mping may possibly be saved by making use of a water pump.

The tube to be exhausted is washed and dried by careful heating over a
Bunsen burner and by the passage of a current of air. The exhausting
tube is then drawn down preparatory to sealing off, and the apparatus
placed upon the pump. It is best held in position by a wooden clamp
supported by a long retort stand.

Exhaustion may proceed till the mercury in the fall tubes commences to
hammer. At this point the tube must be carefully heated by a Bunsen
flame, the temperature being brought up to, say, 400 deg. C. The heating
may be continued intermittently till little or no effect due to the
heating is discernible at the pump. When this stage is reached, or
even before, the electrodes may be connected up to the coil and a
discharge sent through the tube.

Care must be taken to stop the discharge as soon as a purple glow
begins to appear, because when this happens, the resistance of the
tube is very low, the electrodes get very hot, and may easily get
damaged by a powerful discharge, and the platinum of the anode (if a
focus tube is in question) begins to be distilled on to the glass.
The heating and sparking are to be continued till the resistance of
the tube sharply increases. This is tested by always having a spark
gap, conveniently formed by the coil terminals, in parallel with the
tube. If the terminals are points, it is convenient to set them at
about one quarter of an inch distance apart.

As soon as sparks begin to pass between the terminals of the spark gap
it becomes necessary to watch the process of exhaustion very
carefully. In the first place, stop the pump, but let the coil run,
and note whether the sparks continue to flow over the terminals. If
the glass and electrodes are getting gas free, the discharge will
continue to pass by the spark gap, but if gas is still being freely
given off, then in perhaps three minutes the discharge will return to
the tube, and pumping must be recommenced. The Roentgen effect only
begins to appear when the tube has got to so high a state of
exhaustion that the resistance increases rapidly.

By pumping and sparking, the resistance of the tube may be gradually
raised till the spark would rather jump over 2 inches of air than go
through the tube. When this state is attained the Roentgen effect as
tested by a screen of calcium tungstate should be very brilliant. No
conclusion as to the equivalent resistance o