TEiMPERATUEE OF THE RATE OF A CEEEMICAL CHANGE. 
193 
(3) in the same mixture with the addition of a corresponding quantity of hydrogen 
sulphate, were as follows ;— 
Temperatures 
12° 
15° 
18° 
21° 
24° 
27° 
3U° 
Minutes (l) . 
34-9 
25-9 
19-1 
14-6 
10-8 
8-0 
6-1 
(2) . . 
12-2 
8-8 
6-8 
5-0 
4-1 
2-8 
2-2 
„ (3) . . 
60-0 
45-0 
36-0 
26-8 
19-3 
16-2 
107 
At each temperature the times in the third set are approximately 1’8 times those 
in the first set, and 5 times those in the second set. 
No complete set has been made with hydrogen nitrate, but enough observations to 
show that it has an influence on the rate of change quite as unexpected as that of 
hydrogen sulphate, namely, that its addition makes little if any difference. 
The times required for doing the fixed amount of chemical work at 21°, with (a) no 
addition, and then with the addition of equivalent quantities of {h) hydrogen chloride, 
(c) hydrogen sulphate, and (d) hydrogen nitrate, were as follows :— 
a. h. c. d. 
14'6 5'0 26‘2 13"7 minutes. 
Having carried thus far an experimental inquiry which is suggestive of much further 
work, the author ventures to express a hope that it may attract the attention and 
pass into the hands of some younger chemist. The mode of working adds to the 
usual interest of research the particular excitement which attaches to all observations 
and predictions of time, sporting or scientific, wliether it be of the time of a race or of 
the moment of an occultation. 
Lastly, he desires to express his thanks to Dr. Baker and to Christ Church for the 
welcome and the opportunity of work and the help which he has received. 
APPENDIX. By Prof. W. Esson, F.R.S. 
I. The observations recorded in the preceding pages follow the law of connexion 
between chemical change and temperature with great exactness. This law, first 
enunciated in the Bakerian Lecture delivered to the Royal Society in 1895, is 
expressed by the relation 
hjh' = (T/TO'h 
h, k' being the rates of chemical change at absolute temperatures T, T' respectively. 
This relation is independent of the units of measurement of k and T, and in is a pure 
number which expresses the ratio of dkjk to rZT/T. This implies that if at a 
temperature T a small change is made in each unit of temperature, and this change 
produces a corresponding small change in each unit of chemical change, the latter 
2 c 
VOL. COXTI.-A. 
