122 MESSES. A. Y. HAECOUET AND W. ESSON ON THE LAWS OE CONNEXION 
ditions, the intervals t x — 1 0 , t 2 —t x , See. would be equal. But, as it is, one condition 
varies, namely, the quantity of hydric peroxide in the solution ; and as this quantity 
diminishes, the amount of chemical change in a unit of time diminishes, or the time 
required for the accomplishment of a unit of chemical change increases. The former of 
these (the amount of chemical change occurring within a given time) was the quantity 
which we were able to determine when investigating the reaction in which hydric per- 
manganate is gradually reduced by an excess of hydric oxalate. The latter (the time 
required for a given amount of chemical change) is that which we are able to measure 
in the experiment which we have described. Either determination provides us with the 
means of calculating the relation between the amount of chemical change and the 
varying condition, that is, the continually diminishing amount of one of the active sub- 
stances. 
The following Table contains the results of one of our first sets of experiments. The 
standard solutions employed in it and in subsequent sets were (1) dilute hydric sulphate 
containing ‘37 grm. in a cub. centim., (2) a solution of potassic iodide containing ‘06 
grm. in a cub. centim., (3) a solution of sodic peroxide containing -00127 grm. in the 
same volume. Of the first of these 100 cub. centims. were taken and 10 of each of the 
others. The total volume of the solution was very nearly 1 litre. The measures of 
hyposulphite were such that 21-45 of them were equivalent when determined by per- 
manganate to the measure of sodic peroxide. Before starting the experiment, by adding 
the solution of peroxide, half a measure of hyposulphite was introduced. At the mo- 
ment, then, of the first appearance of the blue colour, from which moment the observed 
times in column II. date, the amount of peroxide in the solution measured in drops of 
hyposulphite, was 20-95. The numbers in column I. express the quantities of peroxide 
present in the solution at the observed times, those in column IV. the intervals between 
two successive observations, and those in column III. the amounts of chemical change 
that occurred m those intervals. 
We shall find it convenient to speak of such a series of observations made after the 
addition of successive measures of hyposulphite as a set of experiments, and to apply 
the term experiment to each addition of hyposulphite and the two observations which 
determine the corresponding interval. 
