26 J. Y. Buchanan — Specific Gravity of Soluble Salts 



may call its birth, and by making the maintenance of this tem- 

 perature a conditio sine qua non of every manipulation dur- 

 ing which the two are brought together again, errors due to 

 uncertain solubility are eliminated, and contamination of valu- 

 able preparations is avoided. It is therefore by the immersion 

 of each salt in its own mother-liquor that I determine its dis- 

 placement ; and this, combined with the weight of the salt 

 and the specific gravity of the mother-liquor, gives the speciiic 

 gravity of the salt. 



It is obvious that the method is applicable only to salts 

 which have a mother-liquor, such as KC1 ; RbBr; CaCl 2 ,- 

 6H 2 ; BaC]„2H 2 ; it is inapplicable to salts such as CaCl 2 ; 

 BaCl 2 ; and the like, which have no legitimate mother-liquor. 



The anticyclonic meteorological conditions which pre- 

 vailed during the greater part of July and August 1904 were 

 very favorable to this class of work. The anticyclone began 

 to give way when the work was nearly finished, and it was 

 evident that, in the absence of artificial arrangements for the 

 preservation of a constant laboratory temperature, this class of . 

 work cannot be carried on easily or satisfactorily except in the 

 hottest summer weather. 



It is an essential condition of success that the work be car- 

 ried on in a room, for the time being, especially devoted to the 

 purpose, and occupied by one investigator. He must have in it 

 everything that he requires, including his balance. The win- 

 dow of the room must face the north, and the precautions 

 generally to be observed are similar to those prescribed by 

 Bunsen for the practice of his gasometric method. 



The salts used in this research were the chlorides, bromides 

 and iodides of potassium, rubidium and caesium. The rubidium 

 and CEesium preparations were from the works of Schuchardt 

 in Goerlitz and were of the highest degree of purity. The 

 potassium salts were also unexceptionable as regards quality 

 and were supplied by Merck. All of these salts dissolve easily, 

 and most of them abundantly, in water. They also crystallize 

 with great readiness. 



The first operation is to prepare a hot solution of the salt 

 such that, after standing over night, or for such length of time 

 as may be deemed sufficient, it shall furnish about 60 cc of 

 mother-liquor and about 15 cc of crystals. In the case of 

 the potassium salts there was no difficulty, as their solubility 

 at all temperatures is well known. The solubility of the rubi- 

 dium and csesium salts had to be determined, at least approx- 

 imately, in each case, in order to economize the costly material. 

 The following simple method furnished the required informa- 

 tion easily and expeditiously. A suitable vessel, beaker or 

 flask, is weighed empty, and then with 25 grams of distilled 



