A NEW OR IMPROVED SAFETY THERMOMETER OR ALARM APPARATUS FOR STEAM BOILERS AND OTHER PURPOSES
Year: 1872

page_text: PROVISIONAL SPECIFICATION left by John Clayton Mewburn at
the Office of the Commissioners of Patents, with his Petition, on
the 14th March 1872.-A communication from abroad by Jean
Theodore Fastré, of Paris, France.
I, JOHN CLAYTON MEWBURN, of 172, Fleet Street, in the City of
London, Patent Agent and Consulting Engineer, do hereby declare
the nature of the said Invention for "A NEW OR IMPROVED SAFETY
THERMOMETER OR ALARM APPARATUS FOR STEAM BOILERS AND OTHER PURPOSES,"
to be as follows:-
-
The safety thermometer or alarm apparatus which forms the subject
of this Invention is based upon the combined employment of air as
a dilating fluid under the direct action of elevations of temperature,
and of mercury as a liquid metallic vehicle which at a certain maximum
temperature covers the points of two independent platinum wires fitted
to the two electrodes of a pile. This combination connected by the
electric current to an alarum or analogous signalling device gives
warning both to the attendant and to the head of the establishment
the moment that the ambient medium reaches the maximum tempe.
rature so that the necessary measures may be taken. The apparatus is

page_text: of great advantage for steam boilers, hothouses, drying rooms, hospitals,
and other places to give warning at a distance that the maximum
temperature has been reached.
The apparatus consists of a reservoir of air terminated by a long
tube of S form containing mercury, which tube at its end unites with
a long cup or vessel containing free air. On the upper edge of this
cup is a small claw or cross piece provided with two sockets which
serve to rigidly maintain two platinum wires at the same determined
level in the cup. This level should be strictly in the same horizontal
plane as the level attained by the mercury in the cup at the time of
the maximum temperature, which is determined beforehand according
to the particular circumstances of the case. The two platinum wires
are provided at their upper end with rings to which the conducting
wires of a pile are attached. In the line of these wires an electric
alarum or signalling device is interposed which has a dial the needle of
which indicates by electrical transmission the temperature attained by
the medium.
As long as the temperature of the air reservoir and consequently of
the ambient medium does not reach the maximum limit determined
upon, and therefore as long as the level of mercury in the cup remains
below the points of the platinum wires, the current from the pile is
broken and the alarum is not made to act. But as soon as the ambient
temperature produces a dilation of the air sufficient to raise the level of
the mercury into contact with the points of the platinum wires, the
mercury being a good conductor of electricity establishes metallic con-
nection between the two wires, the electric current is produced, and the
alarum or signalling device with its dial is put into action. Immediate
warning is thus given at any required distance that the temperature has
attained its maximum limit.
In applying this aero-electric thermometer to steam boilers the air a
reservoir may be horizontal, and the S shaped tube will have one
leg or portion long enough to pass through the side of the boiler,
terminating outside in the S shape, and uniting with the cup as before
explained.