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XIX. The Molecular Volumes of Salt- Solutions. By W. 
W. J. Nicol, 31. A., B.Sc, F.R.S.E., fyc, Lecturer on 
Chemistry, Mason College, Birmingham *. 
HITHEETO but little attention has been paid to the 
molecular volumes of salt-solutions ; the phrase, so 
far as I am aware, occurs only in the papers of Berthelot, 
Thomsen, and Ostwald. The first of these examined the 
relation of the heat evolved by the solution of the haloid 
acids in water to the molecular volume of the resulting 
solutions f; while Thomsen, in addition to experiments with 
iodic acid similar to those of Berthelot, has pointed out the 
close connexion existing between the molecular heat and 
molecular volume of various salt-solutions J , The experi- 
ments of Ostwald §, quoted by Thomsen (loc. cit.) in support 
of the theory of the " Avidity of Acids," are misleading, as 
the solutions he employed contained two equivalents of the 
salt or acid in every 1000 grms. ; as a consequence, they 
contained different quantities of water, and therefore did not 
really admit of comparison. 
The molecular volume of a solution is a measure of the 
space occupied by the molecules of salt and water forming 
the unit of the solution, along with the intermolecular spaces 
separating them. It is obtained by dividing the molecular 
weight of the unit of the solution by its specific gravity ; or, 
generally, 
^ 1 , xM + nlS 
MoL vol. = k ; 
where M is the molecular weight of the salt, x and n the 
numbers respectively of salt and water molecules, and 5' the 
specific gravity of the solution. 
I hope in the following pages to be able to show that an 
exact and extended knowledge of the molecular volumes of 
salt-solutions will throw much light on the constitution of 
such solutions, and will probably prove a powerful instrument 
in investigating the constitution of the salts themselves. 
With this object in view, I give first the results of the more 
complete and important of my experiments in this direction, 
and shall then proceed to state the conclusions I feel warranted 
in drawing from them. My method of experiment is the 
same as that described in my former paper || ; but, inasmuch as 
* Communicated by the Author. 
f Comptes Hendus, lxxvi. p. 679. 
X Thermocliemische Untersuchungen, Band i. p. 52, ii. p. 427. 
§ Wiedemann's Annalen, ii. p. 429. 
|| Phil. Mag. 1883, xv. p. 91. 
