248 W. 0. DUNTLEY 



power to them through insulated wires. This, too, called 

 for a rubber hose, though of such small diameter that it re- 

 ceived the name of insulator instead, and still the proper 

 flexibility in the power plant was wanting. The work must 

 still be brought to the tool. Thus far the shop or mill owner 

 had profited only in the saving in cost of his transmission. 



All the small work such as boring, drilling, chipping, 

 cutting, calking, riveting, upsetting and 101 other operations 

 were still dependent upon the muscular arm of the mechanic 

 whose slow and measured stroke consumed valuable time. 

 True flexibility is only reached when the tool may be brought 

 to the work as the hammer, chisel, brace, screw driver, plane, 

 etc. Just here the third entry in the great race for suprem- 

 acy made its appearance. Coming upon the scene scarce 

 a decade ago, with rapid bounds it reached the home stretch 

 and is now running under the wire several lengths ahead. 



This competitor for utility and popularity is air — com- 

 pressed air — and it enters into the struggle well adapted in 

 every particular for the sharp contest. If its expansibility 

 be not so great as steam, it is for that reason a much safer 

 agent to confine, and its compression may be run up far be- 

 yond the safety line of steam. An explosion of a vessel 

 containing compressed air, even up in the hundreds of pounds 

 to the square inch, is rarely attended with serious conse- 

 quences to bystanders or operatives. Unless carried to 

 excessive pressures it is not inconveniently warm to handle, 

 a circumstance which militates greatly against the use of 

 steam; moreover, it even becomes cooler while doing its work, 

 and is for this reason used for ventilation in mines and closed 

 caissons. For the uninitiated it is absolutely impossible 

 to conceive of the revolution in all lines of trade and manu- 

 facture that these pneumatic tools have caused. At first 

 the use was confined to larger operations and we had such 

 tools as pneumatic rock drills, both rotary and percussive, 

 channellers, gadders, etc., for ordinary excavating and quarry 

 work, for which rough work large and unwieldy tools were 

 made. Later these tools were made in smaller sizes adapted 

 to the use of one man for coal mines and the mining of min- 

 eral ores, and these tools have continually decreased in size 



