10-micron 

 slit width. 



From the data of the table, approximate data for stronger solutions, whose transmission 

 at the wavelength of maximum absorption is only 1 percent, may be readily obtained by 

 means of a table of squares. Such solutions are twice as concentrated as those of the table. 

 Their transmissions at any given wavelength are approximately the squares of the tabu- 

 lated transmissions. These relations depend on the validity of Beer's Law for the solution 

 in question. 



* Data furnished by I. H. Godlove, General Aniline & Film Corporation. 



(.continued) 

 SMITHSONIAN PHYSICAL TABLES 



