528 Lord Rayleigh on the 



of f in the ratio of 2 11 : 1. The residue in the retort thus 

 approximates rapidly to pure water. 



On the other hand, in the case or! acetic acid and water 

 k is about f . When weak acetic acid is distilled the residue 

 strengthens, but the earlier stages of the process are covered 

 by the formula given, which now assumes the form 



In order to double the strength of the liquid remaining in 

 the retort, 15/16 of it would have to be distilled away, or 

 again, in order to increase the stiength in the ratio of 3:2, 

 the distillation must proceed until the liquid is reduced in 

 the ratio of 16 : 81, or nearly of 1:5. An experiment of 

 this sort upon acetic acid is recorded below. 



Observations. 



The experimental results about to be given were obtained 

 by simple distillation of mixtures of known composition. In 

 order to avoid too rapid a change of coir, position, somewhat 

 large quantities were charged into a retort and were kept in 

 vigorous ebullition. By special jacketing arrangements 

 security was taken that the upper part of the retort should 

 be maintained at a distinctly higher temperature than the 

 liquid, so that there could be no premature condensation 

 which would vitiate the result. All the vapour rising from 

 the liquid must be condensed in the specially provided Liebig 

 condenser and be collected as distillate. Subject to this 

 condition, and in view of the rapid stirring effected by the 

 rising vapour, it would seem safe to assume that the distillate 

 really represents the vapour which is in equilibrium with the 

 liquid at the time in question. The compositions of the liquid 

 and vapour are of course continually changing as the dis- 

 tillation proceeds. 



The distillates (including the first drop) were collected in 

 50 c.c. measuring flasks. It will save circumlocution to 

 speak of a particular case, and I will take that of alcohol and 

 water, for which the analyses were made by specific gravity. 

 The successive collections of 50 c.c. show an increasing 

 specific gravity corresponding to a diminishing strength. 

 The specific gravity of each gives the total weight, and the 

 strength, deduced from tables, allows us to calculate the 

 alcohol and water in each collection. The total alcohol and 

 water originally present in the retort being known in the 

 same way, we are able to deduce by subtraction the quantities 

 remaining in the retort at each stage, and thus to compare 

 the strengths of corresponding liquid and vapour. In the 



