NATURE 



93 



THURSDAY, DECEMBER 31, 1891. 



THE PHYSICAL THEORY OF SOLUTION. 

 Solutions. By W. Ostwald. Translated by M. M. 

 Pattison Muir. Pp. 316. (London : Longmans, Green, 

 and Co., 1891). 



WITH certain additions this work is a translation of 

 Book IV. of the second edition of Ostwald's 

 " Lehrbuch der allgemeinen Chemie." At the present 

 time there is no department of physical chemistry which 

 is receiving more attention, and which is the subject of 

 more controversy, than that of solutions. On the Con- 

 tinent, the physical theory of solution, arising out of the 

 ideas of van 't Hofif and Arrhenius, has obtained, for the 

 most part, ready acceptance. Although the earlier of 

 these conceptions is but some six years old, their ap- 

 plications and the facts accumulated around them have 

 already become so numerous that to piece fact and theory 

 together, and keep the main issues of the case to the fore, 

 is a necessity. To carry out these ends no one is better 

 fitted than the Professor of Chemistry in the University 

 of Leipzig. Prof. Ostwald is one of the warmest sup- 

 porters of the physical theory, and has done more, 

 perhaps, than any other, to make it what it now is. 



As contrasted with its reception on the Continent, the 

 new theory has had but little favour shown to it in this 

 country. Men of science on this side of the Channel 

 have, as a rule, been unwilling to grant the more startling 

 consequences which follow in its wake, and have offered 

 more or less decided opposition to its progress. Of late, 

 too, the claims of a special development of the rival 

 hydrate or chemical theory have been brought prominently 

 under their notice. There is therefore a certain fitness in 

 the publication of a " full and authoritative statement " in 

 English of the merits of the physical theory. 



The book opens with a definition of solutions. In the 

 light of the physical theory these are "homogeneous 

 mixtures which cannot be separated into their constituent 

 parts by mechanical means." Granting this definition, it 

 forms a basis for classifying the different kinds of solu- 

 tions, and these, together with the conditions under which 

 they are formed, and under which they exist, are discussed 

 in the first four chapters. 



Chapter i., solutions in gases, begins with an account 

 of Dalton's law of partial pressures, and the deviations 

 from the law brought to light by the work of Regnault, 

 Andrews, and others. The somewhat novel result that 

 this gaseous law should be found under the heading 

 solutions, follows, of course, from the fact that a gaseous 

 mixture satisfies the definition quoted. The rest of the 

 chapter is taken up with the evaporation of liquids and 

 solids, as these processes may be regarded as instances of 

 the solution of liquids and of solids in gases. 



Solutions in liquids are considered in the next three 

 chapters. Chapter ii. is devoted to solutions of gases 

 in liquids. Henry's law, its verification by Bunsen, the 

 methods of determining absorption coefficients, and the 

 exceptions to Henry's law shown by aqueous solutions of 

 ammonia, hydrogen chloride, &c., are given first. Then 

 follow sections on the theory of gas-absorption, on ab- 

 sorption by saline solutions and by mixed liquids, and on 

 NO. I 157, VOL. 45] 



the volume changes of liquids accompanying absorption. 

 Chapter iii. deals with mixed liquids, classified according 

 as they are miscible in all proportions, partially miscible, 

 or practically immiscible. Alexejeff's interesting curves 

 representing the mutual solubility of different pairs of 

 liquids at different temperatures here find a place. The 

 observations of Konowaloff on the vapour pressures of 

 mixed liquids are described at some length, and are worthy 

 of attention, in particular those relating to liquids miscible 

 in all proportions, as they are of especial value in the 

 process of fractional distillation. 



Chapter viii. of Book V. of the " Lehrbuch," solutions 

 of solids in liquids, is now introduced. That it is not 

 quite continuous with its predecessors is apparent by the 

 abrupt mention of osmotic pressure, and the use of van 't 

 Hoff 's factor z, reference being made by the translator to 

 succeeding chapters for explanations. Free application 

 of the gaseous laws to solutions is made in this chapter, 

 which treats of supersaturation, the influence of ex- 

 ternal pressure and of temperature on solubility, the 

 volume relations of solutions, the influence of melting on 

 solubility, the solubilities of mixtures, the effect of acids 

 on the solubilities of their salts, solutions in mixed 

 liquids, &c. The emphasis laid on the fact that in a 

 saturated solution in contact with undissolved substance, 

 the latter plays an important part in the conditions 

 of equilibrium, is noteworthy. 



Under osmose, is next given an account of osmotic 

 pressure, and of the work of Traube, Pfeffer, de Vries,. 

 and others, with the theoretical deductions of van 't Hoff 

 which were founded on such researches, and which re- 

 sulted in quantitative support to the idea of the analogy 

 between solutions and gases. This chapter might with 

 profit have been given at an earlier stage, at least before 

 the previous one, on the solution of solids in liquids. 



The chapter ;following, on the diffusion of dissolved 

 substances, contains a valuable abstract of the main in- 

 vestigations on this subject, from the time of Graham 

 down to the present, when Kick's fundamental law of 

 diffusion follows, as shown by Nernst, from consideration 

 of the effect of osmotic pressure. 



Chapters vii. and viii. treat respectively of the vapour 

 pressures and freezing-points of solutions. A full and 

 historical account, with the practical applications to 

 molecular weight estimations, is given in each case. Salt 

 solutions are next discussed, the leading idea of the 

 chapter being to prove that the properties of electrolytes 

 are additive, or can be expressed as the sum of the 

 properties of their constituent ions. Both chemical and 

 physical properties are quoted in support of the existence 

 of free ions in salt solutions. The last chapter is devoted 

 to the simultaneous action of different solvents. The use 

 of some of the results as new methods of determining 

 molecular weights is also indicated. 



On the whole, the book is a very suggestive one. The 

 historical method adopted in each chapter adds much to 

 the interest. The arrangement of the facts concerning 

 solutions, and the copious references to original memoirs, 

 are alone sufficient to make the book valuable ; and to 

 many, those chapters, such as that on diffusion, which deal 

 mainly with fact, will be the most useful. Even although,, 

 in the investigation of solution, the use of the gaseous 

 laws be nothing more than the carrying out of a mere 



K 



