ON AEGON AND ITS COMPANIONS. 
77 
conimunicating through the stop-cock 1) with the 
pump, on the one hand, and througli E with the 
inverted siphon on the other. The point of the 
siphon was sealed at F, and drawn out to a fine 
point which was scratched, so that the end could l)e 
easily ])roken by pressing down on it tlie inverted 
gas-tube containing the gas under experiment. By 
raising the reservoir G, mercury entered the appa¬ 
ratus to above the level of the india-rubber tube. 
The clip K on the india-rubber connecting-tTd)e was 
then closed. The whole apparatus was then evacu¬ 
ated with the pump, until no bubbles were carried 
over, an operation lasting half-an-hour. The stop¬ 
cocks 1), E, and L being shut, the point of the capil¬ 
lary siphon was broken by pressing on it witli the 
inverted test-tube at E, and gas entered the space 
comprised between the stop-cocks D, E, and L. The 
stop-cock L was then opened ; the gas entered the 
apparatus, and “ washed it out,” diluting the resi¬ 
dual air (of whicli there was only the minutest tince, 
seeing that an almost complete vacuum had been 
established by the Topler’s pump) ; and this gas was 
pumped out, and in the case of the rarer gases, 
collected and preserved. The main body of gas was 
then admitted by closing D and opening E ; and the 
clij) K on the rubber tube was the]i opened, the 
mercury reservoir G being temporarily lowered, (tn 
raising it again, mercury fell in the reservoir until 
it took its level in the capillary part opposite B, 
while the mercury in the volume-tube stood at H. 
This capillary part of the volume-tube was made of 
tubing of the same bore as the lower capillary of 
the reservoir G, so as to avoid errors due to the 
capillarity of mercury. The temperature and the 
relative positions on the scale of the levels of the 
mercury in the capillary tubes and the barometer 
were then read. The reservoir M was next filled 
with mercury, and pushed up, until the capillary 
constriction of the volume-tube at B was well 
covered. The volume-tube was then bent over, and 
broken at the capillary B ; mercury entered, and 
Fig. 7. 
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