IMPROVEMENTS IN MINERS' SAFETY LAMPS
Year: 1872

page_text: PROVISIONAL SPECIFICATION left by Henry Davidson Plimsoll at
the Office of the Commissioners of Patents, with his Petition, on
the 4th 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 to an improved construction of safety lamp,
in which an air or "explosion" chamber, protected by perforated
metal, is employed, as described in the Specification of Letters Patent
granted to me, and dated May 31st 1871, No. 1448, through which
chamber the air is drawn to support the flame, which is extinguished
as soon as the external atmosphere becomes of an explosive nature,
as therein described. This lamp although fulfilling the object for which
it was intended, was liable to be accidently extinguished if suddenly
moved.
According to my present Invention I provide the lamp with a wide
glass cylinder, surmounted by a narrow chimney made of a solid metal
tube, so that it will not give passage to any external currents of air to

page_text: cause a downward draught in said chimney, and to prevent the liability of
the flame becoming extinguished from the cause before referred to, I find
it necessary to supply air to the lamp above the flame as well as below, and
I accordingly provide air passages leading from the said air or explosion
chamber to the top of the glass cylinder, to conduct a current of cool
air into the lamp, near the base of the chimney, which passing down
the sides of the glass cylinder greatly assists the upward draught in
carrying off the products of combustion. As this downward draught of
air is drawn from the explosion chamber the flame will still be
extinguished, as before described, when the atmosphere surrounding
the lamp becomes explosive. I also obtain a further advantage in
preventing the tailing or tapering of the flame.
When the air is slightly charged with carburetted hydrogen (but not
sufficiently so as to be explosive) it causes the flame to elongate, and
this elongation is materially increased if there be a downward draft from
the top of the lamp chimney, the more so that in consequence of the
different densities of air and carburetted hydrogen gas there may be
a larger per-centage of the latter mixed with the external atmosphere at
the top of the lamp than there is in that surrounding the bottom of the
lamp, in fact the former may be explosive and the latter not. Now as
my downward draft in the glass cylinder is drawn direct from the
"explosion' chamber, which also supplies the upward draft for
combustion, I avoid the use of any wire gauze in a vertical position,
which is liable to give passage to an external current of air forming
a downward current in the lamp chimney, as before described. I
make the chimney of solid metal provided with a wire gauze cap
protected from external currents by the top of the lamp frame. I also
provide a vertical flange round the opening which leads from the air
chamber and surrounds the wick to prevent the contact of the flame
with the glass cylinder in the event of the lamp being overturned.
"
66
In some cases the air or explosion" chamber may be situated above
the top of the glass cylinder instead of being disposed round the oil
reservoir, as in the former case, with vertical passages to convey air
down to the annular opening which surrounds the wick tube, as before
the air being also admitted at the base of the chimney, as and for the
purpose above explained.
The air passages may be formed by making the vertical pillars of the
lamp frame tubular, and to ensure a sufficient supply of air two or

page_text: more explosion chambers may be provided, one above the other, with
perforations preferably in their top or bottom sides to avoid external
currents of air.
When the explosion chamber is situated at the base of the lamp I
prefer that the perforations, if in the external wall of said chamber,
should be made in the form of narrow slits, such as may be made by a
fine saw, to facilite cleaning out dust which may lodge therein.