Dissociation of Compounds in Water, 467 



investigated, a stirrer of silver plated with gold by electrolysis 

 was employed. A glass cover was also used for the inner 

 vessel instead of a plate of brass covered with asphalt. 



The Method of Work. 



The compounds used were purified by the methods best 

 adapted to the different substances and standard solutions 

 prepared. 



The freezing-point of exactly a litre of distilled water, 

 which had been cooled nearly to zero before it was placed in 

 the inner vessel, was determined each morning. This was 

 found to differ very slightly from day to day. This slight 

 difference was doubtless due to small changes in the large 

 bulb of the thermometer, which was about 14 centim. long 

 and 1*5 centim. in width. 



A convenient number of cubic centimetres was removed 

 from the litre of water by means of a graduated and calibrated 

 pipette, and an equal volume of the standard solution added. 

 The freezing-point of this new solution was then determined 

 after it had been carefully mixed. 



The vessel containing the solution was then removed from 

 the cold bath and the ice which had formed was allowed to 

 melt. Again a certain number of cubic centimetres was 

 removed from this solution, and exactly an equal number of 

 the standard solution added, and the freezing-point of this 

 new solution determined. This was continued as long as it 

 seemed desirable to concentrate the solution to be investigated. 

 Thus all solutions were prepared directly from the original 

 standardized solution, it was not possible to measure the 

 freezing-point of more than four or five concentrations in 

 one day. Every evening the vessel containing the solution 

 was emptied, and on the following morning the freezing- 

 point of a litre of pure water determined. A sufficient volume 

 of the water was removed and of the standard solution added 

 to make the concentration slightly greater than the last 

 employed. This new solution was then concentrated and the 

 freezing-points determined as on the preceding day. 



The change in volume produced when the solution of the 

 compound to be investigated was added to the water was so 

 slight for the very dilute solutions employed that it can be 

 entirely neglected. 



During the cooling the solution must be stirred gently but 

 continuously. With the form of stirrer employed, a very 

 gentle movement was quite sufficient to keep the liquid 



212 



