IMPROVEMENTS IN CAPS OR APPARATUS FOR EXPLODING DYNAMITE
Year: 1878

page_text: LETTERS PATENT to John Henry Johnson, of 47, Lincoln's Inn Fields, in the
County of Middlesex, Gentleman, for the Invention of "IMPROVEMENTS IN
CAPS OR APPARATUS FOR EXPLODING DYNAMITE." A communication from
abroad by Friedrich Wittenberg, of Duisburg, in the Empire of Germany,
Manufacturer.
Sealed the 16th July 1878, and dated the 31st January 1878.
PROVISIONAL SPECIFICATION left by the said John Henry Johnson at the
Office of the Commissioners of Patents on the 31st January 1878.
JOHN HENRY JOHNSON, of 47, Lincoln's Inn Fields, in the County of Middlesex,
Gentleman. "IMPROVEMENTS IN CAPS OR APPARATUS FOR EXPLODING DYNA-
MITE."
A communication from abroad by Friedrich Wittenberg, of Duisburg, in
the Empire of Germany, Manufacturer.
This Invention relates to caps or apparatus for exploding dynamite for blasting
purposes, and it consists in the employment of an inner cup or tube with a per-
forated bottom or end, inserted and fixed in an inverted. position, that is to say,
with the bottom or closed end upwards in an external cup or tube to which the
fuse is attached. The explosive or priming is situate between the bottoms or closed
ends of the outer and inner tubes surrounded with a metal casing on all sides, and
communicating with the cylindrical part of the outer tube only through a very
small orifice which acts as a touch hole for igniting the explosive material contained
in the interior.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said John Henry Johnson in the Great Seal Patent Office on the 17th
July 1878.
JOHN HENRY JOHNSON, of 47, Lincoln's Inn Fields, in the County of Middlesex,
Gentleman. "IMPROVEMENTS IN CAPS OR APPARATUS FOR EXPLODING DYNA-
MITE. A communication from abroad by Friedrich Wittenberg, of Duisburg, in
the Empire of Germany, Manufacturer.
"
The said Invention relates to caps or apparatus for exploding dynamite for
blasting purposes, and it consists in the employment of an inner cup or tube with
a perforated bottom or end inserted and fixed in an inverted position, that is to say,
with the bottom upwards, in an external cup or tube to which the fuse is attached.
The explosive charge or priming is situate between the bottoms of the outer and
inner tubes, surrounded with a metal casing on all sides, and communicating
with the cylindrical part of the outer tube only through a very small orifice
which acts as a touch hole for igniting the explosive material contained in the
interior.
The caps hitherto employed in blasting by dynamite consist of an open copper
cup or tube into which is pressed a certain quantity of an explosive compound,
usually a mixture of fulminate of mercury, chlorate of potash, and an adhesive
material.
If the charge of a cap is reduced below the usual minimum there is danger of
the gas resulting from the combustion escaping at the open end of the cap, as it
easily overcomes the slight resistance offered by the fuse. The cap in this case
misses fire.
In order to obviate all liability of the cap missing fire it is necessary to adopt an
arrangement by which an equally strong resistance is opposed to the charge on the
side of the fuse as on the other sides, and this result is obtained by the use of the
improved cap which forms the subject of the said Invention.
And in order that the said Invention may be fully understood I shall now pro-
ceed more particularly to describe the same, and for that purpose shall refer to the
several Figures on the annexed Sheet of Drawings, the same letters of reference
indicating corresponding parts in all the Figures.
Figure 1 of the Drawings represents an elevation of a finished cap constructed
according to the said Invention; Figure 2 is a vertical section of the same; and
Figure 3 is a corresponding horizontal section taken along the line 1, 2, Figure 2.
Figures 4 and 5 are vertical sections of the two parts of which the improved cap
is composed, shewn separate or detached.
The cap consists of two cylindrical copper tubes or cups A (Figure 4), and B
(Fig. 5), fitted the one within the other, videlicet, an inner tube A, containing the
charge M, and an outer tube B, which supports the inner tube and serves to receive
the fuse, being, say, about twice the length of the said inner tube. Both tubes or cups
may be made in the ordinary manner by means of dies or stamps from a disc of
copper, the metal forming the ends of both being allowed to retain its original
thickness, whilst the cylindrical sides are drawn out as thin as the ductility of the
copper will admit of.
The external diameter of the inner tube A corresponds to the internal diameter
of the outer tube B, so that the cylindrical sides of the two tubes fit one within
the other, as shewn in Figure 2. In making the cup or tube A, a circular hole S of,
say, about inch in diameter, is punched in or formed in the centre of its end A¹,
and serves as a touch hole for igniting the charge.
The sides of the outer cup or tube B are made thicker near the bottom or closed
end B¹, so that the internal space from P to Q (Figure 5), extending for, say, about
7/ths of the length from the open end is of cylindrical form, whilst the remaining
space near the bottom or closed end B¹, videlicet, from Q to R, forms a frustum of a
The cap is then prepared in the following manner :-The tube A is placed on
cone.

page_text: a stand which closes the hole S in the bottom A', whilst it receives from a charging
machine its due charge of inflammable material, which is then pressed in so that
the tube is filled, to, say, about two-thirds of its height from the bottom, as shewn
at M. This tube A, with its charge M, is then introduced into the open end of the
tube B, with its open end towards the bottom B₁ of the latter tube, the bottoms
A', B', of the two tubes being thus situate in opposite directions. The inner tube
A is then slid along inside the outer tnbe B to the end of the cylindrical space at
Q, Figure 5, where it is stopped by the reduced diameter. It is then forced down
to the bottom of the outer tube B by means of a vertical press worked by hand,
which presses it into a sufficient distance and jams the thin cylindrical sides into
the reduced conical space at the bottom of the outer tube B. The hand press is
combined with mechanism which comes into operation as soon as the inner tube
has assumed its proper position within the outer tube B.
•
This mechanism (which may be of any ordinary description, and to which no
claim is made) consists of horizontal punches which forin four or any suitable
number of indentations, w, w, in a row, but in close proximity, around the circum-
ference of the external tube in contact with the bottom A' of the inner tube so as
to secure it firmly in position, and the cap is now complete. It will be seen from
an inspection of Figure 2 that the inflammable material is only exposed on the
small area of the touch hole S, and is enclosed by a thick copper case on every
side. This cap may be employed for blasting purposes in the ordinary manner.
The end of the fuse is inserted in the open end of the cap which fits over it, so
that the pinching on of the same with nippers is rendered unnecessary.
On
igniting the fuse the fire obtains access to the inflammable material through the
touch hole S, and the large volume of gas suddenly generated by its combustion
inecting with resistance in every direction is only liberated by the destruction of the
casing surrounding it. Caps constructed on this principle are not liable to miss
fire even when the charge is reduced considerably below the minimum quantity
allowed for open caps.
Having now described and particularly ascertained the nature of the said Inven-
tion, and the manner in which the same is or may be used or carried into effect, I
would observe in conclusion that what I consider to be novel and original, and
therefore claim as the Invention secured to me by the herein-before in part recited
Letters Patent is, the cap for exploding dynamite for blasting purposes, consisting
of an inner cup or tube with a perforated bottom or end inserted and fixed in an
inverted position, that is to say, with the bottom upwards, in an outer cup or tube,
the explosive material or priming situate between the bottoins of the outer and
inner tubes, being surrounded with a metal casing on all sides, and communicating
with the cylindrical part of the outer tube only through a restricted orifice, which
acts as a touch hole for igniting the explosive material contained in the interior,
substantially as herein-before described.
In witness whereof, I, the said John Henry Johnson, have to this my
Specification set my hand and seal, the Third day of July, One thousand
eight hundred and seventy-eight.
J. HENRY JOHNSON. (L.S.)