No. 10. [From The American Journal of Science, Vol. xxi. 

 January, 1906.] 



ON A METHOD OF DETERMINING THE 

 SPECIFIC GRAVITY OF SOLUBLE SALTS 

 BY DISPLACEMENT IN THEIR OWN 

 MOTHER-LIQUOR; AND ITS APPLICA- 

 TION IN THE CASE OF THE ALKALINE 

 HALIDES 1 



DURING the summer of 1904 I was occupied with the 

 determination of the specific gravity of various saline solutions 

 by the hydrometric method, which I designed for use on board 

 the "Challenger" and have perfected in the course of years, 

 since that date. The most important condition of success 

 with this method is to operate always at the same temperature, 

 and during an operation to keep that temperature perfectly 

 constant. The temperature which I used was 19*5 C., both 

 because a great quantity of similar work has been done at this 

 temperature and because, in the room which it was my privilege 

 to occupy in the Davy-Faraday Laboratory, this temperature 

 is one which is very easily produced and kept constant, so 

 long as the temperature of the air outside does not exceed it. 

 This work was put a stop to by the arrival of the great anti- 

 cyclone of the summer of 1904 which persisted over northern 

 Europe for nearly six weeks and produced tropical conditions, 

 which were evidenced alike by the high temperature of the air 

 an<l by its insignificant diurnal variation. 



In these circumstances I decided to make nsr of tin- time 

 by putting into practice a method of determining the >pecific 

 gravity of soluble salts which I have long intended to try. 



specific gravity of an insoluble substance is dc-tcrmincd 

 by the amount of distilled water which a known weight <>t it 

 displaces. In the case of soluble salts it has been tin custom 



1 Head .a the meeting of the Chemical Society of London on oth April. 

 1905. 



