Phial filler for large volumes

A generally useful method of metering small quantities of compounds with reasonable vapour pressures is to condense the vapour of the compound from a known volume at a known temperature. If the vapour of a liquid or a solid in a reservoir A can expand into an evacuated bulb B of volume V (see Fig. 3.11), then the number n of moles in V is given to an adequate degree of accuracy by the Ideal Gas Law pV = nRT where p is the vapour pressure of the compound at a temperature T which must be lower than the ambient temperature of the vapour (Biddulph and Plesch, 1959). 

The measurements can be done in two ways, according to circumstances. If the quantity of compound to be measured out is between ca. 0.05 and 0.5 g, the contents of the bulb B of (approximately) known volume can be 

For metering very small quantities, the volume of the bulb must be known accurately. The amount of material in it can be controlled very closely by changing the temperature of the compound in the reservoir, provided that its vapour pressure curve is known. By using the vapour of ice, it was possible to measure out ca. 10 mole of water (ca. 2 x 10 g), (Biddulph, Plesch and Rutherford, 1965). 

It is evident that the vapour method cannot be used with compounds which dissociate appreciably at ambient temperatures, e.g. PCI5 and SbClj. 

If fixed quantities of a compound are required frequently, as when the rate of a reaction is studied as a function of a concentration, it is convenient 

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