962 



SCIENCE 



[N. S. Vol. XXV. No. 651 



SCIENTIFIC BOOKS 



Hydrates in Aqueous Solution. Evidence for 

 the existence of hydrates in solution, their 

 approximate composition, and certain spec- 

 troscopic investigations bearing upon the 

 hydrate problem. By Harry C. Jones, with 

 the assistance of F. H. Getman, H. P. Bas- 

 SETT, L. McMaster and H. S. TJhler. Pp. 

 viii ■+ 264. Publication No. 60 of the Car- 

 negie Institution, Washington, D. C, 1907. 

 The first part of this monograph, covering 

 157 pages, presents the detailed results of 

 earlier work and the measurements of Getman 

 and Eassett of freezing-points, electrical con- 

 ductivity, specific gravity and refractive power 

 of solutions. All the observations were made 

 on aqueous solutions, except a series of deter- 

 minations made by McMaster, presented on 

 pages 149 to 152, which relate to solutions of 

 lithium chloride, bromide and nitrate in 

 methyl and ethyl alcohol and to calcium 

 nitrate in the latter solvent. In the case of 

 the aqueous solutions, 98 compounds, inclu- 

 ding acids, salts and bases were studied; and 

 in the course of this work between 1,400 and 

 1,500 solutions were examined. The purpose 

 of making the specific gravity determinations 

 was merely to permit a computation of the 

 lowering of the freezing-point per 1,000 grama 

 of solvent, the solutions having been prepared 

 by .dissolving a certain weight of substance in 

 water and then diluting to a definite volume. 

 The refractive indexes when charted as 

 ordinates against the concentration of the 

 solutions as abscissas yield curves which are 

 practically straight lines in all cases. They 

 consequently bear no simple relation to either 

 the conductivity or freezing-point curves, and 

 are, indeed, not used later in the argument 

 concerning hydrates in solution. 



The electrical conductivities of the solu- 

 tions were measured for the purpose of ascer- 

 taining the so-called degree of electrolytic dis- 

 sociation of the dissolved substances. When 

 the molecular conductivities are charted as 

 ordinates and the corresponding volumes as 

 abscissas, smooth curves are obtained in all 

 cases. These curves have in general a simi- 

 lar trend, being concave toward the axis of 



abscissas for the various electrolytes investi- 

 gated. 



The ebullioseopic method was employed in 

 but few of the aqueous solutions; the alco- 

 holic solutions were, of course, investigated by 

 this method. On the other hand, the cryo- 

 scopie method was very extensively employed 

 in studying the aqueous solutions, and in order 

 to make comparison possible, the electrical 

 conductivity measurements were made at 0° C. 

 When the molecular lowerings of the freezing- 

 point are charted as ordinates and the mole- 

 cular concentrations as abscissas, curves are 

 obtained which are in general convex toward 

 the axis of abscissas. In some cases the 

 points of inflexion are quite well defined, in 

 other cases the curves are fairly flat, and in 

 still others they are nearly straight lines. In 

 the few cases where boiling-point curves have 

 been similarly charted, these show the same 

 general behavior, except that the points of 

 inflexion occur at a greater concentration 

 than in the freezing-point curves. 



The chief argument presented in the mono- 

 graph for the existence of hydrates in solution 

 is the occurrence of minima in these freezing- 

 point and boiling-point curves. From the fact 

 that the minima occur at higher concentra- 

 tions in the boiling-point curves, it is argued 

 that the hydrates are less stable at higher 

 temperatures and hence require gTeater con- 

 centration for their formation than at lower 

 temperatures. To be sure a point is also made 

 of a supposed relation between lowering of 

 the freezing-point and water of crystallization 

 of the dissolved substance, it being claimed 

 that high crystal water content and a large 

 depression of the freezing-point go together. 

 As a matter of fact, however, the behavior of 

 solutions of many salts rich in crystal water 

 speaks strongly against this supposed relation. 

 So for instance, the sulphates in general give 

 relatively small lowerings of the freezing- 

 point, a fact which, moreover, is not new. 

 This behavior of the sulphates it is stated is 

 ' abnormal ' and due to polymerization of the 

 salts.' However, no independent evidence is 

 adduced to support the assumption that such 

 polymerization occiirs, and so the relation 

 which it is claimed exists between lowering of 



