142 Prof. H. L. Callendar aucl Mr. H. T. Barnes. 



The first column contains the percentage by weight, p, of ZnSOi 

 in grams per 100 grams of solution, as deduced from the observa- 

 tions on each solution. The second column contains the values of 

 the density, d, at 20° C, obtained by weighing a special form of 

 pipette carefully filled with the solution. The third column gives 

 w, the weight of ZnS0 4 in grams per cubic centimetre of solution, 

 and is obtained by dividing the product of the numbers in the first 

 two columns by 100. If we add to this weights, the number 0*9982, 

 representing the weight of water in grams per c.c. at 20° C, and 

 subtract the observed density, d, of the solution, we obtain as the 

 difference given in the fourth column, the weight of water displaced 

 per c.c. by the zinc sulphate in solution. 



The observations of Lannoy reduced on a similar plan are as 

 follows : — 





(d) at 15° C. 



pdjlW. 



Difference 

 09992 + w-d. 



Calculated. 



2-25 



1 '0226 



0-0230 



-0-0004 



-oooo 



5-60 



1 -0596 



0-0594 



-o-ooio 



o -oooo 



11 21 



1 '1238 



-1250 



+ 0-0004 



o -oooo 



16-85 



1 -19-19 



0-2013 



+ 0-0056 



+ 0-0057 



These observations, taken in conjunction with our own, would 

 appear to indicate a simple relation between the density and the 

 •composition, of a kind which so far as we are aware has not been pre- 

 viously observed. Up to a density of about 1*150, the solution of 

 zinc sulphate appears to take place approximately without change of 

 volume. The added molecules of ZnS0 4 do not appear to displace 

 any of the molecules of water, so that the density at 20° C. is very 

 nearly 0*9982 + w. Beyond this point, it appears that each added 

 molecule of ZnS0 4 displaces one molecule of water, so that the 

 density of the solution is very approximately represented by the 

 expression 



d = 0-9982 + «'-18(«?-0-150)/161 (D). 



The nature of this relation is perhaps more clearly shown by the 

 curves given in fig. 3. In this figure, the values of to are taken as 

 abscissae, and the corresponding values of the difference 0*9982 + 

 iv — d, as ordinates. The sharp break which occurs at the point 

 w == 0*150 is very clearly shown both by the observations of Lannoy, 

 which are represented by crosses, and by our own which are 

 represented by the dots enclosed in circles. Those of Lannoy 

 unfortunately do not extend far enough to afford a satisfactory veri- 

 fication throughout the range, but we have no reason to distrust our 



