Vapour pressure ratio

The efficiency of a distillation apparatus used for purification of liquids depends on the difference in boiling points of the pure material and its impurities. For example, if two components of an ideal mixture have vapour pressures in the ratio 2 1, it would be necessary to have a still with an efficiency of at least seven plates (giving an enrichment of 2 = 128) if the concentration of the higher-boiling component in the distillate was to be reduced to less than 1% of its initial value. For a vapour pressure ratio of 5 1, three plates would achieve as much separation. 

The vapour pressure ratio of actinides to noble metals is also the basis of the actinide metal preparation by thermal dissociation of intermetallic compounds. Such intermetallic compounds of An and noble metals can be prepared by hydrogen reduction of a mixture of an An oxide and a finely divided noble metal (Pt, Ir.. in the absence of noble metals, hydrogen reduction of An oxides is impossible. Am and Cm metals have been obtained by thermal dissociation of their intermetallic compounds with Pt and Ir High purity Th and Pa, the least volatile actinide metals, can be prepared by thermal dissociation of their iodides, which form readily by reaction of iodine vapour with car-... 

Ow—the activity of water, i.e. vapour pressure ratio of the water in the mixture to that of pure water ... 

According to Urey [57], can be expressed in terms of the vapour pressure ratio of the two components as... 

Vapour pressure ratio of the system against temperature... 

An azeotrope with minimum boiling point is formed if the activity coefficient of the high-boiling component is greater than the vapour pressure ratio of the pvure coiiiponents. 

The operation described provides, then, an alternative method of reversible dilution. The maximum work obtainable by the first method is expressible in terms of the osmotic pressure that obtainable by the second method is expressible in terms of the vapour-pressure ratio. These two quantities of work, as is easily shown, must he equal, provided that temperature is constant. 

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