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XXXII. The Densities of Solutions of Soda and Potash. 

 By Spencer Umfreville Pickering, F.R.S.* 



IT is somewhat remarkable that there exist no modern or 

 exact determinations of the densities of solutions of soda 

 or potash. Berthelot, it is true, made series of observations 

 with both substances, but his results have no pretensions to 

 accuracy, the values being given to the third decimal place 

 only, and applying to temperatures varying from 10° to 15°. 

 The tables which are generally reproduced in text-books, as 

 well as in the works of Schiff and of Gerlach on densities, 

 are those which Tunnermann constructed as far back as 1827. 

 These tables are based on half a dozen determinations at most, 

 and on a theory which can scarcely be accepted at the present 

 day ; they are fairly voluminous, and as Tunnermann calcu- 

 lated the values for percentage strengths not expressed by 

 round numbers, they seem to have been generally accepted as 

 experimental instead of calculated values. They show errors 

 extending up to a unit in the second decimal place, and when 

 plotted out give figures bearing very little resemblance to 

 the true ones. Dalton also made some determinations 

 ('Elements/ ii. p. 315 |)> and possibly also Bichter (Stochio- 

 metrie, iii. p. 332 f ), but as I have failed in procuring his 

 work (or Dalton's either) I am uncertain whether they were 

 original determinations or not. In any case determinations 

 of such a date could only be roughly approximate. 



Apart from the desirability for practical purposes of 

 having accurate tables of the densities of such familiar sub- 

 stances as soda and potash, there were questions of theoretical 

 importance which induced me to investigate their solutions. 

 My work on Sulphuric Acid (Chem. Soc. Trans. 1890, pp. 61, 

 331) had indicated the existence of numerous hydrates in 

 solution, but beyond the indications afforded by the changes 

 of curvature themselves there was very little independent 

 evidence as to the particular hydrates indicated, one only 

 had been known to exist in the solid condition, and one other 

 was subsequently isolated. But in the case of soda, my recent 

 work (Chem. Soc. Trans. 1893, p. 890) has shown that the 

 hydrates which can be crystallized from moderately strong 



* Communicated by the Author. 



f These references are taken from Watts's ' Dictionary of Chemistry,' 

 v. p. 339. 



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