Vapor-density bulb

Figure 1-2 Schematic diagram of a Victor Meyer apparatus for determination of the vapor density of a substance that is volatile at the oven temperature 7V The air displaced from the heated chamber by the volatilization of the sample In the bulb is measured in the gas burette at temperature 72 as the difference in the burette readings V2 and V,.

Vapor density provides a useful means of molecular weight determination for substances which exert a high vapor pressure at or near room temperature. In the simplest case, an evacuated bulb of known volume is tared, filled with a measured pressure of the gas at a known temperature, and is reweighed. These pressure, temperature, and volume data yield the moles of gas (if the ideal gas law is assumed) and the additional weight data permit the calculation of (he number of grams per mole. 

The determination of vapor density is also of considerable value in the determination of molecular weights of low-boiling compounds (under 100°C). Several methods have been used, but the simplest is to prepare a small thin-walled bulb with a capillary tip (Fig. 3-7),... 

A gas sample was collected in an apparatus similar to that in Fig. 5-7 except that the confining liquid was water. At 17 C the volume of gas was 67.3 cm the barometric pressure was 723 torr, and the water level in the bulb was 210 mm below that in the collection tube. Later that day the room warmed to 34 °C and the barometer went up to 741 torr. The experimeter slowly adjusted the bulb to equalize the levels. What was the new volume reading The vapor pressure of water is 14.5 torr at 17"C and 39.9 torr at 34 C. The density of mercury is 13.6 times that of water. 

Antibiotic crystals in a filter cake are placed in trays at a depth of 2.0 cm and dried with excess solvent-free air at 40 °C (dry bulb). The crystals have a wet density of 0.77 g crystal/cm cake and each tray originally contains 8.0 wt% acetone whose vapor concentration c in mol/cm is approximated by the equation... 

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