On Blasting Rocks, and Tamping* Oi) 



or where, from the density of the rock, or its being confined 

 as in the shafts and levels of mines by the numerous points 

 of contact, very great force is required to produce its frac^ 

 ture. 



i ani inclined to believe that though in thefet ca^eS both 

 sand and clay niiist yield to the usual mode of tamping, 

 yet that clay will commonly produce the fracture where 

 fand will fail to do so. About t4en years ago an experi- 

 ment was made in Cornwall upon a loose rock on the sur- 

 face, and sand was blown out without any effect having 

 been produced: an equal quantity of gunpowder, confined 

 by a small quantity of tamping, broke the rock ; which 

 proved that the resistance was far inferior to that of the com- 

 mon mode. And from many late trials made with clay, in 

 holes tnoderately deep, in Wheal Friendship copper min6' 

 and the tunnel of the Tavistock canal, I have found clay to 

 answer nearly a« well as tamping; though certainly in what 

 the workmen call shallow holes, and in vfery hard rock, 

 neither that nor sand can be depended upon. In quarries 

 and open works where deep holes can and always ought to 

 be had, where the groutid is for the most part dry, and the 

 rock is seldom very hard, both will be found eminently 

 iiscfiil, and will contribute much to the safety of the work- 

 men. ' 



Mr. Farey m;;ntions, in his letter in your Macrazine, his 

 having seen coal -ashes employed as tanipipg. The fact is, 

 that mo»t friable substances are proper for this purpose, 

 those being the best" that combine with friability a cer- 

 tain degree of tenacity : the miners esteem soft yellow copper 

 Ore, or the common galena, in the highest degree, and next 

 perhaps is broken tile; but what is commonly used is the soft 

 6chis)tus rock which is attendant on most metallic veins. 



These substance^ are beaten into the hole upon the charge 

 of gunpowder, while a small taper iron rod called the nail, 

 kept in during the process, forms, on being withdrawn, the 

 vent for the rush tilled with gunpowder, which constitutes 

 the fuse. It is by the occasional attrition of this iron nail 

 against siliceous particles, either in the act of ramming^ 

 striking it out, that dreadful accidents sometimes occur. 



G2 The 



