THE COLLIERY GUARDIAN

AND

JOURNAL OF THE COAL AND IRON TRADES.

Vol. CVII.

FRIDAY, FEBRUARY 20, 1914.

No. 2773.

Design and Maintenance of the Miners’ Electric Lamps.

By F. J. TURQUAND, A.M.I.E.E.

From a Paper read before the Association of Mining Electrical Engineers (London Branch),

There are now on the market some dozen or so miners’
electric lamps, each with its particular merits. The
design of miners’ electric lamps may be divided into
sub-sections :—(1) The shell or case, including the
lantern or light-emitting portion ; (2) the battery or
source of electrical energy ; (3) the methods of mecha-
nically and electrically connecting the lamp case con-
taining the electric bulb with the battery, including
locking devices.

The body of the lamp may suitably be constructed of
wood, iron or steel, or aluminium alloy. Impregnated
wood has the advantage of being light, strong and not
affected by acid, but is liable to be bulky and somewhat
difficult to permanently and securely fix to the lantern.
Iron or steel is used by several makers in the form of
pressed cases. The advantages of using these metals
are—(1) interchangeability, (2) no machining, (3)
mechanical strength and rigidity, and (4) ease of manu-
facture. The disadvantages are (1) liability to rust and
acid corrosion (and of ferrous liquid getting into the
battery and ruining it), (2) weight, and (3) the difficulty

Fig. 1.—The Stach
Lamp, with Flame-
lamp Indicator.

Fig. 3.—The Varta
Miners’ Electric Lamp.

of removing a battery from a battered or dented case.
Aluminium alloys are used with success by several
manufacturers. Aluminium alloys do not rust, and acid
corrosion is not so injurious to the battery, while the
sulphates are easily and permanently removed by cold
water. A thick casting does not dent or distort as
easily as steel, and can be remelted if required. The
alloys are not, however, hard enough to provide friction
surfaces or fastenings, but brass, gunmetal, iron or steel
pieces can be cast in it and will remain tightly fixed
owing to the relative contraction of the various metals.
Battery cases should be provided with a pad of resilient
material to minimise the transmission of shock from the
case to the battery, and should also fit loose around the
battery for the same reason.

Lantern.

The usual methods employed are to mount the bulb
on spring, air, or rubber cushioned contacts, as in the
Ceag, Pape, G E.C., Stach, and B.A.C. lamps, each of
which more or less accomplishes the end in view. The

dome-shaped glasses very generally used have the
advantages of strength and of leaving only one edge to
seal against leakage. When using blown glasses of
this description, purchasers should be careful to have
thoroughly annealed glass, as only when this is properly
done can the glass be safe to use.

There are, broadly, three methods of holding the
glass dome on to the base of the lantern, viz., (1) by
pressure upon the dome; (2) a flange cast round the
base of the glass, or (3) by cementing a metallic ring
on to the edge of the glass, which ring can be screwed
or otherwise attached to the case of the lamp. When
it is thought desirable to convert the dome top into a
lens, that can be effected by either thickening the glass
in casting or blowing, or using a glass cylinder with a
lens cemented or otherwise attached to the top thereof.
It is said to be possible to obtain slightly clearer glass
in cylinder form, like the oil lamp glasses, than in the
dome shape, which is blown into a mould.

The designers of the G.E.C. lamp, having in view the
importance of obtaining the maximum of light with the

Plan of top of Battery

Plan of top of Lantern
Zoning Str itch Movement.

pi )
A!

Switch S moved to

Section csf complete lamp battery terminal

Fig. 2.—The Joel-Fors Miners’ Electric Lamp.

A = switch head. B = steel pillars. C = lantern glass.
D and E — pins for engaging in groove and lock
F = lead lock. G = hasp. H — staple. J ■= battery.
K= groove in case. L= switchpin. M - battery terminal.

minimum of shadow, effect this by securing the glass
dome, which stands on rubber, by means of an inverted
truncated cone-shaped ring fitting the dome at the
lowest part of its curve, but presenting its edge instead
of its surface to the bulb, thereby obtaining considerable
strength and a condensed light through the lens top.
In addition to the good circular illumination thus
obtained, the roof and floor can be illuminated by
inverting the lamp.

It has been proved that the current passing through
a two-volt electric bulb when broken or short-circuited
may fire methane by either the cooling lag of the fila-
ment or a make-and-break spark at the short-circuit,
and various devices are extant. The makers of the Ceag
lamp hold the bulb down on to its electric contact by a
spiral spring between the inside of the dome glass and
the top of the bulb, so that when the spring is displaced
by the moving or breaking of the dome the bulb rises
from the contact springs. In the G.E.C. lamp this
difficulty is overcome by fixing the outer glass itself in
such a way that displacement or breakage releases a
contact pin in a gastight chamber on the centre
terminal of the battery instantaneously. This arrange-

ment is really rather more sensitive, and is a perfectly
safe break in a gaseous mixture, even if the outer
glass itself is not hermetically sealed. Other designers
so arrange that the chamber formed by the outer glass
shall be more or less filled with compressed air or other
gas that will rush out immediately the hermetic seal is
broken, as well as' open the electrical circuit. This
method, although perhaps more difficult to maintain in
its completeness, has the added advantage of temporarily
preventing (by an outgoing draft of air) ingress of the
outer atmosphere, and of prolonging the interval
between the displacement or fracture of the outer glass
and the actual inrush of gas upon the bulb, intact or
broken.

Switch.

The simpler and smaller the switch between the bulb
and the battery the better. The type that appears to

Top View

Fig. 4.—The T.K. Miners’ Electric Lamp,
by the General Electric Company.

A — Osram bulb. B = rotating baseplate, raising and
lowering bulb holder on to battery contact, and free to
rise off inner battery contact if glass is broken or dis-
placed. 0 = rubber compression ring. D = locking
screw (dotted lines show position when ready for
removing top). E = rubber ring gripping bottom case
and battery. F = steel plate in position. G = lead
sealing rivet. H = steel pillars, one pair fitting into
recesses and the other pair fastened by nuts. I — rubber
sealing cushion of switch chamber. J = celluloid sleeves.
K = inner battery terminal. L = resilient pad upon
which battery rests. M =- head of lead sealing rivet.

have found most favour is simply a screw, the head of
which is outside and the point inside a flame-proof
chamber. Screwing down on to a contact closes the
circuit, and it really seems difficult to improve on the
idea. Another class of switch where the lamp-top turns
upon the battery outer case, however, is as effective and
a somewhat easier form to manipulate when the fingers
are large or cold. To avoid accidental sparking outside
the lamp, in designing the switch it is important that
the external portion, if of metal, shall be permanently
connected to the outer case of the lamp if the case is
utilised as a conductor, but insulated from it if the case
is not so used.

Primary Battery.

The makers of nearly every portable lamp battery
with which the writer is acquainted, employ metallic
zinc as the anode or soluble electrode and carbon as the
cathode, with chromic acid as the depolarising chemical,
either free or in combination with its own or other salts
dissolved in the electrolyte.

Each manufacturer has his own method of separating
the electrodes, one using perforated celluloid, another