OF GASES AT CONSTANT VOLUME. 
965 
ether, alcohol, or acetone, as the case may be, is contained. In a few minutes the 
steam current raises this to boiling. Ice is placed in the condenser, and the boiling 
urged till the back-streaming of the condensed vapour is visible in the glass tubes 
leading to the condenser. The burner beneath the boiler and finally the discharge 
valve upon it are now adjusted, till the streaming in the tubes progresses at a slow 
rate. At the expiration of 40 minutes or thereabouts, the thermometer in the inner 
chamber rises to a temperature but little below the B.P. of the liquid in use. The 
final stationary temperature is not attained, however, till one-and-a-half or two hours 
have elapsed, generally. The balance above is now set vibrating for ten or fifteen 
minutes and all is ready for admitting steam. At this stage the balance probably 
shows a slight want of equilibrium due to distension under the increased pressure of 
the active sphere and also, perhaps, to some leakage of vapour into the inner chamber. 
This loss of equilibrium is, however, not attended to, the reference-state of equili¬ 
brium being taken as the state at air temperature. 
Steam is got up in the large boiler feeding the calorimeter while the balance is 
vibrating, and when the boiler has been vigorously steaming for some minutes the 
balance is brought to rest, the thermometer withdrawn from the calorimeter, and one 
for reading steam temperatures inserted in its stead. The air-escape tubulure of the 
calorimeter being uncorked, the cork stopper closing the large steam entrance at the 
back is withdrawn, and the steam pipe rocked across into its place, so that steam pours 
rapidly into the calorimeter. The steam current almost immediately appears flowing 
out through the air-escape tubulure, and this current is now moderated by inserting the 
narrow leading tube. The steam supply to the vaporizer is next to be cut otf, and 
the switch moved to put on the current in the spirals. All these operations only take 
a few seconds, and are almost automatically performed, after some training, by the 
experimenter ; so that some thirty seconds after steam is turned into the calorimeter he 
can already be observing the behaviour of the balance. Two minutes to two-and-a- 
half minutes will complete the heating of the vessels and gas, but the even swinging 
of the balance is observed till the completion of the fifth minute. Then all is to be 
again cooled as quickly as possible, for the pressure attained in some cases is so high 
and so sudden (possibly rising from 47 to 102 atmospheres in the space of a minute 
or less), that it is desirable to relieve the sphere of the excessive stress as soon as 
possible. The drying of the calorimeter should be efiected while it is still hot. 
As may be imagined, it is difficult to effect more than one experiment in the course 
of a day, and thus the completion of many series of experiments demands much time 
and labour. But except a more expeditious method of altering the initial temperature 
is devised the delay seems unavoidable. 
It will be apparent that the weighings are two in number for each experiment. 
The first gives the equilibration of the vessels when in air at known temperature and 
pressure. The second when in steam at known temperature and pressure, and when 
a certain weight of steam has been precipitated upon each. These weighings are 
