SIE B. C. BEODIE ON THE ACTION OE ELECTEICITY ON GASES. 
445 
mencement of the experiment, by drawing a few bubbles of air through it by means 
of the aspirator, as to occupy the same position as that in which it was finally left at the 
conclusion of the experiment. Before the commencement of the experiment the 
aspirator was completely filled with mercury from the reservoir. 
In Plate LII. fig. 8 a drawing is given of the whole apparatus as arranged for experiment. 
I may here express the obligations which I am under to my assistant, Mr. J. 
Robinson, for the effectual way in which he has aided me in this investigation, 
especially in the construction and use of this apparatus for measuring gases, towards 
the completion and perfecting of which he contributed several valuable suggestions. 
Section II. 
The action of ozone upon iodide of potassium has been investigated by Andrews and 
Tait*, and also by Yon Babo and CLAUsf. These experiments were made in both 
instances with great care ; and my own observations entirely confirm the conclusions at 
which these chemists arrived, and so far present no new feature. It is, however, very 
desirable in so obscure a subject to multiply experiments; and as the following expe- 
riments were conducted in a totally different manner to that in which these chemists 
operated, and illustrate the working of the apparatus and the degree of precision attained 
by it, I shall lay them before the reader. 
A known volume of the electrized gas was drawn over from the gas-holder into the 
pipette and there measured. The gas was then passed through a solution of iodide of 
potassium contained in one of the glass bulbs previously referred to into the aspirator, 
where the volume was again measured. After the experiment the solution of iodide of 
potassium was rendered acid by means of a dilute solution of hydrochloric acid, and 
the iodine formed estimated by a standard solution of hyposulphite of soda. The 
quantity of oxygen equivalent to this iodine is here termed the “Titre” or “ Iodine- 
titre” of the gas; it is a quantity which for the same gas is constant, and which may 
be estimated with the greatest precision : I have therefore selected this quantity as the 
unit with which other analogous quantities are compared. 
It is to be observed that ozone is by no means the unstable thing which it is generally 
imagined to be. The concentrated sulphuric acid over which ozone has been long 
kept becomes singularly free from colour and of a peculiar brightness. This doubtless 
arises from the oxidation by the ozone of the particles of organic matter otherwise inva- 
riably present in it ; but when the sulphuric acid has attained this condition, the electrized 
gas may be kept over it for many hours at the temperature of the laboratory without 
appreciable alteration of the “titre.” Thus in an experiment not made for this purpose, 
and made without any special precautions for the preservation of the gas, the “ titre ” 
of a gas, twenty-four hours after the gas had been submitted to the electric action, was 
equivalent to 28’25 cub. centims. of hyposulphite of soda ; after sixty-six hours the 
* Philosophical Transactions, 1860, p. 113. 
t Annalen tier Chemie und Pharmacie, Supplementband ii. (1863), p. 297. 
3 p 2 
