preface to fifteenth edition

GENERAL INFORMATION, CONVERSION TABLES, AND MATHEMATICS 2.83
TABLE 2.14
Conversion of Weighings in Air to Weighings in Vacuo
If the mass of a substance in air is m f , its density m , the density of weights used in making the weighing
w , and the density* of air a , the true mass of the substance in vacuo, m vac,
is
1 1
mvac mf amf
For most purposes it is sufficient to assume a density of 8.4 for brass weights, and a density of 0.0012 for
air under ordinary conditions. The equation then becomes
1 1
mvac mf 0.0012mf
8.4
m
w
The table which follows gives the values of k (buoyancy reduction factor), which is the correction necessary
because of the buoyant effect of the air upon the object weighed; the table is computed for air with the density
of 0.0012; m is the weight in grams of the object when weighed in air; weight of object reduced to “in
vacuo” m km/1000.
Density of
object weighed
Brass weights,
density 8.4
m
Buoyancy reduction factor, k
Pt or Pt-Ir
weights, density 21.5
Al or quartz weights,
density 2.7
Gold weights,
density 17
0.2 5.89 5.98 5.58 5.97
0.3 3.87 3.96 3.56 3.95
0.4 2.87 2.95 2.55 2.94
0.5 2.26 2.35 1.95 2.34
0.6 1.86 1.95 1.55 1.93
0.7 1.57 1.66 1.26 1.65
0.75 1.46 1.55 1.15 1.53
0.80 1.36 1.45 1.05 1.43
0.82 1.32 1.41 1.01 1.39
0.84 1.29 1.37 0.98 1.36
0.86 1.25 1.34 0.94 1.33
0.88 1.22 1.31 0.91 1.29
0.90 1.19 1.28 0.88 1.26
0.92 1.16 1.25 0.85 1.24
0.94 1.13 1.22 0.82 1.21
0.96 1.11 1.20 0.80 1.18
0.98 1.08 1.17 0.77 1.16
1.00 1.06 1.15 0.75 1.13
1.02 1.03 1.12 0.72 1.11
1.04 1.01 1.10 0.70 1.08
1.06 0.99 1.08 0.68 1.06
1.08 0.97 1.06 0.66 1.04
1.10 0.95 1.04 0.64 1.02
1.12 0.93 1.02 0.62 1.00
1.14 0.91 1.00 0.60 0.98
1.16 0.89 0.98 0.58 0.96
1.18 0.87 0.96 0.56 0.95
1.20 0.86 0.95 0.55 0.93
1.25 0.82 0.91 0.51 0.89
1.30 0.78 0.87 0.47 0.85
* See Table 5.15, Specific Gravity of Air at Various Temperatures.