14 MR J. Y. BUCHANAN ON THE 



SECTION XVI. 



The Determination op the Specific Gravity of the Crystals op a Soluble Salt by Displacement 

 IK its own Mothbb-Liquor, and the Volumetric Relations between the Crystals and the 

 Mother-Liquor which are established by the Experiment. 



PAR. PAGE 



120. This work was undertaken owing to the arrival of the great anticyclone or heat-wave of 202 



the summer of 1904, which made observations of specific gravity at 19 '5° impossible. 

 The liquid in which every soluble salt is quite insoluble is its own mother-liquor at the 

 temperature at M'hich the one parted from the other. It was in this liquid that the 

 specific gravity of the crystals of tlie salts of the two enneads MR and MRO3 was 

 determined. It is obvious that this method is applicable only to salts which have a 

 mother-liquor, such as KCl, RbBr, CaCIgGHgO, BaCl22H20. It is inapplicable to salts 

 such as CaCly, BaClg, and the like, which have no legitimate mother-liquor. The anti- 

 cyclone prevailed throughout the greater part of July and August 1904, during which 

 time the determinations of the specific gravity of the crystals and the mother-liquors 

 of the salts of the ennead MR were determined. 



121. Precautions to be observed in making the experiment. 203 



122. Determinations of the solubility of the salts RbBr, Rbl, CsCl, CsBr and Csl were made, 203 



as there were no published data regarding them. The preliminary experiments are here 

 described. 



123. Contains Table I. in which the experimental data and details are given in full in the case 204 



of one salt, namely, CsCl. All the weights as given represent the weight in vacuo. 

 Further necessary details of the experimental method are here given. 



124. Precautions to be observed when bringing the crystals together with the mother-liquor in 206 



the pyknometer. The experimenter must realise that their common temperature when 

 mixed is to be exactly that of crystallisation or equilibrium, and he must take such 

 measures as his experience dictates to arrive at this end. 



125. Contains Table II., which gives for each salt the temperature, T, of equilibrium between 207 



crystals and mother-liquor, and in condensed form the experimental data of the determina- 

 tion of S, the specific gravity at T of the mother-liquor, that of water at the same 

 temperature being unity ; of m, the concentration of the mother-liquor in gram-mole- 

 cules of salt per 1000 grams of water; and of D^, Dj jDg, the three observed values, as 

 well as D, the finally accepted value of the specific gravity of the salt, all at T, and 

 referred to that of water at the same temperature as unity. 



126. General discussion of the results. 209 



127. Contains Table III., giving numerical relations between the crystallised salts of the ennead 209 



MR and their mother-liquors. 



128. Discussion relative to the mother-liquor. 211 



129. Consideration of saturated solutions as products of substitution. 212 



130. Comparison of the displacement of the salt in crystal and the increment of displacement 213 



of 1000 grams of water which is produced by its dissolution. It is shown that the 

 crystallisation of the potassium and rubidium salts of the ennead must be hindered 

 by increase of pressure, while that of the caesium salts must be helped by the same 

 agency. 



