SPECIFIC GRAVITY AND DISPLACEMENT OF SOME SALINE SOLUTIONS. 11 



PAR. PAGE 



101. Discussion of the values of d^/dm and v/m especially for solutions for which m is less 182 



than 1. 



102. The values of dA-vave discussed. The principal feature of the table illustrating them 183 



is the pronounced expansion which accompanies the dilution of solutions of beryllium 

 chloride for which m is less than 1/16. 



103. The relations between the exponents of the solutions x and m are discussed, and a table 184 



of the values of log A„,/log A,„ for solutions of each of the three salts is given. 



SECTION XV. 



On a Remarkable State op Unrest in a Supersaturated Solution of 

 Calcium Chloride before Crystallising. 



104. The supersaturated solution was 7 '225 CaCl2 + 1000 grams of water. It was expected that 185 



this solution would crystallise easily and furnish a truly saturated solution. As it 

 showed no inclination to crystallise although every opportunity was offered it to do so, 

 it was adopted as an example of a supersaturated solution peculiarly adapted to closer 

 study. Table I. contains the constants of the open hydrometers A and B, as loaded for 

 the experiments of this section, (a) when floating in distilled water, and (6) when float- 

 ing in the supersaturated solution of calcium chloride. 



105. The experiments showing the state of unrest were made 11th May 1910, in the Davy- 186 



Faraday Laboratory. A series of observations had been made with each hydrometer, 

 and further observations were proceeding when it was noticed that discrepancies between 

 successive readings and corresponding ones in the earlier experiments made with the 

 same added weights were occurring, and that these were far greater than any which 

 could be attributed to error of observation. They persisted while four series of obser- 

 vations were made, two sets with each hydrometer, and were so great that in the fifth 

 series of observations it was necessary to reduce the initial added weight in order that 

 the complete series of observations might be made. The temperature of the solution 

 was perfectly constant at 19"5° C. during each series. 



106. After removal of the hydrometer from the experimental solution on completion of the fifth 187 



series of observations, the solution was stirred as usual with the standard thermometer, 

 and its temperature was found to be 19'50°, that of the air being 19"30°. It was not 

 until after these observations had been made that a cloudiness indicating the commence- 

 ment of crystallisation appeared in the solution. It increased rapidly, and the tem- 

 perature rose smartly to 23' 16° C, and remained constantly at that temperature from 

 1.10 p.m. to 2.35 p.m., a period of 85 minutes, when tlie temperature began to fall. 

 The supersaturated solution (7'225 CaClg-l-lOOO grams of water) contained 44'48 per 

 cent. CaClg. When the temperature of the mixture of crystals and solution had 

 fallen someAvhat, the cylinder was placed in water having the temperature 19'3°, and 

 was cooled to 19'5°. The mother-liquor was then found to have the specific gravity 

 1-423500, and to contain 42-33 per cent, of CaClj. 



107. The crystals along with the mother-liquor were then heated in the cylinder to a tempera- 187 



ture of 30° C. by placing the cylinder in a water-balb of about that temperature, and 

 keeping it there until tlie crystals were redissolved. The system was then allowed to 

 cool in the air, the temperature of which remained constant at 19-3°, and the tempera- 

 ture of the cooling liquid was taken at intervals of 30 seconds. The series of observa- 

 tions extended over 41 minutes, during which the temperature fell from 23-82° to 



