i88o.] 
History of Ozone . 
153 
this was their simplest possible explanation. Four years 
later Soret discovered that a very remarkable reaction 
occurs when electrolytic ozone is allowed to a Ct upon oil of 
turpentine. Its volume is diminished by a volume equiva- 
lent to twice that of the oxygen, corresponding to the iodine 
set free on passing the ozonised oxygen into a solution of 
iodide of potassium. The latter, it will be remembered, is 
the same as the diminution in volume which the oxygen 
undergoes in ozonation, and may be called the contraCtion- 
volume. Hence the two volumes of ozonised oxygen ab- 
sorbed in Soret’s experiments contained not only their own 
volume of oxygen, but that contained in the contraCtion- 
volume, or in all three volumes of ordinary oxygen. The 
density of ozone, therefore, was to the density of oxygen 
as three to two, or 1*6584, the density of ordinary oxygen 
being 1*10.56. 
Soret inferred rather than demonstrated these relations, 
inasmuch as in his first set of five experiments the ratio of 
the total volume of ozonised oxygen absorbed by the tur- 
pentine to the contraCtion-volume was 2*4, and in his second 
set of seven experiments i*8i, both of these results being 
far from 2, the theoretical number. 
However, in 1872, Sir Benjamin Brodie, by the introduc- 
tion of methods of exaCt volumetric character, supplied a 
rigorous experimental demonstration. He obtained in a set 
of eight concordant experiments made with oil of turpentine, 
for the ratio between the whole diminution in the volume of 
the original oxygen, to the diminution in the volume of the 
ozonised oxygen, as a mean result, 3*02 to 2*02. Operating 
in the same manner with a neutral or slightly alkaline solu- 
tion of sodium hyposulphite, he obtained, as a mean result 
of twenty-seven concordant experiments, the same ratio of 
3*02 to 2*02. In these experiments the actual weight of 
the oxygen absorbed could not be determined otherwise than 
by calculation from the alteration in volume. But by the 
oxidation of stannous chloride, under proper conditions, he 
effected a direCt determination, and found that the weight of 
the oxygen absorbed from the ozonised oxygen by the stan- 
nous chloride was almost exaCtly three times the weight 
absorbed from the same gas by potassium iodide. At the 
same time the volume in the first case was almost exaCtly 
twice the contraction volume, as determined by the latter 
reagent. 
