Displacement in their own Mother-liquor 203 



centimetres, had an external diameter such that it could just 

 pass freely through the neck of the specific gravity bottle. 

 The wide end was closed with a glass stopper and the narrow 

 end with a small india rubber cork. 



It was the custom to work so as to have about 15 c.c. of 

 dry salt to be added in two charges to the specific gravity 

 bottle. These charges were intended to be nearly, though not 

 quite, equal. The available supply was distributed between 

 two weighing tubes by approximate weight, after which the 

 exact weight of each portion was determined in the usual way. 

 The two portions of caesium chloride weighed respectively 

 JJ-I22Q and 26-6220 grammes, so that in the first determination 

 of specific gravity 22-1229 grammes and in the second 48-7449 

 grammes were concerned. It is not immaterial whether the first 

 portion is charged into the empty specific gravity bottle and 

 the mother-liquor poured over the dry powder, or is charged 

 into the bottle which is already about half full of mother-liquor. 

 In the former case the elimination of the entangled air is 

 difficult and takes time, during which it is not easy to prevent 

 the temperature getting out of hand. By the latter process 

 very little air is carried past the surface of the liquid and very 

 little stirring with the thermometer, which is required on other 

 grounds, suffices to eliminate it. 



Owing to the readiness with which these salts crystallise 

 and to the slowness with which all salts dissolve in an almost 

 saturated solution, the temperature of the mixture of salt and 

 inotht r-liquor, during the adjustment of level in the specific 

 gravity bottle, must on no account be permitted to fall below 

 T by even O'Oi, nor should it be allowed to rise above it by 

 more than 0*1. The regulation of temperature was effected 

 < ntiivlv with a standard thermometer divided into truths of a 

 degree, each tenth occupying a length of rather more than 

 one millimetre on the stem. I lu thermometer which forms 

 part of the specific gravity bottle is used chiefly as a stopper of 

 convenient form. So soon as the level of tin- liquid has been 

 ted in the bottlr. it H weighed. The tnnprrature and 

 ii- of the air are kept account of for the reduction of all 

 weights to the vacuum. 



