354 



Duane — Velocity of Chemical Reactions. 



Or integrating between t l and t 



k {t-t) = log, 



2-3026 log 10 -±- 

 z 



or 



2*3026 . z. 



k = log 1ft — 



t—t, 6l ° z 



The third column in the table contains the values of 



2-3026 



calculated by this formula, using the value t x = 15 minutes so 

 as to avoid extrapolation. It appears that k as calculated above 



u 



14, 





is not a constant. The decrease in its value indicates that the 

 velocity of the reaction is greater at the beginning or less at 

 the end than would be expected from Gouldberg and Waage's 

 law. During the reaction, of course, the amount of water 

 present changes perceptibly, but not enough to account for the 

 large variation of k. The total change during the entire reac- 

 tion is less than 2 per cent. The deviation from Gouldberg 

 and Waage's law may be due to the relatively large quantity 

 of hydrochloric acid in the solution. To decide whether it is 

 or not will be the object of further investigation. 



The second method is based upon the change in the volume 

 of the chemical system during the reaction. In order to meas- 

 ure the change in volume the system is placed in a spiral glass 

 tube (Fig. 4), on one end of which is sealed a capillary tube A B 

 and on the other end a ground stopper and cup C. The react- 

 ing system may fill the entire spiral or only a part of it, the 

 rest being filled with a liquid that does not combine with the 

 given system. If the volume increases during the reaction, 

 the cup A and most of the tube A B are filled with mercury. 

 If the volume decreases, the cup and only a small part of the 

 tube are filled. Evidently during the change of volume the 

 mercury is drawn in or pushed out through the capillary tube 

 and the positions of the end of the mercury column measure 

 the amount of change. 



