340 History of Mechanical Inventions and 



small hole drilled up through the centre of it, sufficient to admit the stem 

 of a glass ball, as will be better understood by the outline, Plate VI. Fig. 1. 

 This glass ball, which is exactly the same with common crackers that 

 are stuck into the candles and explode by the water being converted into 

 steam by the heat of the flame, but instead of water, it is filled with sul- 

 phuric acid, which, on being crushed, the acid immediately comes in con- 

 tact with a detonating powder, which fires the lower part of the column 

 of gunpowder, and the full effect is given to its expansive power at the part 

 where it is wanted to exert its force. 



This detonating powder is composed of equal parts of gunpowder and 

 oxymuriate of potass, carefully mixed together with a small quantity of 

 water. To those who are not acquainted with such a mixture, it may be 

 proper to mention, that, if the two articles are mixed together in the dry 

 state, and rubbed down into a powder in any way, the whole will explode, 

 unless water be added so as to make it into a kind of paste, after which it 

 is to be spread out on some paper or cloth, and left to dry, after which it 

 easily crumbles down between the fingers into a fine powder, which should 

 be kept in a bottle, as it is easier set fire to than gunpowder. 



When this powder or priming is to be used, the tube with its ramrod 

 is to be placed into the bore down to the bottom, that is, as far as the gun- 

 powder goes ; then the powder is put in as usual, and the whole process 

 completed in the ordinary way, by hammering down clay, or broken tiles, 

 or bricks, with this great difference that the pricker (as the workman term 

 it) acquires no movement, for it is by it that almost all the accidents hap- 

 pen in our quarries. Now, in this case, the tube remains firm in its place, 

 and does not require to be moved at all, but the ramrod can be moved or 

 withdrawn at pleasure. When this is done, a small quantity (a tea-spoon- 

 ful) of the detonating powder is to be poured into the tube, after which 

 one of the glass globes is to be fixed into the end of the ramrod, and is 

 gradually lowered down into the tube till it come in contact with the pow- 

 der, after which all is now ready for the explosion ; and this is effected by 

 a simple blow, such as is produced by the hammer of a gun lock, whereby 

 the glass ball is broken. The sulphuric acid instantly lays hold of the po- 

 tass, and the chlorine is set at liberty to act on the charcoal and sulphur of 

 which the gunpowder is composed, whereby inflammation is instantly 

 produced, and the charge set on fire from the bottom. 



This part of the plan, as is before hinted, I have never actually put in 

 practice ; it has only been done with a model, but there is no doubt what- 

 ever of its answering the purpose for which it is intended. The second 

 part of the plan is to take advantage of the explosive or repulsive power 

 of the charge, by calling to our aid one of the mechanic powers, so as to 

 divide the rock at the bottom of the bore. Now, this is to be done in a 

 very effectual manner by means of the wedge. In order, however, to ef- 

 fect this, the bore must be somewhat different from the common. After 

 having been carried to the depth which the workman judges proper for 

 his present purpose, another bore must be carried down 18 inches or two 

 feet, of less than half the diameter of the original bore, and this will be 



