from that of atmospheric air. Hence I may take for granted, till farther
experiments give us better information upon this subject, that
atmospherical air is dilated 1/210 part, and hydrogen gas 1/190 part for
each degree of the thermometer; but, as there is still great uncertainty
upon this point, we ought always to operate in a temperature as near as
possible to the standard of 10 , (54.5 ) by this means any errors in
correcting the weight or volume of gasses by reducing them to the common
standard, will become of little moment.
The calculation for this correction is extremely easy. Divide the
observed volume of air by 210, and multiply the quotient by the degrees
of temperature above or below 10 (54.5 ). This correction is negative
when the actual temperature is above the standard, and positive when
below. By the use of logarithmical tables this calculation is much
facilitated[59].
SECT. VII.
_Example for calculating the Corrections relative to the Variations of
Pressure and Temperature._
CASE.
In the jar A, Pl. IV. Fig. 3. standing in a water apparatus, is
contained 353 cubical inches of air; the surface of the water within the
jar at EF is 4-1/2 inches above the water in the cistern, the barometer
is at 27 inches 9-1/2 lines, and the thermometer at 15 (65.75 ). Having
burnt a quantity of phosphorus in the air, by which concrete phosphoric
acid is produced, the air after the combustion occupies 295 cubical
inches, the water within the jar stands 7 inches above that in the
cistern, the barometer is at 27 inches 9-1/4 lines, and the thermometer
at 16 (68 ). It is required from these data to determine the actual
volume of air before and after combustion, and the quantity absorbed
during the process.
_Calculation before Combustion._
228