by Displacement in their own Mother-liquor. 31 



arid it is only in such conditions that operations of this kind 

 can be carried out successfully. 



Before bringing the crystals together with the mother-liquor 

 in the specific gravity bottle, the operator must realize that their 

 common temperatirre when mixed, is to be as nearly as possi- 

 ble exactly that of crystallization or equilibrium (T) ; and he 

 must take such measures as his experience dictates to arrive at 

 this end. Preliminary experiments on a somewhat extensive 

 scale are absolutely necessary, and the success of an operation 

 depends almost entirely on the operator and the trouble that 

 he is prepared to take. 



Table II gives for each salt, MR, the temperature, T, of 

 equilibrium between crystals and mother-liquor, and, in con- 

 densed form, the experimental data of the determination of S, 

 the specific gravity at T of the mother-liquor, that of water at 

 the same temperature being unity ; of m, the concentration of 

 the mother-liquor in gram molecules salt per 1000 grams water, 

 and of D 1? D 2 , D 3 , the three observed values, as well as D, the 

 finalty accepted value, of the specific gravity of the salt, all at 

 T and referred to that of water at the same temperature as 

 unity. 



The letters and suffixes have the same significance as in 

 Table I. 



The figures in line T show how uniform the temperature 

 was during the period over which the experiments were spread. 

 All the experiments were made between the 12th and 22d of 

 July, 1904, with the exception of those on caesium bromide, 

 which were made on August 10th. By that time the anti- 

 cyclone had begun to break and the value of T for this salt is 

 21-4:°. For all the other salts, T lies between 22*8° and 24-3°. 



During the wdiole of the period the barometer was very 

 steady, varying between 758 and 761 millimeters, and the 

 relative humidity of the air varied between 40 and 50 per cent. 



Of the three values D 15 D 2 , D 3 for the specific gravity of the 

 salt, D, is obtained directly from the first portion of the salt, D 2 

 from the sum of the two portions, and D 3 is derived from D 1 

 and D 2 by subtraction. 



D 2 represents very nearly the mean of D 2 and D 3 and is the 

 accepted value for the majority of the salts. It is expressed 

 to three places of decimals, of which units in the second place 

 are exact. 



It will be noticed that in the case of rubidium chloride the 

 value of D, is accepted. The second determination depends 

 on the approximate weight of the second portion of salt when the 

 tube was being filled, the exact weighing on the balance of preci- 

 sion having been accidentally omitted. The operation was how- 

 ever completed, and the calculation made with the approximate 



