AN IMPROVEMENT IN SAFETY LAMPS
Year: 1871

page_text: LETTERS PATENT to Henry Davidson Plimsoll, of Gordon Square, in
the County of Middlesex, for the Invention of "AN IMPROVEMENT IN
SAFETY LAMPS."
Sealed the 21st November 1871, and dated the 31st May 1871.
PROVISIONAL SPECIFICATION left by the said Henry Davidson
Plimsoll at the Office of the Commissioners of Patents, with his
Petition, on the 31st May 1871.
I, HENRY DAVIDSON PLIMSOLL, of Gordon Square, in the County of
Middlesex, do hereby declare the nature of the said Invention for "AN
IMPROVEMENT IN SAFETY LAMPS," to be as follows:-
My Invention consists in so constructing a safety lamp that the light
will be instantaneously extinguished when exposed to an explosive
atmosphere.
I construct the body of the lamp with an internal air chamber or
passage through which the air is supplied to support the flame. This

page_text: may
air chamber communicates with the external atmosphere by an opening,
which is protected by wire gauze or a perforated metal plate, such as is
usually employed in safety lamps, and the air chamber surround
the wick, so that the incoming current of air will converge on the flame.
Thus whenever the air from which this current is drawn becomes
explosive the air current will be ignited by the flame and will explode
within the air chamber or passage, and cause the instant extinction of
the light. The explosion is prevented by the wire gauze or perforated
metal from communicating with the external atmosphere.
SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said Henry Davidson Plimsoll in the Great Seal Patent
Office on the 30th November 1871.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, HENRY
DAVIDSON PLIMSOLL, of Gordon Square, in the County of Middlesex,
send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Thirty-first day of May, in the year
of our Lord One thousand eight hundred and seventy-one, in the thirty-
fourth year of Her reign, did, for Herself, Her heirs and successors,
give and grant unto me, the said Henry Davidson Plimsoll, Her special
licence that I, the said Henry Davidson Plimsoll, my executors, adminis-
trators, and assigns, or such others as I, the said Henry Davidson
Plimsoll, my executors, administrators, and assigns, should at any time
agree with, and no others, from time to time and at all times thereafter
during the term therein expressed, should and lawfully might make,
use, exercise, and vend, within the United Kingdom of Great Britain
and Ireland, the Channel Islands, and Isle of Man, an Invention for
"AN IMPROVEMENT IN SAFETY LAMPS," upon the condition (amongst others)
that I, the said Henry Davidson Plimsoll, my executors or adminis-
trators, by an instrument in writing under my, or their, or one of their
hands and seals, should particularly describe and ascertain the nature of
the said Invention, and in what manner the same was to be performed,
and cause the same to be filed in the Great Seal Patent Office within
six calendar months next and immediately after the date of the said
Letters Patent.

page_text: NOW KNOW YE, that I, the said Henry Davidson Plimsoll, do hereby
declare the nature of my said Invention, and in what manner the same
is to be performed, to be particularly described and ascertained in and
by the following statement, reference being had to the accompanying
Drawing hereunto annexed, and to the letters and figures marked thereon
(that is to say) :-
Safety lamps as usually constructed are sometimes liable to have
their safety properties overcome when suddenly exposed to a current
or atmosphere of inflammable gases or firedamp, and my Invention is
designed to prevent the communication of flame to the atmosphere
surrounding the lamp, and thereby avoid all risk of accidents in coal
mining from this cause.
My Invention consists in so constructing a safety lamp that the light
will be instantaneously extinguished when the lamp is surrounded by an
explosive atmosphere.
I construct the body of the lamp with an internal air chamber or
passage through which the air is supplied to support the flame. This
air chamber communicates with the external atmosphere through wire
gauze or a perforated metal plate, such as is usually employed in safety
lamps, and the air chamber may surround the wick, so that the incoming
current of air will converge on the flame. Thus whenever the air from
which the current is drawn becomes explosive the air current will
be ignited by the flame and will explode within the air chamber or
passage, and cause the instant extinction of the light. The explosion is
prevented by the wire gauze or perforated metal from communicating
flame to the external atmosphere.
The accompanying Drawing shows (full size) a half sectional elevation
of a safety lamp constructed according to my Invention.
a is the oil receptacle, which is wholly or partly received in a cavity b
in the lower part of the casing of the safety lamp; c is the air chamber
or passage surrounding the lamp a. The walls d and e of this chamber
or passage are made of plates of sheet metal (brass) fitted together con-
centrically in the manner shown, so as to leave an annular space of
about / of an inch between them in a lamp of the size drawn, and less
for a lamp of larger diameter (as the capacity of the chamber or passage
must not be increased beyond certain limits), the said plates being
united at bottom (by soldering in the usual way) to a flange or ring f

page_text: on the inner plate d. The outer plate or wall e is made with a number
of minute perforations through which the entire supply of air required
for the combustion of the flame passes. The thickness of this plate e
would depend somewhat upon the size of the perforations, but it
must be of such thickness as to prevent the passage of flame through
the perforations when the ignition of explosive gases takes place in the
chamber c. Perforations 1/4th part of an inch in diameter in a plate
1/16th part of an inch in thickness will answer the purpose, but I do not
limit myself to these dimensions, the object being to prevent the passage
of flame without obstructing the admission of air to the lamp. The
perforations should be disposed at equal distances apart, and not too close
together, so as to leave sufficient metal to cool and destroy the flame
resulting from the ignition of explosive gases in chamber c, nor should
the perforations be more numerous than is required to admit an adequate
supply of air to feed the flame of the lamp. The top g of the chamber c
is bent into a conical form at the centre around an opening through
which the wick tube h rises, the opening being of sufficient size to
allow the air to pass freely to the flame, and allow for the free escape or
expansion when the ignition of explosive gases takes place in chamber c.
The top of the inner wall d is also similarly bent or made into a
conical form at the centre, and has a central aperture for the passage
of the wick tube h. The plate g is provided with a gallery to carry the
glass chimney i and wire gauze covering therefor, as usually employed
in some kinds of safety lamps, and to this plate 9 the ordinary rods k of
the framework are attached, as shown. The chimney i is carried up
to the top of the lamp, which is provided with the usual protecting top
of wire gauze and perforated sheet metal for the exit of the products of
combustion. The chimney i is fitted air-tight in its gallery, being
cemented therein, so that the whole of the air supply must pass through
the chamber c to the flame, thereby preventing any accumulation of
explosive gases in the upper part of the lamp.
Having described the nature of my Invention and the manner of
performing the same, I declare that what I claim as my Invention to be
protected by the herein-before in part recited Letters Patent is, con-
structing or providing safety lamps with a passage or chamber to admit
the supply of air to the flame, the said chamber or passage being so
disposed and protected by perforated metal or its equivalent that the
lamp flame will be extinguished immediately the atmosphere whence

page_text: the air supply is drawn becomes explosive, as and for the purpose
herein-before set forth and described.
In witness whereof, I, the said Henry Davidson Plimsoll, have here-
unto set my hand and seal, this Twenty-ninth day of November,
in the year of our Lord One thousand eight, hundred and seventy-
one.