151 



Boiling and Condensing Points of Alcohol Water 



Mixtures. 



p. N. Evans. 



The boiling points of mixtures of alcohol and water depend on the pro- 

 portions of the constituents and range from about 70° C. for pure ethyl alcohol 

 to 100° C. for ])ure water. Except at a concentration of about 92 per cent, 

 alcohol by weight (about 96 per cent, by volume) any mixture of alcohol and 

 water when boileil gives off a vapor of different comjjosition from the liquid, 

 the vapor being richer or pooi'er in alcohol than the lifjuid when the latter 

 contains respectively less or more than 92 per cent, of alcohol. The vapor 

 has, of course, a condensing point identical with the true boiling point of the 

 liciuid from which it is given off. 



The purpose of the w'ork here reported was to ascertain experimentally 

 the relation between the boiling point (or condensing point) and the compo- 

 sition of both the liciuid and vapor phases, so that with the information so 

 obtained it would be possible by observation of the corrected boiling point 

 to learn the composition of the boiling licjuid and of the condensing vapor. 



PROCEDURE. 



The gravity and temperature of a strong alcohol were determined with 

 a Westphal balance, and the weight-per cent, of alcohol calculated by means 

 of Mendelejeff's table. P'ive himdred cubic centimeters were placed in a 

 one-liter distilling flask with an accvirate thermometer graduated in tenths 

 of a degree placed with its bulb just below the side-neck. The liquid was 

 then slowly distilled at a uniform rate of about one drop per second until 

 15 c. c. had passed over, the distilling temperature being read when 7.5 c. c. 

 had collected in the graduated receiver. The per cent, of alcohol in the dis- 

 tillate and in the residue was determined from the gravity as before. 



The average of the percentages found in the liciuid in the flask before 

 and after distillation was taken as that of the liquid phase, and the percentage 

 in the distillate as representing the vapor phase at a moment half-way througli 

 the distillation when the boiling ]:)oint was observed. 



