TRANSACTIONS OF SECTION B. 675 



Besides the increased data thus obtained, fresh light has been thrown on 

 (I) The physical question at the basis of the inquiry. Additional proofs have 

 been given that specific refraction is constant (or nearly so) notwithstanding 

 ■solution or change from the gaseous to the liquid or solid condition. (2) The 

 refraction equivalents of the elementary bodies. A revision of the old list (' Phil. 

 Trans.' 1869) in the light of our present knowledge has led to the results embodied 

 in the table given above. Many of the figures will doubtless require future modi- 

 fication. (3) The chemical structure of many compounds, especially among organic 

 bodies rich in carbon. Some of these deductions have already become the subject 

 of controversy in the scientific journals of the Continent. 



•5. On the Diffusion of Metals. By Professor W. Chandler Roberts, F.R.S. 



6. On some Phenomena of Solution illustrated by the case of Sodium 

 Sulphate. By Professor William A. Tilden, D.Sc., F.R.S. 



From a study of the solubility of sodium sulphate in water at temperatures 

 above 100° C, the author (in conjunction with Mr. Shenstone) has arrived at 

 the conclusion that at these high temperatures the salt dissolves in the anhydrous 

 .state. In order to determine whether this salt dissolves in water at lower 

 temperatures in the anhydrous or in the hydrated state he has made a series of 

 calorimetric measurements of the thermal changes which attend the act of solution 

 of Na,S0 4 in water at temperatures below and above 33°-84°, the critical point in 

 the curve of solubility. The following are the chief results : 



Calorimetric effect, C, of dissolving Na 2 S0 4 in n molecules of water at t°, 

 n. t° C. 



100 31-70 1740 



100 35-40 1522 



100 42-85 1342 



100 46-10 1071 



100 55-00 985 



These figures establish the fact that by dissolving anhydrous sulphate of sodium 

 in water at temperatures above 33°-34° the thermal change is still positive, 

 although a diminishing quantity, and hence that the act of solution is still attended 

 at these temperatures by chemical combination between the salt and a portion of 

 the water. These results when plotted out give a line which is nearly parallel 

 with the solubility curve between these limits of temperature. 



7. A Theory of Solution. By W. W. J. ISTicol, M.A., B.Sc. 



This paper contained a resume of the experimental evidence accumulated by 

 the author in support of his theory, a complete enunciation of which was given in 

 a paper read before the Boyal Society of Edinburgh in January 1883, and pub- 

 lished in the ' Philosophical Magazine ' for February of the same year. 



8. On Evaporation and, Dissociation. 

 By Professor William Ramsay, Ph.D. and Sydney Young, D.Sc. 



The authors described experiments made with the object of ascertaining whether 

 the coincidence of the curves which represent the vapour pressures of stable solid 

 and liquid substances at different temperatures with those indicating the maximum 

 temperatures attainable by the same substances at different pressures, when 

 •evaporating with a free surface, holds good also for substances which dissociate in 

 their passage to the gaseous state._ The substances examined were chloral hydrate, 

 ammonium carbonate, phthalic acid, succinic acid, aldehyde ammonia, ammonium 

 chloride, nitric peroxide, and acetic acid. It was found that with chloral hydrate 



x x 2 



