IMPROVEMENTS IN MINERS' SAFETY LAMPS
Year: 1872

page_text: LETTERS PATENT to Henry Davidson Plimsoll, of Gordon Square, in
the County of Middlesex, for the Invention of "IMPROVEMENTS IN
MINERS' SAFETY LAMPS."
Sealed the 22nd April 1873, and dated the 5th November 1872.
PROVISIONAL SPECIFICATION left by the said Henry Davidson
Plimsoll, at the Office of the Commissioners of Patents, with his
Petition, on the 5th November 1872.
I, HENRY DAVIDSON PLIMSOLL, of Gordon Square, in the County of
Middlesex, do hereby declare the nature of the said Invention for
"IMPROVEMENTS IN MINERS' SAFETY LAMPS," to be as follows:-
:-
My Invention relates, 1st., to improved means of preventing the
exposure of the naked flame by withdrawing the lamp from its pro-
tecting casing whilst admitting of the removal of the oil reservoir for
refilling the same.

page_text: According to this part of my Invention I make the wick tube
independent of the oil chamber, and lock the former in the casing of the
lamp so that although the oil reservoir may be withdrawn from the
lamp, the wick tube cannot. The wick tube is fixed in a disc or plate
fitting closely in a corresponding opening in the casing, and provided
with a lock to secure it in place. This lock is provided with two or
more bolts opened by a key, to be retained in the possession of the
under viewer or other officer, as the wick tube under no circumstances
ever requires to be removed by the workmen. The key is provided with
two bits, each having a different set of wards and acting simultaneously
to open the lock, which it therefore would be a matter of considerable
difficulty to pick.
.
My Invention relates, secondly, to a means of guarding against
accidents from the fracture of the glass cylinder in lamps, such as that
known as the Clanny lamp, without greatly intercepting the light,
and consists in surrounding and enclosing the flame with a cylinder or
chimney of wire gauze of the ordinary kind placed within the glass of
the lamp, and comparitively close to the flame. I may fit this gauze
chimney on the lock plate of the wick tube above described, if the lamp
is constructed with the improvement constituting the first part of this
Invention. In this position the rays of light are obstructed to a much
less degree than when the gauze is placed at a greater distance from the
flame, outside the glass for instance. By this means all danger of
accident resulting from the fracture of the glass cylinder is removed, as
the flame will still be protected by the interior gauze cylinder.
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 5th May 1873.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, HENRY
DAVIDSON PLIMSOLL, of Gordon Square, in the County of Middlesex,
send greeting.

page_text: of our Lord One thousand eight hundred and seventy-two, in the
thirty-sixth 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, admini-
strators, 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 "IM-
PROVEMENTS IN MINERS' SAFETY LAMPS," upon the condition (amongst
others) that I, the said Henry Davidson Plimsoll, my executors or
administrators, 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.
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 Sheet of Drawings
hereunto annexed, and to the letters and figures marked thereon (that is
to say) :-
My Invention relates, 1st., to improved means of preventing the
withdrawal of the lamp from its protecting casing and the exposure of
the naked flame whilst admitting of the removal of the oil reservoir for
refilling the same.
According to this part of my Invention I make the wick tube
independent of the oil vessel, and lock the former in the main frame or
casing of the lamp, so that although the oil vessel may be withdrawn
from the lamp the wick tube cannot. The wick tube is fixed in a disc
or plate fitting closely in a corresponding opening in the casing, and
provided with a lock to secure it in place. This lock is fitted with two
or more bolts opened by a key to be retained in the possession of the
under viewer or other officer, as the wick tube under no circumstances

page_text: ever requires to be removed by the workmen. The key is provided with
two bits acting simultaneously to open the lock, which it therefore would
be a matter of considerable difficulty to pick. Moreover the shape of
the key and key hole may be made slightly different for each lamp, so
that a separate key would be required for each lamp, thus increasing
the difficulty of tampering with the lock. Each lamp and its key would
be distinguished by a corresponding number.
My Invention relates, Secondly, to a means of guarding against acci-
dents from the fracture of the glass cylinder in lamps, such as that known
as the Clanny lamp, without greatly intercepting the light, and consists in
surrounding and enclosing the flame with an inner cylinder or chimney
of wire gauze placed within the glass of the lamp, and comparatively
close to the flame. I may fit this gauze chimney on the lock plate of
the wick tube above described if the lamp is constructed with the,
improvement constituting the first part of this Invention. In this
position the rays of light are obstructed to a much less degree than when
the gauze is placed at a greater distance from the flame as in the
ordinary Davy lamp. The gauze being to some extent protected by the
outer glass cylinder I am enabled to place it much nearer to the flame
than would be safe in an ordinary Davy lamp, without however loosing the
advantage which this lamp possesses, viz., that of being a safety lamp
within a safety lamp; whereby danger of accident resulting from the
fracture of the outer glass cylinder is removed, as the flame would still
be protected by the inner gauze cylinder.
Figure 5 shows the gauze cylinder attached to the lock plate.
A is the oil vessel; B, the wick tube; and C the lock case in which
The oil vessel is screwed into the
the wick tube is securely fixed.

page_text: part D of the main framing in the usual manner, so that it may be
readily withdrawn for refilling. The wick tube is made separate from
the oil vessel and merely dips down therein through a corresponding
aperture in its top to convey the wick to the oil; it is securely locked
in the frame D, so that although the oil vessel may be withdrawn, the
wick tube cannot except by means of the proper key, and therefore the
flame cannot be exposed by the miner, as although the wick itself might
perhaps be drawn out of the wick tube, yet in so doing the flame
would inevitably be extinguished. The lock case is provided with a
projecting flange around the lower edge which is accurately fitted in a
corresponding recess in plate D, as shown. E, E', are the spring bolts
which shoot over the top of plate D on opposite sides of the lock, so that
the wick tube cannot possibly be withdrawn unless the bolts are first
drawn back by means of a key.
The internal construction of the lock is seen in Figure 3. The bolts
E, E', are made of the form shown, and slide the one over the other;
they are forced outwards by the spring F, and are bevelled at their
projecting ends so as to be pressed back in the act of inserting the wick
tube in the lamp, and each is formed with a cavity within which the
key works.
Referring to Figure 1, G is the outer cylinder of glass securely fitted
and cemented in grooves in the frame D of the lamp as shown, so that
no air can enter. The glass cylinder is surmounted by a cylinder of
perforated copper plate O through which the air enters to support the
flame. H is the inner cylinder of wire gauze of the usual description,
closed at top by wire gauze, and surmounted by a solid metal chimney I,
covered at top with perforated metal or wire gauze protected by the
dome K. The metal chimney I is supported by the lamp framing at
N, N', as shown. The inner gauze cylinder H may either be screwed
on the lock, as shown in Figure 5, or on to a perforated metal plate L
independent of the lock soldered on the inner flange which supports the
glass cylinder G, as shown. This plate also carries an inner cone M by
which the air is conducted to the flame, the course of the air being
indicated by the arrows. The object of this cone is to get the flame (in
an explosive atmosphere) back into the space beneath the perforated
metal. I find that the cold air, when it has passed through the openings
at N, descends more readily to the bottom and approaches the flame

page_text: from a lower level. By this contrivance the flame is puffed out as
described in a former Patent granted to me, and then, when the white
flame at the wick is extinguished, the top of the gauze cylinder H-being
the hottest part attracts the air entering the lamp, and the blue flame
being neglected is extinguished. By the use of the solid metal
chimney I disposed as shown, the lamp is unaffected by currents of
inflammable air, which entering the perforations in O passes across and
out at the other side without affecting the flame.
The cold air entering the opening in the lamp frame N and passing
down outside the inner cylinder buoys up the carbonic acid gas, so that
it escapes freely, not only through the gauze top of cylinder H, but that
of the metal chimney I, so that there is not only no down-draught from
the top, but the lamp will stand all necessary movement even in currents
of air without fear of the flame being extinguished by the inability of
the carbonic acid gas to escape.
The gauze cylinder H prevents the flame playing upon and over-
heating the outer glass cylinder when the lamp is in an inclined position.
P is the wick trimmer, it is fitted in a tube passing through the lock,
and is thickened at the lower part to prevent it being pushed up too far
into the lamp.
In Figure 6 the inner cylinder H is shown as of glass surmounted
by a metal cover R enclosed at top by perforated metal or wire gauze
as shown, but this I do not desire to claim as part of my present
Invention.
Having described the nature of my said Invention, and the manner in
which the same is to be performed, I declare that what I claim as my
Invention to be protected by the herein-before in part recited Letters
Patent is,―
1st. Making the wick tube independent of the oil vessel and locking
it in the lamp casing, so that although the oil vessel may be readily
removed the wick tube cannot, substantially as and for the purpose
hercin set forth.
2ndly. The combination in a safety lamp of a wire gauze cylinder, or
chimney placed within a glass cylinder, and comparatively near to

page_text: not greatly obstruct the night, while in the
event of the glass cylinder being fractured no danger will ensue, the
flame being still protected by the gauze, substantially as herein described
and shewn in the Drawings.
In witness whereof, I, the said Henry Davidson Plimsoll, have
hereunto set my hand and seal, this Thirtieth day of April, in
the year of our Lord One thousand eight hundred and seventy-
three.
SHOW awings.
In witness whereof, I, the said Henry Davidson Plimsoll, have
hereunto set my hand and seal, this Thirtieth day of April, in
the year of our Lord One thousand eight hundred and seventy-
three.
HENRY D. PLIMSOLL. (L.S.)