256 



SCIENCE. 



[Vol. IV., No. 84. 



compounds in relation to their chemical composition, 

 a means for determining molecular weights by optical 

 methods. 



The reports of the committees on spectrum analy- 

 sis and on chemical nomenclature will be published 

 in full, in the annual report of the association. 



A paper was next read on some phenomena of solu- 

 tion illustrated by the cases of sodium sulphate by 

 William A. Tilden. In a recent paper in the Philoso- 

 phical transactions, the author has favored the theory 

 which ascribes solution, not to any combination, 

 chemical or otherwise, of the solid with the solvent, 

 but to liquefaction arising from the mechanical or 

 kinetic action of the molecules of the liquid in which 

 the solid is immersed. This theory is now being 

 tested through a study of the thermal phenomena 

 attending the solution of sodium sulphate. 



Crystallized sodium sulphate containing ten mole- 

 cules of water melts at 33°-34°. At 34° or there- 

 abouts it begins to show signs of dissociation. The 

 maximum point of solubility likewise is at this tem- 

 perature. In consideration of these facts, Professor 

 Tilden propounds the query: In what condition is 

 the dissolved salt at temperatures above 33° ? Is it 

 in the form of the usual hydrate, or is it wholly 

 or in part in the anhydrous state ? The diminished 

 solubility is believed to indicate progressive disso- 

 ciation ; but, this view being questioned, the heat of 

 solutions at temperatures above and below the critical 

 temperature is being determined. The data given, 

 although subject to some slight revision, show that at 

 temperatures as high as 55° the thermal change is 

 still positive, although a diminishing quantity; and 

 hence, that the act of solution is still attended at 

 these temperatures by a chemical combination be- 

 tween the salt and a portion of the water. In this 

 connection, Professor Tilden presented a modified 

 form of calorimeter used in his experiments. 



W. W. J. Nicol next presented a theory of solution. 

 The theory proposed is, that the solution of a salt 

 in water is a consequence of the attraction of the 

 molecules of water for a molecule of salt, exceeding 

 the attraction of the molecules of salt for one an- 

 other. It follows, then, that, as the number of dis- 

 solved salt molecules increases, the attraction of the 

 dissimilar molecules is more and more balanced by 

 the attraction of the similar molecules: when these 

 two forces are in equilibrium, saturation takes place. 

 At the saturation point the force tending to keep in 

 solution any single molecule of salt (attraction of 

 dissimilar molecules) is balanced by the force tend- 

 ing to produce separation of that molecule from the 

 solution (attraction of similar molecules). Further, 

 any external cause tending to alter the intensity of 

 either of these two forces, or to modify both in un- 

 equal degrees, disturbs the condition of equilibrium, 

 and further solution or solidification ensues. The 

 above theory is based on the molecular theory of 

 liquids, and has many points in common with that 

 of Dassios proposed in 1866. 



In putting this theory to the test of experiment, 

 certain results followed which in such a brief note as 

 this cannot be mentioned. 



Mr. Nicol lays stress upon the fact that he expresses 

 the value of a salt solution by n molecules (equiva- 

 lents) of salt to one hundred molecules of water; and 

 he holds that the experiments made on the continent 

 are valueless where they have been made by dissolv- 

 ing one, two, or more molecules of salt in a litre of 

 solution, since, as the molecular volumes of the salts 

 in solution vary, the solutions are not similar as sup- 

 posed. 



A paper followed on evaporation and dissociation, 

 by Professor William Eamsay, and Sydney Young. 

 It having been suggested, that the closer proximity 

 of molecules in the liquid and solid state may be due 

 to the coalescing of two or more gaseous molecules,, 

 to form a complex molecule, the authors hold that 

 the work done in dissociating these complex mole- 

 cules into single molecules is analogous to that ex- 

 pended in converting a solid or liquid into gas, and 

 that the same relations between the existing temper- 

 ature and pressure would exist. The temperature of 

 volatilization of a large number of solids was deter- 

 mined by the ' cage ' described by them before the 

 Koyal society, April, 1884. With bodies like phthalic 

 and succinic acids, this relation was found to exist;, 

 but with acetic acid little or no dissociation was dis- 

 covered. Also a distinct difference was observed in 

 the behavior of dissociating substances in the liquid 

 and solid states when evaporating from a full surface.. 

 So long as a substance is solid, the residue retains its 

 original composition, but a liquid separates into its 

 components: this amounts to a proof that a solid in 

 volatilizing does not pass through the liquid state, 

 and that so long as a substance remains solid it can- 

 not dissociate. The results obtained lead the authors 

 to provisionally doubt the existence of complex mo- 

 lecular groups in liquids. 



The object sought in Professor William Kamsay's 

 paper on molecular volumes was to ascertain whether 

 the boiling-points of compounds, under equal press- 

 ures, really afford suitable points for a comparison of 

 the molecular volumes. The experiments made 

 decisively show that in methyl, ethyl, propyl, iso- 

 propyl, and isobutyl alcohols, and ether, the value of 

 the group CH 2 is by no means constant: while at the 

 boiling-points of the liquids at low pressures, the 

 value is approximately constant, fluctuating between 

 17.5 and 22, at high temperatures the difference 

 becomes much more apparent, attaining at pressures 

 of 20,000 mm. (which was the highest measured) the 

 greatest irregularity. 



Professors Goodwin and Marshall are studying the 

 solubility of chlorine gas in solutions of metallic chlo- 

 rides ; and finding that other experimenters have been 

 observing the expansion of solutions made by dissolv- 

 ing n molecules of the salt in m molecules of water, 

 and that consequently these contain, when diluted, 

 neither the same number of molecules of the salt nor 

 of the water, they have arranged their experiments 

 so that this ratio shall remain constant throughout 

 the observations. 



Sir H. E. Roscoe, speaking in regard to the dia- 

 mantiferous deposits of South Africa and the ash of 

 the diamond, showed that silica and iron oxide form 



