SPECIFIC GRAVITY AND DISPLACEMENT OE SOME SALINE SOLUTIONS. 187 



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 attri- 

 buted to errors of observation. 



They persisted while four series of observations 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. 



Throughout each series of experiments the temperature of the solution remained 

 absolutely constant at 19*50° C. After the removal of hydrometer A from the experi- 

 mental solution, on the completion of the fifth series of observations, the solution was 

 stirred carefully with the standard thermometer, and its temperature was found to be 

 19*50° C, that of the air being 19"30° C. It was not until after these observations 

 had been made that a cloudiness indicating the commencement of crystallisation 

 appeared in the solution. It increased rapidly, and the temperature rose smartly to 

 23 '16° C. and remained constant from 1.10 p.m. to 2.35 p.m. — a period of 85 minutes 

 — when the temperature began to fall. 



A careful record of the thermal and other observations throughout the whole 

 experiment was kept, and the following is a resume of these data : — 



Weight of solution + cylinder =1270*190 grams. 



Weight of cylinder = 463*580 „ 



Weight of solution taken for observations 



with the hydrometers = 806*610 ,, 



This solution was 7*225 CaClz+lOOO grams of water, and contained 44*48 per 

 cent. CaCla- 



§ 106. Thermal Data. — When the hydrometer A had been removed from the 

 solution after the fifth series of observations, the time was 1.5 p.m. The solution was 

 stirred with the thermometer, gently, and the temperature noted at 1.8 p.m. It was 

 at this time that the crystals appeared in the solution, and its temperature rose in less 

 than one minute to 23*16° C. and then remained stationary until 2.35 p.m., while that 

 of the air in the room varied only between 19*2° and 19*4° C. When the tempera- 

 ture of the crystals and the solution had fallen somewhat the cylinder was placed in 

 water of 19*3° C. and cooled to 19*5° C, when the mother-liquor was found to have the 

 specific gravit)'^ 1*423500 and to contain 42*33 per cent. CaClg. 



§ 107. Rate of Cooling of Original Solution. — The crystals, together with the 

 mother-liquor in the cylinder, were then heated to a temperature of 30° C. by placing 

 the cylinder in a water-bath of that temperature and keeping it there until the crystals 

 were re- dissolved. The system was then allowed to cool in the air, the temperature of 

 which remained constant at 19*3° C, and the temperature of the cooling liquid was 

 taken at intervals of 30 seconds. 



The series of observations extended over 4 1 minutes, during which the temperature 



