PEESIDBNTIAL ADDKESS — SECTION B. 99 



is hardly necessary to say that this equality of the two 

 ingredients is an accident which does not characterize all 

 cases. 



Now, imagine a 50-per-ceut. mixture of aniline and water 

 sealed up in a tube, shaken, and gradually heated. Let us 

 assume that the tube is only large enough to hold the mixture 

 and allow of expansion by heat, so that evaporation may be 

 neglected as too small to materially complicate the result. 

 The course of events will be exactly what I have described 

 with reference to the hypothetical A layer and B layer. There 

 will be formed a saturated solution of water in aniline, which 

 we may call the aniline layer, and a saturated solution of 

 aniline in water — the ivater layer. Given the temperature, 

 the percentage strength of each layer may be read off from the 

 curve. As the temperature rises the two layers will effect 

 exchanges in such a way that the aniline layer will become 

 poorer, and the water layer richer, in aniline ; and at about 

 167° the two layers will have attained equal strength and 

 become merged into one. Were we to start with the aniline 

 and water in any other proportions by weight, there would 

 still be formed the two saturated solutions, but their relative 

 amounts would be different, and one or other would be used 

 up and disappear at a lower temperature. To attain the 

 maximum temperature of complete solution you must start 

 with the exact proportions which correspond to that tempera- 

 ture. 



But it is possible to learn even more from Alexeeff's work 

 than he himself has made evident. Let me call your attention 

 to the curve shown in Fig. 2,''' PI. IV., the data for which I 

 have calculated in the following manner : From Alexeeff's 

 percentage-figures was deduced the weight of water capable 

 of dissolving, or being dissolved by, one gramme of aniline at 

 each of his experimental temperatures, so as to form a satu- 

 rated solution. Then, from curves showing the expansion of 

 pure water and pure aniline (the latter drawn from Thorpe's 

 data — Trans. Cheni. Soc, 1880), there were read the specific 

 volumes of these substances at each of Alexeeff's temperatures ; 

 and from the combined information thus obtained there was 

 calculated the total volume of that quantity of the saturated 

 solution at each temperature which contains one gramme of 

 aniline. This is what I have already called the specific solu- 

 tion-volume. A slight error is involved by the fact that the 

 volume of a solution is not exactly the sum of the volumes of 

 its ingredients ; but this error is necessarily small — too small 



* In order to save space, only the upper portion of the curve is here 

 represented, as it shows all that is essential to the argument. Of the 

 twelve experimental points, one appears to be somewhat misplaced ; but 

 this does not affect that part of the curve which is shown in the figure. 



