120 MESSES. A. V. HAECOUET AND W. ESSON ON THE LAWS OF CONNEXION 
was desired to collect a fresh series of drops. The width of the bottle containing the 
standard solution is so great, in comparison with the quantity of solution taken for any 
one set of experiments, that the available length of the siphon and the rate of flow, 
upon whose constancy that of the drops depends, varies in no appreciable degree. 
Numerous determinations were made with standard iodine solution of the values of 
drops thus collected, and they proved to be perfectly equal. To introduce a drop into 
the fluid in the cylinder, the end of one of the tubes thus charged was dipped into it 
and moved up and down, while an active stirring was carried on by means of the bubbles 
of carbonic acid. 
When, then, the preparations already described had been completed and a sufficient 
number of tubes, each loaded with its drop, were lying in readiness, it remained to add 
to the contents of the cylinder a measure of hydric peroxide, and to mix it as thoroughly 
and as rapidly as possible with the rest of the fluid. Since, however, the addition and 
mixing are far from being instantaneous, an experiment was not made to date from this 
point, but from the moment of the first appearance of the blue colour. In order that the 
second at which this change occurred might be accurately noted, the cylinder was placed 
on a sheet of white paper in a good light, and opposite to it was stationed a clock 
beating seconds. The paper lay on an iron plate, one end of which was heated more or 
less gently by a lamp according to the temperature at which the set of experiments was 
to be performed and that of the surrounding air. By moving the cylinder nearer to or 
further from the heated end of the plate, the temperature of the fluid could be conve-i 
niently regulated. The observations were made by looking down upon the column of 
fluid and watching the appearance of the disk forming its upper surface, listening at the 
same time to the beat of the clock and counting the seconds. So suddenly does the blue 
shade pass over the clear and brightly illuminated disk, that a practised observer can 
generally feel sure as to the second in which the change begins. And where the reaction 
is proceeding very rapidly it would often be possible to subdivide the second. As soon 
as the observation had been made* a drop of hyposulphite was introduced, which speedily 
restores the liquid to its normal colourless condition. The time that elapses between 
two successive appearances of the blue colour becomes continually greater as the amount 
of peroxide in the solution diminishes, and finally the last measure of hyposulphite 
requires for its conversion more iodine than the residual peroxide can furnish, and the 
blue colour never returns. The values of the measure of peroxide and of the drops are 
readily compared by means of a standard solution of potassic permanganate. To apply 
this reagent to the estimation of sodic hyposulphite, it is necessary to add to the solution 
potassic iodide and hydric sulphate, together with a little starch. The determination may 
thus be performed directly with the same result as though an acidified solution of potassic 
iodide were first decomposed by permanganate, and the liberated iodine were then used 
to measure the hyposulphite. The relation between the two reactions which occur 
simultaneously in this determination is strictly parallel to that between the reaction of 
hydric peroxide and hydric iodide, which forms the subject, and the reaction of iodine 
