SIE B. C. BRODIE ON THE ACTION OF ELECTRICITY ON OASES. 
93 
We have also for the probable error of a single experiment : — 
probable error of a single experiment = \/b X p. e. of result 
=\/5x-076 
= 0-17, 
3-01 + 0-17=3-18, 
3*01— 0-17=2-84. 
Three experiments are within and four experiments outside these limits. 
If in the case of these five experiments we compare the total oxygen in the gas as 
estimated by these two methods (that is to say, the sum of the quantities given in 
column III. in the two Tables respectively), it appears that this total oxygen, estimated 
by the contraction, amounts to 89*71 cub. centims. against 84-21 cub. centims. as the 
same quantity estimated by the other method. These quantities are proportional to the 
numbers 100 and 93-95. The number 93-95 is below the average arrived at from the 
fourteen experiments before given, namely 95-8 ; and it may be noticed that the value 
of the ratio r in the first Table is below the average value of the same ratio in the 
former system of experiments, 2-9. But the result, in the case of so few experiments, 
is less trustworthy than the preceding. 
These experiments supply an important link in the chain of evidence absent in my 
previous experiments, and demonstrate that not only does the gas absorbed by hypo- 
sulphite occupy twice the space occupied by the volume of oxygen absorbed by neutral 
iodide of potassium, but also that it consists of three times that quantity of oxygen 
and of oxygen alone. 
I may here mention that when the electrized carbonic acid is passed through a solu- 
tion of hyposulphite of soda rendered strongly alkaline with carbonate of soda, the 
diminution in volume is the same as when the gas is passed through neutral hyposul- 
phite — a result quite different to that observed in the case of electrized oxygen*, and 
due doubtless to the presence of the large proportion of carbonic acid, which, as will be 
seen, modifies other reactions also. 
In my previous memoir I have investigated the action of ozone upon a solution of 
protochloride of tinf, and I have shown that the oxidation there effected by the ozone is 
equal in value to three times the “ titre ” of the gas, and also that a diminution in the 
volume of the gas occurs equal to twice that “ titre.” The evidence which I have given 
of these facts is, I believe, perfectly valid ; but the result is not easily ascertained, owing 
to the difficulty of disengaging and separating the effects of the ozone from the effects 
of the oxygen with which it is associated ; but in the present form of experiment, in 
which the ozone is so largely diluted with carbonic-acid gas, and in which the proportion 
of oxygen present in relation to the total volume of gas is so small, the influence of the 
associated oxygen is reduced to a minimum, and the oxidation and diminution in volume 
are those due to the ozone alone. This point is demonstrated by the concordance of the 
* Philosophical Transactions, loc. at. p. 468. 
t Ibid. loc. cit. p. 479. 
