Reaction before Complete Equilibrium. 81 



be calculated for each' case. A few examples only are given 

 to make the subject clear. 



Example 1. Ice separates from water or an unsaturated 

 solution that has been over-cooled 1° below the freezing- 

 temperature. The point of equilibrium obtained T' differs 

 from the real one T by 



Cfe-0 _ 0-004x0-1 



C"(t -t ov + K) 30x1 



0°-000013 



for each T^ — T' made =0°'l. 



Example 2. Salt separates from a supersaturated solution ; 

 T' differs from T by 



C(L-t) 0-004x0-1 



for each T 7 — T' = 0°*1 and for an over-saturation (t — £ 0B -|-K) 

 = 1° rise of temperature. 



C. All part*, i. e. the liquid, beaker, stirrer, and thermometer, 

 must instantaneously assume the same temperature, while 

 heat is evolved or absorbed as a result of the reaction. 



The glass beaker and porcelain stirrer of my previous expe- 

 riments were replaced by a very thin nickel-plated copper 

 beaker of about six litres capacity and of 235 grs. weight, and 

 by a nickel stirrer (strong enough to overcome the resistance 

 of the liquid) of 238*5 grs. weight. This had to be done in 

 spite of the fact that the liquid cools more quickly in a beaker 

 of thin metal than in a glass beaker, because the heat-capacity 

 of the glass beaker and stirrer is by no means so small in 

 comparison with the heat-capacity of the liquid that the 

 error arising from their small conductivity could be neglected. 



To provide for the instantaneous equalization of tempe- 

 rature through the liquid, beaker, stirrer, and thermometer, 

 while the reaction was going on, very effective arrangements 

 for stirring were necessary. A double stirrer (St) with two 

 parallel circular plates in which a number of round holes were 

 cut was used, and the plates were so placed that the holes of 

 the upper and lower plates did not coincide. Currents were 

 thus obtained in all directions while the stirrer was moved up 

 or down. The stirring of the liquid was so effectual that 

 when the stirrer moved at the bottom of the beaker the liquid 

 still moved very perceptibly in its uppermost layers. The 

 photographing of the results nevertheless showed that when 

 during the reaction the solid separates throughout the whole 

 liquid (<?. </. when ice separates from over-cooled liquids or 



Phil. Mag. S. 6. Vol. 2. No. 7. July 1901. G 



