of blowing up Rods under Water, • f 27 1 



and drive in ftrongly two plugs of dry wood to fervc as wad- 

 ding. Thefe plugs muft have a longitudinal groove, that they 

 may glide along the rod and fuller the water to efcape. 



Obfrvation. 



9th, Inftead of a rod of hollow wood you may employ, 

 with advantage, either a tube of tin plate about four milli- 

 metres in diameter, terminating at the lower extremity, which 

 muft be inferted in the cartridge in a truncated cone, and an 

 orifice of two millimetres; or a leaden pipe drawn in the 

 manner of wire- drawers, having the fame dimenfions as the 

 above, and whole refinance may be fufficient, if you take 

 care to introduce into it, while you drive in the wadding, a 

 rod which may exadtly fill the interior vacuity. 



If you have at hand anv kind of compofition capable of 

 acquiring hardnefs in a little time * at the bottom of the water, 

 you may fubftitute for the rod and metallic tubes a flexible 

 tube of cloth done over with pitch or gum. In this cafe, it 

 will be neceflary to introduce the priming rod into the tube, 

 while you drive in the wadding to prevent its depreffion. The 

 cloth of the tube, the upper extremity of which is deftined 

 to rife above the hole in the rock, muft be fufficiently thick 

 and ftrong that the p refill re of the water, which I fuppofe to 

 be fome centimetres above the ground, may not flatten it, 

 even if the liquid mould introduce itlelf between the tube 

 and the compofition. ' 



III. Method of blowing up Rocks under Water at any Depth, 



10th, This method, on the firft view, has a refemblance to 

 that firft def'jribed, flnce a tube of tin plate is employed 

 in ii ; but it differs eiTentially from it in this reipeel:, that 

 'inltcad of wadding above the charge, according tq the ufual 

 method, you employ an inflexible (hank charged with a 

 weight at its upper extremity, and terminating at the lower 

 inaiegment of an iron cylinder, which performs the office of 

 a wedge, and is applied exactly upon another iimilar wedge 

 inverted and reding on the upper end of the cartridge. 



The effect of this difpofition, as may be readily conceived, 

 is to force the wedge which adheres to the cartridge to afcend 

 a little at the time of the explofion, and to fqueeze itfelf clofely 

 againft the upper wedge fo as to elofc the hole in the rock. 



11th, The defcription of this procefs may be feen in the 



: A mixture of quicklime rani plafter newly calcined would, perhaps, 

 be of rhio kin J. 



twelfth 



