212 MR J. Y. BUCHANAN ON THE 



and Rbl (2 12 '5), yet the solubilities in each pair respectively are very diflFerent. 

 The lowest solubilities are on the diagonal KCl- Csl, and the highest solubilities on the 

 diagonal KI-CsCl. RbBr, which occupies the middle place on both these diagonals, 

 is also in the middle of the middle column and of the middle line, and is the centre 

 of the ennead. Its solubility, besides being nearly the average of the group, has a 

 symmetrical position with respect to those of the other salts. On one diagonal the 

 solubility of its neighbours is lower, on the other higher, than its own. In its column 

 the solubilit)^ of its neighbours is higher, in its line it is lower, than its own. 

 Turning from the molecular solubilities in sub-table (e) to the ordinary solubilities 

 given in sub-table (d), we see that the positions of Csl and KCl are reversed ; the least 

 soluble salt of the ennead is KCl, with 355 '24 grams, and next to it comes Csl, with 

 921 '80 grams per 1000 grams of water. Other great differences occur which are 

 obvious on inspection and need not be further referred to here, because in the research 

 only the molecular weights of the salts are taken into account. 



In compartment (h) we have the values of S, the specific gravity of the mother- 

 liquor at T, referred to that of distilled water of the same temperature as unity. These 

 numbers cannot, as they stand, be compared with each other because they refer to 

 solutions of such different concentrations. They enable us, however, to arrive at the 

 increment of the displacement of 1000 grams of water caused by its being saturated 

 with the particular salt at T. Thus, taking again caesium chloride as an example, we 

 have for the weight of salt dissolved in 1000 grams of water 



tv = m.CsCl = 2048-34 grams. 



Adding 1000 grams to this, we have for the weight of the solution 



W = 1000 + «« = 3048-34 grams. 



The specific gravity (S) being r9101, the displacement of the solution is 



W 

 A = — - = 1595 '90 grams of water, 

 S 



whence the increment of displacement of the water by its saturation with the salt is 



w = A - 1000 = 595-90 grams, 



and the mean increment of displacement per molecule is 



- = 49'021 grams. 



TO 



m. MR + 1000 

 Q = A = displacement of the mass of mother-liquor containing 1000 grams of water. 



A- 1000 = V = increment of displacement due to dissolution of m.MR in 1000 grams of water. 



In compartment (/) we have the value of — for each member of the ennead. 



m 



§ 129. Before commenting on the numbers in the table, it is important to form a 

 clear conception of their physical meaning. We shall best arrive at this by returning to 

 our detailed example of chloride of csesium. As the quantity of saturated solution 

 which contains 1000 grams of water weighs 3048 "34 grams and displaces 1595*90 grams 



