s
coupled to the sodium-bicarbonate can. It is seen that this last
connection is the only one not tested, and it has been found that care
must be taken to use only the best gaskets at this point, as frequently
leaks occur; in fact, it is our custom to moisten this connection with
soapsuds. If new rubber gaskets are used a leak is never found.

SUPPLEMENTAL APPARATUS.

To maintain the apparent volume of air through the whole system
constant, oxygen is admitted into the tension-equalizer until the same
tension is exerted on this part of the system at the end as at the
beginning. This is done by closing the valve connecting the
tension-equalizer with the system and admitting oxygen to the
tension-equalizer until the petroleum manometer shows a definite
tension. After the motor is stopped, at the end of the experimental
period, there is a small amount of air compressed in the blower which
almost instantly leaks back through the blower and the whole system
comes under atmospheric pressure, save that portion which is sealed off
between the two levels of the sulphuric acid in the two absorbing
vessels. A few seconds after the motor is stopped the valve cutting off
the tension-equalizer from the rest of the system is closed, the
pet-cock connecting this with the petroleum manometer is opened, and
oxygen is admitted by short-circuiting the electrical connections at the
two mercury cups. This is done by the hands of the observer and must be
performed very gently and carefully, as otherwise oxygen will rush in so
rapidly as to cause excessive tension. As the bag fills with gas, the
index on the petroleum manometer moves along the arc of a circle and
gradually reaches the desired point. At this point, the supply of oxygen
is cut off, the valve connecting the tension-equalizer with the main
system is opened, and simultaneously the needle-valve on the
reduction-valve of the oxygen cylinder is tightly closed, preliminary to
weighing the cylinder. At this point the motor can be started and the
experiment continued.

It is necessary, then, that the oxygen cylinder be weighed. This is done
after first closing the pet-cock on the end of the pipe conducting the
gas beneath the floor of the calorimeter room, slipping the glass joint
in the rubber pipe leading from the reduction valve to the pet-cock, and
breaking the connections between the two rubber pipes, the one from the
pet-cock and the other to the reduction valve, also breaking