chemical change big measurement of the gases evolved. 597 
due to the iodine disappearing at the same instant. This result 
was repeated again and again. Sometimes readings taken only 
•2 c.c. from the end-point showed no departure from the general 
course of the reaction ; in fact, after the retardation was first 
detected in a particular experiment, there was never an evolution 
of more than ‘2 c.c. of gas. It is not easy to speculate as to the 
cause of this strange phenomenon. 
In the following tables are given the observations taken in two 
representative experiments in which nickel carbonyl was in large 
excess. The solutions of nickel carbonyl and iodine used in these 
experiments were of strengths in the ratio of 5 to 6‘5, and it will 
therefore be seen that in experiments A and B the amount of 
nickel carbonyl present in the reaction mixture was equal to 6'5 
and 125 times the equivalent amount of iodine respectively. 
Experiment A. 
Nickel Carbonyl solution ... 25 c.c. 
Iodine „ ... 3 c.c. 
Alcohol ... ... ... 10 c.c. 
Temperature 0°. 
c.c. 
minutes 
c.c. 
minutes 
0 
0'03 
16 
2-45 
2 
0-15 
18 
314 
4 
0-27 
20 
3-91 
6 
0-41 
21 
4-33 
8 
0-63 
22 
4-75 
10 
0-96 
23 
5-19 
12 
1-37 
24 
end-point 
14 
1-87 
Experiment B. 
Nickel Carbonyl ... 26 c.c. 
Iodine ... ... 1'6 c.c. 
Alcohol to make 38 c.c, 
39—2 
