Duane — Velocity of Chemical Eeactions. 355 



The particular form represented (Fig. 4) was adopted, first, 

 in order that the temperature of the system should remain that 

 of a bath in which the spiral is immersed owing to the large 

 surface presented to the bath ; and second, in order that the 

 tube might be filled, and the first reading of the position of 

 the mercury column taken as soon after the reaction started as 

 possible. The liquid is first poured in at C and allowed to fill 

 the spiral, the tube A B and the cup A. Mercury is then 

 poured into A and finally the stopper inserted at C. A little 

 practice in manipulating the stopper and tilting the whole 

 tube will enable one to set the dividing surface between the 

 mercury and the other liquid at any desired point in the capil- 

 lary tube. The tube A B is graduated or a graduated scale is 

 fastened to it. 



In most cases the change in the volume of a system is small. 

 Hence, if the temperature of the apparatus varies during the 

 reaction, even by a small amount, the consequent change in 

 volume will be a large fraction perhaps of the change we wish 

 to measure. It is, therefore, necessary to immerse the spiral 

 tube in a delicate thermostat. In the following experiment on 

 the inversion of a 25 per cent solution of cane sugar the 

 electrical thermostat described by my assistant Mr. Lory and 

 myself in this Journal for March, 1900, was used. The tem- 

 perature of the bath did not vary as much as g-oVo"^ °^ a degree 

 except once, and then the variation was only about tAtf^ °^ a 

 degree. 



In this experiment the spiral tube contained about 100 cc of 

 the solution. The length of the capillary tube A B was 36 cm , 

 and its cross section about l sq mm . The temperature was 

 25°-8T2 C. 



The first two columns of the following table contain the 

 readings of the end of the mercury column, on a metal scale 

 attached to the capillary tube, together with the corresponding 

 intervals of time t in minutes. 



After allowing the apparatus to stand 24 hoars and the 

 reaction to become practically completed, the bath was heated 

 up again to 25°'872 C, allowing all of the mercury which had 

 been drawn into the spiral to run out. The end of the mer- 

 cury column then stood at the mark -20, which is the zero cor- 

 responding to zero quantity of cane sugar in the solution. 

 The third column in the table contains the readings referred 

 to this zero. 



Under the assumption that the volume of the solution is an 

 additive function of the constituents, these latter distances rep- 

 resenting the changes in volume should be proportional to the 

 quantities of cane sugar left in solution. The last column 



