200 Miscellanies. 



touch hole is stopped air tight by the powder, the gun with the ram- 

 rod is then converted into a complete ^/irepMmp. The vent of ar- 

 tillery should never be closed whilst the charge is ramming down, as is 

 sometimes done by the finger of an assistant, and the pans of mus- 

 kets and pistols should always be left open ; yet, after all, if the 

 chamber of a gun is rendered air tight by the stoppage of the vent 

 by the powder, it is easy to conceive that by the ramrod and wadding 

 the gun may at once be converted into a fire pump, and that, by a 

 violent thrust of the ramrod, fire may be generated between the wad 

 and powder. The only safe course is, therefore, not to use very 

 great force in driving down a charge ; and to keep the head and 

 body averted from the mouth of the piece. 



But in relation to blasting rocks, the most proper substance for 

 confining powder, is a plug of green wood with either a hole through 

 it, or a small semicircular excavation in one side of its whole length 

 which may be filled with powder, and fired after the plug is driven 

 in. It is apparent that the hole or excavation in the plug will prevent 

 the compression of the air ; and that, while dry wood might be sus- 

 pected of exciting the electric spark by friction against the sides of 

 tlie hole in the rock whilst driving it forcibly down, that green wood 

 will not have that effect. Since the above accident I have, in a few 

 instances, seen this method tried successfully by my own advice. 



March 24, 1830. — ^The principle of the Jire pump, (so far as 1 

 am informed,) not having been considered in its application to forc- 

 ing down the wadding or covering of powder in a rock, I am in- 

 duced to call your attention to the fact that it is often done, with 

 great force and violence j as was the case in the instance at Bozrah 

 Ville. The two workmen, vi^ho were there blown up, were alternate- 

 ly employed in striking down the covering, which was of pounded 

 brick, on to the powder with a sledge weighing fifteen pounds ! 



The method adopted by your correspondent* of covering the 

 charge of powder with a wooden cone, and filling the interstice with 

 sand, steers clear of the principle of the Jii'e pump, and is perhaps 

 the best method yet discovered. 



*See the paper of Mr. Blake, Vol. 17, p. 1S4. 



