o
the base by a copper screw, E. The tube C is filled to a certain
height with mercury and then petroleum. The outer ends of the five
platinum wires are soldered to ordinary copper wires and
connections made to various points on a rheostat as shown. The
diagram, Fig. 2, shows how the connections to the supply current
are made. The apparatus operates as follows: The tube is immersed
in the matter to be heated, a liquid, for instance. As

[Illustration: Wiring Diagram Showing How the Connections to a
Source of Current Supply are Made]

the temperature of this rises, the air expands and exerts pressure
on the petroleum in the tube C so that the level of the mercury is
lowered. The current is thus compelled, as the platinum wires with
the fall of the mercury are brought out of circuit, to pass
through an increasing resistance, until, if necessary, the flow is
entirely stopped when the mercury falls below the wire 5.

With this very simple apparatus the temperature can be kept
constant within a 10-deg. limit, and it can be made much more
sensitive by increasing the number of platinum wires and placing
them closer together, and by filling the tube A with some very
volatile substance, such as ether, for instance. The petroleum
above the mercury prevents sparking between the platinum wire and
the mercury when the latter falls below anyone of them.

** Repairing a Washer on a Flush Valve [344]

When the rubber washer on the copper flush valve of a soil-basin
tank becomes loose it can be set by pouring a small quantity of
paraffin between the rubber and the copper while the valve is
inverted, care being taken to have the rubber ring centered. This
makes

[Illustration: Flush Valve]

a repair that will not allow a drop ot water to leak out of the
tank.
--Contributed by Frank Jermin, Alpena, Michigan.

** Cleaning Discolored Silver [344]

A very quick way to clean silver when it is not tarnished, but
merely discolored, is to wash the articles in a weak solution of
ammonia water. This removes the black stains caused by sulphur in
the air. After cleaning them with the solution, they should be
washed and polished in magnesia powder or with a cloth. This
method works well on silver spoons tarnished by eggs and can be
used every day while other methods require much time and,
therefore, cannot be used so often.

** How to Make a Small Electric Motor [345]
By W. A. ROBERTSON

The field frame of the motor, Fig