46 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 68 



B. ABSORPTION IN WATER VAPOR AND CARBON DIOXIDE FOR WAVE- 

 LENGTHS 1.2 TO 9.0 fi 



(l) LABORATORY CONDITIONS APPROACHING ATMOSPHERIC CONDITIONS AS TO TEM- 

 PERATURE, TOTAL AND PARTIAL PRESSURES 



Observations described in the main body of this report were made 

 in a 60° -prismatic rock-salt spectrum, of the effect of water vapor 

 and carbonic-acid gas to deplete energy from the radiation of a 

 Nernst lamp (at 2,200° K.) in this spectrum region. The absorbents 

 comprised in some experiments 0.008 cm. ppt. H^O and carbon 

 dioxide of such an amount that there would have been 7.4 grams in 

 a column the length of the path and a meter square in section ; and 

 in other experiments 0.082 cm. ppt. H„0 and 83 grams of carbon 

 dioxide. For mental comparison, the total amount of carbon dioxide 

 similarly measured vertically from the surface of the earth outwards 

 is about 3,000 grams. 



The appearance of the absorption bands in the energy curve of 

 the lamp is shown in the lower half of figure 6. The computed 

 percentage absorptions are given in figure 7. The percentage ab- 

 sorptions in regions extending over various wave-length ranges are 

 given in table 4. Paschen's results for carbon dioxide are given 

 in table 3. It is through table 4 that the results are most easily apph- 

 cable. The amount of radiation available before absorption between 

 the wave-lengths indicated in column 2 should be multiplied by the 

 ratio belonging to the proper amount of ppt. HoO taken from the 

 columns headed " percentage absorbed " and the result will be the 

 amount lost in the corresponding water vapor. Table 4 may be 

 supplemented for greater amounts of vapor by the data in table 6 

 obtained from the observations with the 15° rock-salt prism. 



(2) RESULTS FOR STEAM (l.2 TO Q.O ^) 



The results obtained by Paschen for steam are given in the Annalen 

 der Physik und Chemie, 52, p. 209, 1894. In figure 7 are shown the 

 results for the water-vapor absorption band from 5 to 8 /a. With 

 equal quantities of ppt. H2O, water vapor in the form of steam 

 evidently produces considerably more absorption than when dispersed 

 at small partial pressure as in the atmosphere, even although the 

 same total pressure prevails. Referring to figure 7 the partial 

 pressure of Paschen's steam (at 100° C.) was equal to its total 

 pressure, 76 cm. The partial pressure of water vapor in the present 

 research (at 20 to 30° C.) was of the order of a centimeter, the total 

 pressure 76 cm. 



