380 Tab, - e 107 



relative humidity over saturated salt solutions 1 



A convenient method for calibrating hygrometers is by use of certain saturated salt 

 solutions in a sealed chamber. The chamber should be kept free from water-absorbing 

 materials, such as wood. The salt solution is made up as a slushy mixture, with the solu- 

 tion spreading over as large an area as possible, and a method should be provided for 

 circulating the air within the chamber. Distilled water and chemically pure salts must 

 be used. Even with these precautions it is emphasized that the tabulated values of rela- 

 tive humidity can be considered as only approximate, and for precision work must be 

 checked by independent measurements. 



1 Nat. Bur. Stand. Letter Circ. LC 946, March 31, 1949. 

 F. E. M., Journ. Sci. Instr., vol. 25, p. 73, 1948. 



For a more complete table see O'Brien, 



SMITHSONIAN METEOROLOGICAL TABLES 



