266 G. F. Becker—Correction for Vacuum in Chemical Analysis. 
ancy of the atmosphere while others have laid the greatest 
stress upon it. 
Consistency among chemists in the treatment of this source 
of error is certainly desirable. The subject is a simple one and 
the cases in which the correction is of importance are so readily 
distinguished from those in which it is insignificant as to repay 
the small amount of thought necessary to discriminate them. 
If w = the apparent weight of a body; 
w,= the true weight; 
y = its specific gravity ; 
d = the specific gravity of the weights, and 
¢ = the weight of one cubic centimeter of air; then 
= wa 
Y Sais Yy d : 
If the necessary correction is x 
L=w,—W; 
and if the apparent weight is one gram, 
a 
y 
If c and d are regarded as constants, this equation represents 
an hyperbola referred to axes parallel to its asymptotes. 
It will readily be seen that the form of the curve is indepen- 
dent of d, or the material of which the weights are made, this 
constant simply determining the position of the axis of y, for 
«x= 0 
| y=d 
The curve is plotted (figure, page 269,) for d = 21%, the 
specific gravity of platinum, and ¢ = 0-001225761, the weight 
of one cubic centimeter of dry air with the normal carbonic ac! 
contents, at 45° of latitude, the normal pressure, and a temper- 
ature of 15°. The abscissz in the diagram represent the cor- 
rection for atmospheric displacement necessary per gram 1 
tenths of milligrams. The ordinates represent the correspond- 
ing specific gravities. A glance shows that for high specific 
ielbibee: the correction is small and changes but slowly, while 
for specific gravities but little in excess of 1, the correction 
is comparatively large and increases with great rapidity as the 
oe gravity sinks. This is expressed algebraically by the 
a 
form 
ws. ¥ 
Gece? 
which indicates that the error decreases in proportion to the 
increase of the square of the ific gravity, or that the inter- 
vals through which the specih © gravity may be 
constant decrease as the square of the specific gravity decreases. 
