6 
DR. ANDREWS ON THE CONSTITUTION AND PROPERTIES OF OZONE. 
at the beginning' of the experiment, in which it would be at the end. The same 
volume of dry air was passed through the apparatus at the conclusion of each expe- 
riment. 
It is rarely necessary in chemical investigations to apply a correction to the direct 
indications of the balance for changes in the temperature and pressure of the atmo- 
sphere, during the interval between two successive weighings. By preserving the 
apartment at a pretty uniform temperature, the corrections for thermometric changes 
may be confined within very narrow limits, but the movements of the barometer are 
not under our control ; and when, as in these experiments, a period of two and some- 
times of three days elapsed between the first and second weighings, it occasionally 
happened that the change in the atmospheric pressure was considerable, and an 
appreciable error (amounting in some instances to nearly 0*002 grm.) would have 
occurred, if no correction had been applied^. 
To ascertain how far the action of the apparatus might be relied on, one or two 
preliminary experiments were made, which gave very satisfactory results. The vessel 
D, containing pure water, E, sulphuric acid, and another Liebig’s condenser, also 
containing sulphuric acid, having been interposed between E and F, 3*5 litres of 
oxygen gas not containing ozone, followed by 1 litre of atmospheric air, were passed 
through the apparatus. The time occupied in the passage of the gas was about five 
hours. The vessel D lost 0*0311 grm., while E gained 0'031.5 grm., the third vessel 
not sustaining any appreciable change of weight. If, therefore, D and E had been 
weighed together, the change of weight would have been only 0*0004 grm. In an- 
other experiment, in which a solution of strong caustic potassa was placed in D, the 
loss of D was 0*0175 grm., and the gain of E 0*0172 grm., the difference being less 
than one-third of a milligramme. Other experiments of the same kind, with differ- 
ent solutions in D, gave similar results. It is evident, therefore, that at the rate at 
which the gas traversed the apparatus, the whole of the moisture carried off from the 
liquid in D was retained by the sulphuric acid in E. 
To determine whether a notable quantity of iodine would be carried over by the 
current of the gas from D to E, a solution of iodide of potassium containing a large 
* This correction was calculated as follows : — To the volume iii cubic centimetres of the solution of iodide 
of potassium in D and of sulphuric acid in E, was added the volume of the glass of which the vessels D and E 
were formed. From this was deducted the volume of the weights employed Let V be the difference of the 
volumes so found in cubic centimetres ; p and p\ the atmospheric pressures in English inches at the first and 
second weighings ; t and the corresponding temperatures in Centigrade degrees ; x, the weight, in grammes, 
of a volume of air equal to V, measured under the pressure p, and at the temperature t ; x\ the weight of the 
same volume of air at p' and f'. Then, since 1 cub. cent, air, at 0°, and under a pressure of 29’92 inches, weighs 
0-00129 grm.. 
,=v(r 
1 
p. 
1 
+ 0-00367<' 29-92 l-j-0-00367.^ 29-92 
).o. 
00129. 
The value of — x is to be added to, or subtracted from, the increase of weight, as found by direct experiment, 
according as it is a positive or negative quantity. 
