air before and after combustion, and
the quantity absorbed during the process.

_Calculation before Combustion._

The air in the jar before combustion was 353 cubical inches, but it was
only under a barometrical pressure of 27 inches 9-1/2 lines; which,
reduced to decimal fractions by Tab. I. of the Appendix, gives 27.79167
inches; and from this we must deduct the difference of 4-1/2 inches of
water, which, by Tab. II. corresponds to 0.33166 inches of the
barometer; hence the real pressure of the air in the jar is 27.46001. As
the volume of elastic fluids diminish in the inverse ratio of the
compressing weights, we have the following statement to reduce the 353
inches to the volume the air would occupy at 28 inches barometrical
pressure.

353 : x, the unknown volume, :: 27.46001 : 28. Hence, x = 353 x
27.46001 / 28 = 346.192 cubical inches, which is the volume the same
quantity of air would have occupied at 28 inches of the barometer.

The 210th part of this corrected volume is 1.65, which, for the five
degrees of temperature above the standard gives 8.255 cubical inches;
and, as this correction is subtractive, the real corrected volume of the
air before combustion is 337.942 inches.

_Calculation after Combustion._

By a similar calculation upon the volume of air after combustion, we
find its barometrical pressure 27.77083 - 0.51593 = 27.25490. Hence, to
have the volume of air under the pressure of 28 inches, 295 : x ::
27.77083 : 28 inversely; or, x = 295 x 27.25490 / 28 = 287.150. The
210th part of this corrected volume is 1.368, which, multiplied by 6
degrees of thermometrical difference, gives the subtractive correction
for temperature 8.208, leaving the actual corrected volume of air after
combustion 278.942 inches.

_Result._

The corrected volume before combustion 337.942

Ditto remaining after combustion 278.942
--------
Volume absorbed during combustion 59.000.

SECT. VIII.

_Method of determining the Absolute Gravity of the different Gasses._

Take a large balloon A, Pl. V. Fig. 10. capable of holding 17 or 18
pints, or about half a cubical foot, having the brass cap bcde
strongly cemented to its neck, and to which the tube and stop-cock f g
is fixed by a tight screw. This apparatus is connected by the double
screw represented separately at Fig. 12. to the jar BCD, Fig. 10. which
must be some pints la