112 TECHNOLOGY. 
be driven firmer and firmer until the hole is entirely closed to the top. The 
priming-rod is smeared with tallow, and often turned round during the 
charging, that it may be easily drawn out. When this is done the train is 
laid to ignite the powder in the cartridge. The most common modes of 
igniting the powder are the following. First, by using little tubes of elder 
straw, &c., filled with fine gunpowder, or brandy and powder, and con- 
nected with the cartridge by being placed in the hole left by the priming- 
rod, or inserted at first instead of the priming-rod ; second, by matches of 
rushes, or shavings, or small paper caps covered with powder and stuck into 
the hole made by the priming-rod. The fire is communicated to them by 
the sulphur wick, or a thread prepared by dipping it in sulphur. The slow 
match of sulphur allows the workman time to escape from the blast. In 
modern times the Beckford safety match is used to great advantage. The 
electric spark has proved a very safe and suitable means of igniting the 
charge, especially when a number of charges were to be ignited at the same 
time. In this way, in the year 1844, in constructing the London and Dover 
railroad, a part of the Shakspeare cliff was blasted off and thrown into the 
sea. A good mode of placing the powder at the bottom of the hole is to 
use the double cartridge of Chenhall. This apparatus (pl. 23, jig. 11 @)) 
consists of a copper tube about two feet long and of a smaller exterior 
diameter than the drilled hole, in which a small piston moves with a 
graduated rod. The piston is drawn back far enough to allow the requisite 
space for the charge of powder, which is poured into it, and then the tube 
is stopped up with a paper plug; it is then put into the drilled hole, and by 
pressure upon the piston-rod the charge is forced out of the tube, which 
is then withdrawn and the hole is filled in as usual. This method of. 
charging can only be used where the descent is directly down. 
The blasting must be so conducted that the axis of the hole drilled shall 
be parallel with the nearest open side. The surface of the fracture usually 
runs through the axis of the drilled hole. For example, if one wishes to 
blast a mass of rock having the profileaBconp (pl. 28, jig. 10), a suc 
cession of oblique drilled holes will be far more effective than perpendicu- 
lar ones. | 
Where the rock is full of moisture, cartridges of tarred linen, or paper. 
cartridges surrounded with tinfoil, and Beckford’s matches, are very useful. 
A mode of filling a drilled hole when the rock is full of moisture, which is 
employed in Sweden, is represented in jig. 8. The ordinary filling is. 
replaced by two wedge-shaped pieces of iron. ach of these pieces of iron 
ends in a smooth circular face, of a diameter somewhat less than that of the 
tin canister which serves for the reception of the powder. The charge of 
powder used is fastened by a cord on the bottom of the first wedge. The 
second wedge lies with its inclined plane on the first, and is furnished with 
an iron rod which projects from the upper opening of the tin canister. 
In the surfaces of the wedges in contact, there is a channel which reaches 
to the powder and extends into the tube of a hollow wooden staff which is 
affixed to the end of the iron rod, after a train of powder has been laid in 
the channel. cis the match affixed to the end of the train ; B and © are 
692 
