40 
effective results on firing the second set of shot-holes. When successive series of holes are to be fired by 
means of safety-fuse, the length of the fuses may bo regulated, if necessary, so as to effect the charge of 
certain holes earlier than that of other holes. If, also, the ends of fuses be brought together, their ignition 
may be accomplished at one and the same time. This may bo effected by enclosing the ends in a small 
powder-cartridge, and firing the latter by a short piece of safety-fuse. 
DETONATORS. 
According to the reports of the mining inspectors there is no particular pre¬ 
ference for any one description of detonator on any of the gold-fields. Senior 
Inspector Nicholas states that the eagle brand, manufactured by George Egestorff, of 
Linden, near Hanover, is pretty generally used in his district, and he adds — “No com¬ 
plaints of failure of these caps to explode have been brought under my attention during 
the past year. This may be due to the fact that when a ‘ missed fire ’ occurs, the 
cause is seldom inquired into. Whether it arises from a defect in the fuse, or from the 
coating of grease or tar not properly closing the junction of the cap and fuse, and thus 
admitting water into the cap and wetting the powder of the fuse, at any rate the 
‘missed fire’ follows, and is not troubled further about, because there is no danger 
attendant on the ‘ missed fire ’ of a dynamite charge. Another fuse with a detonator is 
simply placed in the hole and fired, after the required lapse of time. The fulminate in 
the detonator cap is waterproof.” 
On the subject of detonators, the author of British Mining remarks:— 
To the researches of Roux aud Sarrau is chiefly duo the light thrown on the possibility of producing 
two kinds of explosion in the same substance—one by the application of heat and percussion, the other by 
flame-heat. Heat and percussion are produced in an explosive by the ignition of fulminate of mercury, 
which in itself possesses a detonating quality. 
Detonation may be defined as the instantaneous decomposition of an explosive. When gunpowder 
is fired in the usual manner, combustion takes place, each grain burning from the surface inwards; but, 
when nitro-glycerine compounds are ignited by means of fulminate of mercury, the mass explodes simul¬ 
taneously or nearly so. In one case the rupturing force may be said to be gradually developed, in the other 
instantaneously produced. The following table, by Roux and Sarrau, give the relative strength of three 
well-known explosive compounds when simply fired and detonated :— 
Simple 
explosion. 
,. 1*00 
. 3-00 
4-8G 
Detonation. 
4*34 
G-46 
10-13 
Relative weight 
of gases. 
0-414 
0-850 
0-800 
force is gained by detona- 
brief consideration of the 
Gunpowder 
Gun-cotton 
Nitro-glycerine ... 
From the foregoing figures it will appear that an enormous instantaneous 
tion over the simple explosion of either of the compounds enumerated ; while a 
general facts already adverted to will suffice to show that if high speed in levels or shafts are to be obtained 
by means of boring-machines, the strongest explosives must bo employed and detonated, so as to dislodge 
the rock under all the conditions in which the bore-holes may be placed, and that it will be desirable to 
shatter the rock into fragments for effecting their immediate removal. 
Detonators are now so well known as to render any description of them unnecessary. Dynamite may 
be completely detonated by means of a treble detonator, if uniformly plastic. On the other hand, if hard, 
or if it should present a mottled appearance, a quintuple detonator may fail to effect the object of complete 
detonation. 
BORING SHOT HOLES. 
On this subject Mr. Hunt, in his valuable work already quoted from, has the 
following observations: — 
Two distinct systems for arranging the holes for blasting purposes aro in use, viz.: —1. The 
“ Circular Cut,” which includes centre or rupturing holes, surrounded by shot-holes more or less concentric 
with the rupturing holes, and angled, so as to allow the explosive to remove, first, a centre core; second, 
the rock encircling this core. 
2 . The “ Square Cut,” iu which the shot-holes are mostly parallel to the sides of a level or shaft, 
the holes being angled, so as to remove, first, the wedge; second, the rock on each side of this wedge. The 
circular cut system (devised in driving the Mount Cenis tunnel) is observed mostly on the Continent, and 
particularly in the Seraing collieries, Belgium. 
The form and character of rock-boring machines, together with the method resorted to for mounting 
them, render it necessary that the circular, the square-cut, or a combination of these two systems should be 
