136 MESSES. A. Y. HAECOUKT AND W. ESSON ON THE LAWS OE CONNEXION 
upon the rate of change independently of the part which it plays in the reaction itself. 
Now, if equivalent quantities of hydric sulphate and iodide caused equal accelerations, 
the replacement in the solution of one of these acids by the other would produce no 
etfect ; but if hydric iodide, like hydric chloride, has a greater accelerating power than 
hydric sulphate, the effect of this replacement would be to cause an acceleration inde- 
pendent of and additional to that which is due to the increase of iodide. When, as in 
the sets of experiments recorded in Tables V. and VII., the hydric sulphate or chloride 
replaced by hydric iodide is but a small fraction of the whole amount in the solution, 
this change does not so affect the rates as to hinder us from observing the result of the 
simple variation of iodide; but when the experiment is pushed further, and a con- 
siderable proportion of the acid is thus changed, the effect of this second variation 
becomes perceptible. With the view of inquiring whether the proportional relation 
between the amount of iodide and the amount of chemical change still holds good when 
the solution does not contain an excess of acid, a number of sets of experiments were 
made with a constant quantity of hydric iodide and various quantities of potassic iodide. 
Here we encountered a fresh difficulty ; the primary reaction no longer followed the law 
expressed by the equation 
y 
and although the measurements of the solutions 
and the observation of the intervals were made with all possible care, we are not able to 
derive from the experimental data any series of values for a, nor therefore to determine 
what function the total amount of change was of the amount of iodide. The following 
Table contains the results of these sets of experiments. To avoid the introduction of 
any other acid besides hydric iodide, a neutral solution of hydric peroxide was used. 
The volume of the solutions was 993 cub. centims., and their temperature 30° C. 
The amount of iodide in a cubic centimetre of each was 15-25 HI and 7 - 28 nKI. 
The amount of peroxide at starting was about -98 H 2 0 2 . The amount of actual change 
during each interval was T3 {H 2 0 2 -\-2H I=2H 2 0-\-I 2 }. 
Table IX. 
78 = 0. 
78 = 1. 
78 = 2. 
78 = 3. 
n= 4. 
n=5. 
78 = 6 . 
Observed 
Observed 
Observed 
Observed 
Observed 
Observed 
Observed 
intervals. 
intervals. 
intervals. 
intervals. 
intervals. 
intervals. 
intervals. 
6-40 
4-05 
2-93 
2-28 
1-85 
1-55 
1-38 
7-40 
4-90 
3-54 
2*75 
2-25 
1-92 
1-72 
9*05 
5-92 
4-33 
3-50 
2-82 
2-40 
2-13 
11-27 
7-58 
5-70 
4-65 
3-76 
3-26 
2-95 
15-30 
10-57 
8-15 
6-80 
5-52 
4-74 
4-32 
24-30 
59-82 
17*41 
56-07 
13-82 
12-20 
9-65 
8-06 
7-93 
The first, and perhaps the second of these sets of experiments, gives a logarithmic 
curve; the remainder depart more and more widely from this relation. The cause of the 
departure is probably the same as that which prevented the observation of the law of 
