(6) Vs = v(p - a)/(760(1 + 0.00366t)).
The following problem will serve to illustrate the method of applying the correction for the pressure of the aqueous vapor.
The volume of a gas measured over water in a laboratory where the temperature is 20° and the barometric reading is 740 mm. is 500 cc. What volume would this occupy under standard conditions?
The pressure exerted by the aqueous vapor at 20° (see table in Appendix) is equal to the pressure exerted by a column of mercury 17.4 mm. in height. Substituting the values of v, t, p, and a in formula (6), we have
(6) Vs = 500(740 - 17.4)/(760(1 + 0.00366 × 20)) = 442.9 cc.
Adjustment of tubes before reading gas volumes. In measuring the volumes of gases collected in graduated tubes or other receivers, over a liquid as illustrated in Fig. 8, the reading should be taken after raising or lowering the tube containing the gas until the level of the liquid inside and outside the tube is the same; for it is only under these conditions that the upward pressure within the tube is the same as the atmospheric pressure.
EXERCISES
1. What is the meaning of the following words? phlogiston, ozone, phosphorus. (Consult dictionary.)
2. Can combustion take place without the emission of light?
3. Is the evolution of light always produced by combustion?