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DE. ANDEEWS AND PEOFESSOE TAIT ON THE 
f3. In another vessel, having a reser^^oir of the capacity of 0-8 cub. cent., active sparks 
gave, in fifteen minutes, 4 miUims. of contraction. After fifteen minutes more of sparks 
there vras no additional contraction. 
The silent discharge was now passed for fifteen minutes, and increased the contrac- 
tion to 20 milhms. ; in fifteen minutes more, the entire contraction was 31 millims. 
Four strong sparks reduced this to 22-5 millims., six or seven more to 16 millims., 
seven more to 11 millims., and sparks, continued for ten minutes, left 4 millims. of 
permanent contraction. 
y. In a third vessel, of about the same capacity as the last, sparks gave a final con- 
traction of 7 '5 millims.; while the silent discharge, pushed to its limit, increased the 
contraction to 90 millims., corresponding to about one-twelfth of the entire volume of 
the gas. This contraction was almost exactly destroyed by heat. 
Before leaving this part of the subject, we should mention that, when a full contrac- 
tion is obtained by means of the silent discharge, it will be found very slowly to dimi- 
nish from day to day. We have not ascertained whether, at the end of a very long period 
of time, the original volume of the gas would be recovered. At 100° C., the contraction 
diminishes much more rapidly than at ordinary temperatures. Thus it appears that the 
state produced by the electrical discharge is not permanent, even at common tempera- 
tures, and that it becomes more unstable as the temperature rises, till at 270° C. it is 
rapidly destroyed 
We next proceeded to examine the volumetric changes which occur- when oxygen, 
contracted by the electrical discharge, is brought into contact with other bodies. 
The first body we tried was mercury^ the physical changes produced on which by ozone 
are known to be very remarkable. When a capsule containing this metal is broken in 
a tube of oxygen gas through which the sHent discharge has been passed, the mercury 
instantly loses its mobility, and, if gently shaken, covers the interior of the tube with a 
brilliant mirror. As the action continues, the mirrored surface breaks up, and the coat- 
ing becomes converted into a blackish semipulverulent substance. Unless the tube be 
very violently shaken, the ozone reactions will not be entirely destroyed, until the mer- 
cury has been for some hours in contact with the gas. 
To determine the volumetric changes, a thin capsule, filled with pure mercury and 
hermetically sealed, was placed in a vessel with a large reservoir of the usual form 
(fig. 1'), which was afterwards filled with dry oxygen. After the levels had been read, 
the silent discharge was passed until a considerable contraction was obtained. The 
corrections for changes of temperature and pressure ^vere, as in other cases, fui-nished 
by an auxiliary vessel. The free end of the siphon tube having been sealed, the pri- 
mary vessel was removed from the calorimeter, and the capsule broken by a sudden jerk. 
The breaking of the capsule, in this and other experiments, was greatly facilitated by 
introducing into the vessel a small piece of thick glass tube, which fell on the capsule 
when the vessel was shaken (fig. 1', h). 
§3. 
