12 MR J. Y. BUCHANAN ON THE 



PAR, PAGE 



21 '99°, and the solution remained liquid to the end. The cooling had proceeded 

 for 13 minutes before the temperature fell to 23"16°, and the loss of heat was 

 taking place quite regularly. -The following are the temperatures observed at each 

 ^ minute for 2 minutes before and 2 minutes after the temperature of 23"16° was 

 passed : — 



Time in minutes : -2-0 -1-5 -TO -0-5 00 +05 I'O 1-5 20 

 Temperature: 23-23° 23-21° 2319° 23-17° 23-16° 23-14° 23-12° 23-09* 2307° 



During the 4 minutes the temperature fell 0-16°, whence 0-04° per minute represents 

 the mean rate of fall of temperature when the system has the temperature 23-16° and 

 is cooling in air of constant temperature 19-30° C. 



108. Calculation of Heat liberated during Crystallisation. When crystallisation was started, 188 



the temperature of the system rose in less than a minute from 19-5° to 23 '16°. During 

 this phase the temperature of the cylinder with its contents was raised 3-66°. The 

 heat liberated in this act was found to be 2217 gram-degrees (gr.° C). During the 

 second phase the rate of liberation of heat was equal to its rate of dissipation, which 

 was represented by a fall of temperature of 0-04° per minute. This was maintained 

 for 85 minutes, which requires a liberation of 2059 gr.° C. of heat; so that the total 

 heat liberated in the act of crystallisation was 4276 gr.° C. 



109. Verification of the constitution of the crystals as CaCl26H20. According to Thomsen, the 188 



heat of solution of CaCl26H20 is —4340 gr.°C. ; therefore on thermal evidence alone 

 215-5 grams or 0-984 CaCl._,6H20 has separated out. On the basis of analytical estima- 

 tions made on the supersaturated solution and the mother-liquor, 210-3 grams or 

 0-96 CaCl26H20 must have sei^arated out. The agreement of these two computed 

 values is excellent. 



110. Descri[ition of Tables 11a. and IIb. In Table IIa. are given the individual observations 189 



of specific gravity forming together the five series, of eleven observations each, on tlie 

 supersaturated solution 7-225 CaCl2 when it was exhibiting the state of unrest which 

 preceded crystallisation. In Table IIb. are given the individual observations forming 

 five series of eleven observations each, on the non-saturated solution 6 '3 CaClj. 

 Table lie. contains the imlividual observations forming three series of eleven observa- 

 tions each, on the super.-atiirated solution 7-196 CaClg- It crystallised suddenly after 

 the third series. Table III. forms a time-table of the observations on the supersaturated 

 solution 7-225 CaCl2. 



111. Discussion of conditions of temperature maintained while the operations recorded in 193 



Tables IIa. and IIb. were being made. 



112. Further discussion of Tables IIa. and IIb. Considering the five mean specific gravities of 194 



7-225 CaClg, it is found that the maximum amplitude of variation is 689 units in the 

 sixth decimal place, while the five mean specific gravities of 6-3 CaCl2 exhibit a 

 maximum amplitude of only 26 such units. When the observations of individual 

 series are considered, the maximum amplitude of variation in the fifih series for 

 7-225 CaCl2 is 833 in the sixth decimal place. These large and rapid variations of 

 specific gravity in the supersaturated solution furnish the evidence of the state of 

 unrest existing in it. 



113. The displacement of the solution is subject to variations corresponding to those of the 195 



specific gravity. Tiiey afford evidence of spasmodic acts of expansion and contraction, 

 not accompanied by any change of temperature of the solution or of the external 

 pressure to which it is subjected. They exhibit a veritable species of labour going on 



