Tables 41-42. 



REDUCTIONS OF WEIGHINGS IN AIR TO VACUO. 



TABLE 41. 



73 



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/dj) where 5 ^ the density (wt. of i 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 153 to 155. The 

 following table is computed for S = o.ooj 2. The corrected weight = M + kM/iooo. 



TABLE 42.— Reductions of Densities In Air to Vacuo. 

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

 weighing.) ^ . , r. • 



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 (i — s/L). 



Let Ws = uncorrected weight of substance, Wi = uncorrected weight of the liquid displaced 

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

 balance of weights, Ws {i +C.0012 (r/S — i/D)}and Wi (i +0.0012 (i/L — i/D)}arethe 

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

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



Ws{i + 0.0012 (i/S — i/D) } 



Then the true density S = L. 



Wl{i + 0.0012 (i/L— i/D)} 



But from above Ws/Wi = s/L, and since L is always large compared with 0.0012, 



S — s = 0.0012 (1 — s/L). 

 The values of 0.0012 (i — s/L) for densities up to 20 and for liquids of density i (water), 

 0.852 (xylene) and 13.55 (mercury) follow : 



(See reference below for discussion of density determinations). 



Smithsonian Tables. 



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



