Polytechnic Association. 613 



t 

 action of ages is merely concentrated by artificial means — and the 



wonder is, why has nature remained so long without imitators — in an 

 action of elements against which constructors and engineers are for- 

 ever fighting. 



Mr. Tilghman first applied a jet of sand driven by high pressure 

 steam to cut stone, but later experiments have proved that the work 

 can be done with an air blast of lighter pressure, and excellent results 

 have been obtained from a current of air caused by a fan blower. 



The machine now exhibiting at the fair consists of a hopper or 

 elevated box, which is supplied with sand and a flexible blast-pipe, for 

 the air or steam. The sand which is supplied to the receiving hopper 

 dry, is conveyed from thence through a flexible tube terminating into 

 a smaller tube of metal, which passes through a larger chamber or 

 tube through which the supply of air or steam is admitted. This 

 part of the machine may be called the ejector, and is made of metal. 

 The sand falling through the flexible tube into the smaller metal tube 

 is carried about four inches past the entrance of the air-blast; here 

 the air-blast tube is contracted and carried several inches further down, 

 so that the sand falling through the inner tube is met by the blast of 

 air or steam, and mingling with it, is driven forward from the nozzle, 

 striking with great force against the surface to be cut. 



The flexible sand and blast tubes allow motion and direction to be 

 given to the nozzle, and thus the surface to be cut need not be limited. 

 In the machine above described, an air-blast is used with a pressure 

 of from seventy to seventy-five pounds per square inch, though this 

 extreme pressure is not necessary for ordinary use, or to illustrate the 

 perfect action of the invention. 



A machine has been made to supply a blast of sand and air from a 

 simple fan-wheel. A quart of sand can be thrown into this machine, 

 and the surface to be frosted or cut is placed on a sliding table under 

 the broad nozzle of the blast ; the whole is then closed up and the 

 fan revolved. The sand is drawn into the air current in the center of 

 the fan and forced up and around through the flat channel or nozzle 

 against the surface to be cut ; at the same time the table slowly moves 

 across the blast, keeping the material about an inch from it. A few 

 seconds of exposure will completely destroy the smooth surface of a sheet 

 of glass and give it a beautiful frosted appearance; or if a design has 

 been previously made upon the glass with paint, paper or thin gum 

 cloth, all the interstices where the surface of the glass would be 

 exposed will be cut, while the covered portion will be left untouched. 

 The sand in the machine is used over and over again as fast as it has 



