Tables 45 and 46 



TABLE 45. — Reductions of Weighings in Air to Vacuo 



IO9 



When the weight M in grams of a body is determined in air, a correction is necessary for the 

 buoyancy of the air equal to M 5 (i/d— i/d,) where 5 = the density (wt. of 1 ccm in grams 

 = 0.0012) of the air during the weighing, d the density of the body, d, that of the weights. 

 8 for various barometric values and humidities may be determined from Tables I28tO 130. The 

 following table is computed for 5 = 0.0012. The corrected weight = M + kM/1000. 



TABLE 46.— Reductions of Densities in Air to Vacuo 

 (This correction may be accomplished through the use of the above table for each separate 

 weighing.) 



If s is the density of the substance as calculated from the uncorrected weights, S its true den- 

 sity, and L the true density of the liquid used, then the vacuum correction to be applied to the 

 uncorrected density, s, is 0.0012 (1 — s/L). 



Let W s = uncorrected weight of substance, Wi = uncorrected weight of the liquid displaced 

 by the substance, then by definition, s= LW s /Wi. Assuming D to be the density of the 

 balance of weights, \V S {1 4- 0.0012 (i/S — i/D)}and Wi {1 +0.0012 (i/L — i/D) }are the 

 true weights of the substance and liquid respectively (assuming that the weighings are made 

 under normal atmospheric corrections, so that the weight of 1 cc of air is 0.0012 gram). 



Then the true density S = 

 But from above W s /Wi = 



W s {i + 0.0012 (i/S — i/D) } 



1.. 



Wl{l + 0.0012 (i/L— i/D)} 



s/L, and since L is always large compared with 0.0012, 



S — s = 00012 (1 — s/L). 

 The valuer of 0.0012 (1 — s/L) for densities up to 20 and for liquids of density I (water), 

 O.852 (xylene) and 13.55 (mercury) follow : 



(See reference below for discussion of density determinations). 



Johnston and Adams, J. Am. Chem. Soc. 34, p. 563, 1912. 



Smithsonian Tables. 



