CONIHTTIVITY OF SOUM'M HYIMIOXIDK IN Agl'KOl'S SOUTION. 267 



same effect as an error of '00001 in the density, and it is therefore permissible to 

 give the density to 5 places of decimals. 



Our original intention was to measure the densities by suspending a cylindrical 

 sinker in the platinum pot, and determining the loss in weight due to the buoyancy 

 of the soda solution. As the sinker had a volume of 100 cub. centims., it was only 

 necessary to measure the loss in weight within a centigramme, in order to determine 

 the density to four places of decimals. It was thought that by adding successive 

 quantities of water from an accurate burette, and checking at the end the total 

 weight of water added, it would be possible to make a rapid series of accurate 

 observations, and to measure the density at frequent intervals over a large range of 

 concentration with little more trouble than that involved in two or three density 

 determinations made by the ordinary method. In this we were disappointed, at 

 least as regards the more concentrated solutions, for 



(1.) The viscosity of the 50-per cent, solution was so great that a sensitive balance 

 required several minutes to show a displacement, even when the weight in the pan 

 was altered by I centigramme or 2 centigrammes at a time ; and 



(2.) The heat generated by the addition of water was so great, and the temperature 

 adjustment so slow, that at least an hour was required before an observation could 

 safely be taken ; a surprisingly large amount of stirring was also required before the 

 solution was sufficiently uniform to give a constant reading. 



For these reasons the method, though excellently adapted for more dilute solutions 

 in which there is no marked heat evolution, proved so tedious in case of the 

 concentrated solutions that it was abandoned in favour of a pyknometer. Even 

 when using a pyknometer, the densities of the concentrated solutions could not be 

 determined without considerable trouble, for many hours were required before the 

 freshly diluted solutions were free from minute air bubbles, and the temperature 

 adjustment was so slow that a 50-cub. centim. pykuometer could not safely be 

 adjusted in less than an hour. 



Altogether seven standard solutions were independently prepared by the method 

 described in Part I. One of these was used only for conductivity measurements. 

 Density observations were made on all the other six. In order to show the extent of 

 the agreement in the values obtained from these different solutions, a list is subjoined 

 of all the density measurements in the immediate neighbourhood of 50 per cent. 



2 M 2 



