796 TEA^'SACTioys of the American Ixstitute. 



that was now needed was tke electric spark to pass through the wires 

 to explode all the cans simultaneously. 



AYe then passed down the tunnel, leaving the infernal apparatus in 

 darkness, to the ends of the prime Avires a few feet behind the 

 machines and shields just referred to. Here Mr. Brown connected 

 the two wires to a small static electrical machine, made of vulcanite, 

 and containing within one of its chambers a condenser. After about 

 six turns of the crank of the machine, the accumulated electricity 

 was discharged, and the seventeen pounds of nitro-glycerine exploded 

 at once. At this moment the workmen had receded to beyond the 

 shaft, and Mr. Brown had sent an assistant still farther off with the 

 remaining three pounds of nitro-glycerine in the basket. 



The shock of the explosion was felt instantaneously with the 

 discharge of the electric current. The deep report was more like 

 what I would imagine would be the effect of the loudest " thunder 

 clap " confined in a like subterranean alley, than any effect I can 

 think of to compare it with. 



I was told that the force of air issuing from the top of the shaft is 

 sufficient, on these occasions, to lift the hats of those near it, and that 

 the vibrations are distinctly felt at the surface, through the nearly 

 600 feet of rock and earth above the blast. 



The use of nitro-glycerine is hastening the work forward. One of 

 the foremen of the shaft informed me that with this, one hole 

 accomplished the removal of as much rock as three holes charged 

 with powder, and in " stopping out bench work," one hole with nitro- 

 glycerine is equal to eight charged with powder, in execution of work. 



The nitro-glycerine is made at the laboratory constructed for the 

 purpose near the shaft, under the direction of Mr. George M. 

 Mowbray, who has recently made some valuable improvements in its 

 manufacture. 



They frequently make here 150 pounds daily. 



On entering the converting department of these works the first 

 that attracts' the attention is a long trough, resembling a manger for 

 feeding horses, about three feet above the floor, and fifty feet in whole 

 extension, filled with ice and a little salt. 



In this, about two feet apart, are earthen jars holding a gallon 

 each, their tops projecting two or three inches above the ice. In 

 these jars is the nitric and sulphuric acids. Immediately over the 

 jars, two feet above, resting in a wuod rack, are inverted cans, 

 holding about one quart of glycerine. This drops into the acid 



