Volumes of Salt-Solutions. 



189 



it is without influence on the results. Care must, however, 

 be taken to employ an excess of the other solution ; but as no 

 appreciable effect is produced by even as much as 6 or 8 

 cubic centim. of excess, there is no difficulty in this. 



Table VI. gives the results thus obtained. From it, it is 

 evident the precipitation of one molecule of BaS0 4 is attended 

 by the same volume-change so long as the precipitation is 

 effected by a sulphate which contains no water of constitution, 

 though it may or may not contain water of crystallization. 

 When, however, the sulphate contains water of constitution, 

 then there is less expansion, and the diminution is comparable 

 with that observed in Table V. Now adding together the 









Table VI. 





A. 



B. 



Expansion. 



Difference. 



Eemarks. 



BaCl 2 . 



Na 3 S0 4 



CuS0 4 



ZnS0 4 

 NiS0 4 

 MnS0 4 



435 

 439 

 377 

 37-8 

 37-2 

 38-6 



J43-7 



-6-0 

 -5-9 

 -65 

 -51 



Mean of 2. 

 3 concordant. 

 Mean of 2. 



„ „ 2. 



5> ?> 2. 



j) » 2. 





Difference = 



43-7 — expansion of CuS0 4 



&c. 



mean difference in this Table (5*9) and that obtained in 

 Table V. (6'8) we get 6'35 ; which is as close an approxima- 

 tion as I can make at present to the difference in molecular 

 volume produced by a molecule of water of constitution. It 

 is to be noted that this is a + quantity; and if the molecular 

 volume of water of solution be 18 ; then that of water of con- 

 stitution is 24" 4. 



The accuracy of the experiments on the volume-change by 

 the precipitation of BaS0 4 can be shown by the following 

 calculation: — 



BaCl 3 +Na 2 S0 4 =BaS0 4 +2JSTaCl. 

 By Table II.:— 



Mol. vol. of BaCl 3 . . . 3626*5 

 „ „ Na 2 80 4 . . . 3616-6 



Mol. vol. of BaS0 4 . . 

 „ „ 2NaCl + 5400 



Difference . 



7243-1 



51-8 

 7236-3 



7288-1 

 7243-1 



= + 45-0 



