APPENDIX A

305

means of the needle valve D. The valve E is convenient in locat-
ing leaks in the apparatus, etc., but is not often used. The valve
G is a direct connection to air which is also seldom used.

The pressure regulator consists of five brass tubes 6 cm. in
diameter which are filled with water let in at K, the valves 0',
0" etc. being open and the valve N closed. When the water
begins to overflow at M into the drain pipe, the water is shut off

FIG. 92.—Diagram of viscometer set-up with multiple tube water stabilizer.
at K, and as soon as equilibrium is reached, the drain pipe is also
closed off at Z and the valves 0', 0", etc. are closed.
By allowing air to pass very slowly through the valve D the air
will be gradually forced down the tube Hf until it bubbles out
through the water, and, if the pet-cock J' is open, into the air.
If the stream of air is very slow, say a bubble or two per second,
it is evident that the pressure will be constant. If a higher pres-
sure is desired the pet-cock J' is closed when the pressure becomes
the sum of the pressures obtained by the two tubes separately
and so on for the five different pressures up to the maximum
capacity of the regulator. In lowering the pressure one must
be careful to turn the pet-cocks to air in the reverse order Jv
jiv jm an(j ju jri jn or(jer that the air under pressure may not
cause the water to be drawn back into the system. The advan-
20