The use of the reduction-valve has made the automatic control of the
oxygen supply much simpler than in the apparatus formerly used. The
details of the connections somewhat schematically outlined are given in
fig. 32, in which D is the oxygen cylinder, K the supporting band, A the
reduction-valve, and J the tension-equalizer attached to one of the
calorimeters. Having reduced the pressure to about 2 pounds by means of
the reduction-valve, the supply of oxygen can be shut off by putting a
pinch-cock on a rubber pipe leading from the reduction-valve to the
calorimeters. Instead of using the ordinary screw pinch-cock, this
connection is closed by a spring clamp. The spring E draws on the rod
which is connected at L and pinches the rubber tube tightly. The tension
at E can be released by an electro-magnet F, which when magnetized
exercises a pull on the iron rod, extends the spring E, and
simultaneously releases the pressure on the rubber tube at L. To make
the control perfectly automatic, the apparatus shown on the top of the
tension-equalizer J is employed. A wire ring, with a wire support, is
caused to pass up through a bearing fastened to the clamp above J. As
the air inside of the whole system becomes diminished in volume and the
rubber cap J sinks, there is a point at which a metal loop dips into two
mercury cups C and C', thus closing the circuit, which causes a current
of electricity to pass through F. This releases the pressure at L,
oxygen rushes in, and the rubber bag J becomes distended. As it is
distended, it lifts the metal loop out of the cups, C and C', and the
circuit is broken. There is, therefore, an alternate opening and closing
of this circuit with a corresponding admission of oxygen. The exact
position of the rubber diaphragm can be read when desired from a pointer
on a graduated scale attached to a support holding the terminals of the
electric wires. More frequently, however, when the volume is required,
instead of filling the bag to a definite point, as shown by the
pointer, a delicate manometer is attached to the can by means of a
pet-cock and the oxygen is admitted by operating the switch B until the
desired tension is reached.
[Illustration: FIG. 32.--Part of the oxygen cylinder and connections to
tension-equalizer. At the left is shown the upper half of the oxygen
cylinder with a detail of the electro-magnet and reducing-valve. D is
the cylinder; K, the band supporting the oxygen cylinder and
electro-magnet arrangement; F, the electro-magnet; E, the tension
spring; and L, the rubber tubing at a point where it is closed by the
clamp. The tension-equalizer and the method of closing the circuit
operating it are shown at the right. C and C' are two mercury cups into
which the wire loop dips, thus closing the circuit. B is a lever used
for short-circuiting for filling the diaphragm J. G is a sulphuric-acid
container; H, the quick-throw valve for shutting off the tension
equalizer J; M, part of the ingoing air-pipe; N, a plug connecting the
electric circuit with the electro-magnet; and O, a storage battery.]
In order to provide for the maximum sensitiveness for weighing D and its
appurtenances, the electric connection is broken at the cylinder by
means of the plug N and the rubber tube is connected by a glass
connector which can be disconnected during the process of weighing.
Obviously, provision is also made that there be no leakage of air out of
the system during the weighing. The current at F is obtained by means of
a storage battery O. The apparatus has been in use for some time in the
laboratory and has proved successful in the highest degree.