The Nature of Solutions. 427 



molecular and chemical differences in isomeric liquids. It 

 may be used to detect and measure the changes gradually 

 produced by light and heat in chlorine water and bromine 

 water, the influence of light upon nitric acid, the degrees of 

 retarding effect of coloured glass screens &c. upon various 

 chemical changes caused by light, the gradual oxidation of a 

 solution of sulphurous anhydride by exposure to air, the 

 spontaneous decomposition of aqua regia, the rate of de- 

 composition of a solution of potassic iodide by chlorine water, 

 the speed of displacement of one acid by another, &c, &c. 

 The examples given and researches suggested are sufficient 

 to indicate the very great extent of the subject. 



XLV . The Nature of Solutions. 

 By Spencer Umfreville Pickering, M.A* 



IN the March number of the Journal of the Chemical 

 Society there was published a paper by the present writer, 

 " On the Nature of Solutions," which had been honoured by 

 an adverse criticism from Prof. Arrhenius (Phil. Mag. 1889, 

 xxviii. p. 36) eight months before its appearance in extenso. 



It is impossible to answer the objections raised by Prof. 

 Arrhenius without giving some account of the work itself ; 

 and, as this work is of a character calculated to interest many 

 physicists, it may be advisable to give here a somewhat fuller 

 rfeume' of it than would otherwise be necessary. 



Solutions of sulphuric acid formed the subject of the inves- 

 tigation. Series of density-determinations with solutions of 

 different strengths were made at 8°, 18°, 28°, and 38°, each 

 series consisting of 50 to 100 determinations. A still more 

 elaborate series of determinations of the heat of dissolution at 

 18° were made, as well as some of the heat-capacity of solu- 

 tions up to 12 per cent, in strength. From the density-results 

 at 18° the contraction on mixing was calculated, and these 

 values treated independently. The density-results, moreover, 

 at the four different temperatures gave the means of calcula- 

 ting the expansion by heat for various intervals of temperature ; 

 and, finally, F. and W. Kohlrausch's determinations of the 

 electric conductivity were re-examined, the first examination 

 of them having been made by Crompton (Chem. Soc. Trans. 

 1888, p. 116). 



Different solutions were for the most part used in investi- 

 gating the different properties, and the total number of deter- 

 minations made amounted to 600 or 700. 



The results were examined by plotting them out, and by 

 * Communicated bv the Author. 

 2K2 



