104                                          THE  TECHNOGRAPH.

THE NEW MERCURY COLUMN AT THE UNIVERSITY OF

ILLINOIS.                           '
 

By Chas. H. Trego, '94, School of Elecrical Engineering.
 

Two objects were in view in impraving the mercury column as
described below. First, to substitute for the slow and irregular
action of the hand pump, some automatic means for producing a con¬
tinuous and easily regulated pressure. Second, to provide an attach¬
ment for testing steam engine indicators by direct steam pressure
measured by the mercury column. Both these ends have been ac¬
complished with entire success, a very rapid, or an exceedingly gradual
rise in pressure up to 200 pounds can be automatically obtained with
perfect ease, and the indicator attachments are found to be in every
way an improvement on the means commonly used. The apparatus was
designed by Professor Scribner, and has been constructed under his
supervision.

In using it the weight of a column of mercury is balanced against
the elasticity of the spring of the steam gauge or indicator, and the
pressure thus acting on the spring, is computed from the measured
height of the mercury.

Pressure can be applied by the small hand pump, which
forces oil in through the pipe X; also by steam through the pipe Z, or
by the hydraulic apparatus shown at C, the working of which will
be described later. In whichever way the pressure is applied, oil is
forced through the pipe L into the cylinder D. The lower part of this
cylinder contains mercury, which the oil forces out through the pipe
M into the glass tubes TT forming the column. The height to which
the mercury rises depends upon the pressure applied to the oil. The
tubes TT are made of heavy glass, in six foot lengths, and behind them
is a scale divided into inches and running the full length of the tubes.
The joints in the tubes are at different levels, so that the height of the
mercury can always be read in one tube when it is hidden by the joint in
the other. To find the pressure due to the mercury, its height in inches
above the zero mark, is multiplied by the weight of a cubic inch of
mercury at the observed temperature. This gives the pressure in
pounds per square inch. The weight of a cubic inch of mercury at
60° F. is 0.4 911 74 pounds.

The gauges to be tested are screwed to cocks on the pipe R.
This pipe is connected to the vertical pipe R^, which runs downward
and connects to the pipe M containg mercury underpressure; a glass