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III. 



NOTE ON AZEOTEOPIG MIXTURES. 



By PROFESSOR SYDNEY YOUNG, D.Sc, F.R.S., 

 Trinity College, Dublin. 



[Read Novemher 13. Published December 22, 1922.] 



More than sixty years ago Roscoe found that a certain mixture of hydro- 

 chloric acid and water distilled, without change of composition, at a constant 

 temperature higher than the boiling point of either component. He showed 

 that the composition of the mixture of constant boiling point varied with the 

 pressure under which the distillation was carried out. Roscoe afterwards 

 obtained similar results with a number of other acids. 



Shortly afterwards Berthelot noticed that a particular mixture of ethyl 

 alcohol and carbon disulphide boiled at a constant temperature lower than 

 the boiling point of either pure substance ; and Chancel observed that propyl 

 alcohol and water formed a mixture of minimum boiling point. 



Since then a very large number of binary mixtures of minimum boiling 

 point and a much smaller number of mixtures of maximum boiling point 

 have been discovered, notably in recent years by Lecat.^ 



The term " azeotropic mixtures " was proposed by Wade and Merriman,* 

 and adopted by Lecat for mixtures of constant boiling point. 



Benzene and ethyl alcohol and ethyl alcohol and water respectively 

 form mixtures of minimum boiling point, whilst benzene and water are 

 practically non-miscible ; and it was observed by the author in 1902 that 

 when any mixture of the three liquids is distilled through a very efficient 

 still-head, a ternary azeotropic- mixture of constant composition comes over 

 at a temperature lower than the boiling point of any one of the three binary 

 mixtures or of any of the single substances. 



Ternary azeotropic mixtures of several of the lower alcohols of the ethyl 

 alcohol series with benzene and water and with w-hexane and water were 



■ " La Tension de Vapeur des Melanges de Liquides ; L'Az^otropisme," Brusaels, 1918, 

 2 Trans. Chem. Soc, 1911, 99, 1004. 



