History of Mechanical Inventions, 4c. 339 



Art. XXVII.— HISTORY OF MECHANICAL INVENTIONS 

 AND PROCESSES IN THE USEFUL ARTS. 



1. Account of a Cheap and Effectual Method of Blasting Granite Rock. 

 By William Dyce, M. D. F. R. S. Ed. Communicated by the Author. 



The city of Aberdeen is particularly favourable, in point of situation, for 

 the exportation of granite ; and, as it is well known that this mineral 

 abounds in an especial manner in and about it, it is no wonder if the in- 

 habitants avail themselves of every opportunity of supplying their neigh- 

 bours wherever a market can be found. The quality of this granite has 

 been universally allowed to be superior to any that has yet been discover- 

 ed, not only in point of beauty of colour, but in durability and tenacity 

 of parts, so as to resist the greatest weight that can almost be put upon it, 

 whereas all other granites are crushed by their own superincumbent weight 

 where they exceed 200 feet in altitude. This tenacity of its composition 

 renders it valuable for many purposes, and its superiority for street pave- 

 ment does not require to be pointed out; independent of its great use in 

 the construction of arches in bridge work, and in the simple article of a 

 fire-proof press or repository for books or papers, which I believe was 

 never yet known to be injured by fire in a house. 



But whatever may be the qualities of this substance, that is not the pur- 

 port of my present communication. What I have in view is, to detail a 

 method whereby it can be more effectually detached from its solid bed. 



I have for many years suspected that the plan usually adopted was 

 wrong, that of igniting, from three to ten feet of gunpowder, at the top 

 of a tube whose diameter did not exceed one to two inches at most. I 

 conceive that this mode of igniting the powder, gives the greatest power 

 to the weakest part, for the clay, or material with which the whole is to 

 be compressed, is by no means equal to the resistance of the solid block 

 consequently, it will give way first, and the advantage of the explosive 

 power of the gunpowder will be imparted to the upper side of the block 

 and very little to the lower, so that a few splinters will be thrown off, 

 without one particle being detached below the centre of the gunpowder. 

 It is this circumstance that emboldens me to speak, having observed it 

 on several occasions ; and although I cannot prove from actual experience 

 what 1 have to recommend, yet the thing seems plausible ; at all events it 

 will answer the purpose of igniting the powder at the bottom of the charge, 

 and that with more certainty and safety than is done by any of the me- 

 thods that arc at present followed. 



It is to be done in this manner. According to the depth of the bore, a 

 copper tube is to be made, so as to reach to the bottom, of the diameter 

 of a quarter to half an inch. This tube is then to be provided with an iron 

 rod, or, if the bore is of great depth, it would require to be made of steel 

 in case of bending, but in either way it must be made of such size as will 

 move easily up and down in the tube ; and the lower part of this rod (per- 

 haps to the extent of one to two inches) should he made nf copper, with a 

 vol. v. no. ir. octohkr 182G. / 



