SIR B. C. BRODIE ON THE ACTION OP ELECTRICITY ON GASES. 
479 
These experiments are also in accordance with theory ; for it appears from them that 
it is an equal chance that the true value of the ratio 
v-v 1: 
T 
is included within the limits 
T99 and 2 , 05. 
Also, from the probable error of a single experiment, half the preceding observations 
would theoretically be included within the limits T94 and 2T0; four out of the eight 
experiments are within these limits, and four external to them. 
Sufficient evidence is afforded of the value of the oxidation which occurs in the case of 
the contractions considered in Section III. (where the contraction is equal to the “titre” 
of the gas) by the experimental determination of the oxidation effected in the case of 
hydriodic acid ; which oxidation is exactly represented by an amount of oxygen equal to 
that which disappears in the contraction in the case of the strongly alkaline hyposulphite 
of soda, together with the titre of the gas. With the view of determining this point in 
the class of contractions considered in the present Section, I have made various experi- 
ments with protochloride of tin, in the case of which substance the oxidation effected, as 
well as the change in the volume of the gas, may be determined with considerable accu- 
racy. These experiments, however, are attended with peculiar difficulties, not only from 
the facility with which the protochloride of tin is oxidized and the influence which very 
slight variations of circumstances (such as the strength of the tin solution and the rate 
of the passage of the gas) have upon the oxidation, affecting the result in various ways, 
but also from the circumstance that the oxidation effected by the action of the ozone 
and that effected by the oxygen associated with it are in all probability not independent 
of one another — owing to the occurrence of that remarkable induced oxidation which 
has been noticed and made the subject of investigation, in the case of the oxidation of 
the protochloride of tin by chromic and permanganic acids, by F. Kessler*, and also by 
Lenssen and LowENTHALf , so that we cannot'apply a correction for the oxidation effected 
by the associated oxygen on the simple principle employed in the case of hydriodic acid. 
However, by operating with very dilute solutions the influence of these sources of error 
may be, if not entirely destroyed, at any rate very greatly reduced ; and the following 
experiments afford conclusive evidence as to the actual oxidation effected in those cases 
also where the contraction is equal in amount to twice the “ titre” of the gas. 
It appears from the three following experiments, that when an electrized gas is 
passed through an acid solution of protochloride of tin, the total oxidation which takes 
place is equal in amount to that due to the “ titre” of the gas, together with the oxida- 
tion due to a volume of oxygen equal to the contraction which occurs in the experi- 
ment. 
The oxidation of the protochloride of tin was determined by running an amount of 
the tin solution equal to that employed in the experiment into a measured quantity of 
a standard iodine solution greater in amount than that required to effect the oxida- 
tion of the tin. The excess of iodine was estimated with a standard solution of hypo- 
* Pogg. Ann. scvi. 332, and cxix. 218. 
f J. Pr. Chem. lxxxvi. 193; Jahresbcricht, 1862, p. 38. 
