76 J. G. MACGEEGOE ON THE DENSITY AND THEEMAL, ETC. 



lized salt to a given mass of water, as by adding a mass of anliydrous salt, less than the 

 above mass of crystallized salt by the mass of the w^ater of crystallization, to a mass of 

 water greater than the above by the same amount, it follows that the addition of certain 

 relatively small quantities of anhydrous salt to water must produce a solution with a 

 volume smaller than the volume of the water employed. 



If the differences of the above table are plotted as abscissae, and the percentages of 

 crystallized salt in solution as ordinales, the curve thus obtained shews that the contraction 

 gradually increases with the strength of the solution until it reaches a maximum value in 

 the case of a solution containing 2'1 per cent, of crystallized salt, or about 1*34 per cent, of 

 anhydrous salt, and having, therefore, a density of 1'0151, in which case it amounts to 

 •0048. Hence, an easy calculation shews that if about "0135 gramme of anhydrous salt 

 be added to 1 cubic centimetre of water at 25° C, the volume of the solution will be less 

 than 1 c.c. by about 00485 c.c. 



The curve also shews that as the strength of the solution increases beyond that just 

 mentioned the contraction decreases imtil, for a solution of 74 per cent, of crystallized salt 

 (i.e., 5'96 per cent, of anhydrous salt), it has the value zero. If, therefore, "0632 gramme 

 of anhydrous salt be added to 1 c.c. of water at 25° C, the volume of the solution also will 

 be 1 c.c. For stronger solutions there is no longer a contraction but an expansion. The 

 volume of the solution is greater than the volume of the water it contains. 



These results agree fairly well with those of the approximate direct measurements 

 referred to above, as to the strengths of the solutions shewing maximum contraction and 

 zero contraction respectively. They gaA'e for the former that of a solution containing 

 about 2 per cent, of the anhydi'ous salt, and for the latter that of one containing 5'21 per 

 cent, of anhydrous salt. As to the amount of the maximum contraction, however, the 

 results differ, the direct measurements having given "00048. I am unable to account for 

 this discrepancy. 



Some of the results described above seem to be of sufficient importance to warrant a 

 similar study of other salts. I hope to lay the results of such study before this Society at a 

 future meeting. 



