1 



2 



3 



4 



5 



A 



B 



A 



B 



A 



88 



250 



168 



146 



833 



46 



68 



50 



66 



56 



SPECIFIC GRAVITY AND DISPLACEMENT OF SOME SALINE SOLUTIONS. 195 



the following table, the greatest amplitude of the variation in each series given in 

 Table 1 1 a. with those occurring in series made with the same hydrometer, as given in 

 the other table, IIb. 



Series ...... 



Hydrometer ..... 



Amplitudes of Variation < 



^ I Table 11b. 



In series 4 of Table IIb. there are two extreme values of the specific gravity, 

 namely, 1*409696 and l"409818, giving an amplitude of 122, but they are quite ex- 

 ceptional, and if they are omitted the greatest amplitude in the series is 66, so that 

 the mean maximum amplitude in the series made with hydrometer B is &7 , while that 

 in the series made with hydrometer A is 50. 



On examining the figures for the supersaturated solution, their irregularity when 

 compared with those of the G'3 CaClg solution is at once apparent; moreover, the 

 irregularity increases very rapidly in each consecutive series, so that the amplitude of 

 variation is in the first series 88, rising to 250 in the second, then falling to 146, and 

 reaching 833 in the last series, immediately after which crystallisation commenced. 

 I The rate of increase is not regular, for in the fourth series the variation amounts to 



I 146, which seems to show that the solution was for the time being in a state of com- 

 parative calm. 



This table, therefore, serves the useful purpose of indicating the fluctuating 

 j character of the alteration of the specific gravity, while Table IV. shows that in 

 ' spite of these fluctuations there is a definite decrease in specific gravity from the first 

 to the fifth series. 



§ 113. Displacement. — The displacement of the 6 "3 gram - molecule solution 

 throughout the series is for all practical purposes constant, as might be expected, 

 since the solution is quite stable and no disturbing influences, such as the imminence 

 of crystallisation, are present. 



But the displacement in the case of the supersaturated solution is subject to variations 

 corresponding to those of the specific gravity. These afford evidence of considerable 

 and, to some extent, spasmodic acts of expansion and contraction, unaccompanied hy 

 any change of temperature of the solution or of the external pressure to which it ivas 

 subjected. These spasmodic changes of volume exhibit a veritable species of labour, 

 going on in the solution in its efforts to become a mother-liquor. In this it is finally 

 successful, but not before it has succeeded in forcing the door which confned its store 

 i of heat. The birth of the crystal ivas synchronous with, and dependent on, the libera- 

 tion of heat. 



If we consider the mean specific gravities of the five series given in Table IIa., we 

 find a progressive decrease in them from the first to the fifth, with an interruption in 

 the fourth, where a slight increase is observable over that of No. 3. This resultant 

 decrease of the mean specific gravity of the solution is accompanied by a series of 



