750 



SAND-BLAST 



might be hoped for; but there can be no practical objection to the use of a reasonable 

 amount of heat for such a purpose, if found necessary. A beautifully white sand 

 has been used in America in the manufacture of soap. 



The sand from Alum Bay, in the Isle of Wight, is composed of 



Silica 97 



Alumina, with trace of oxide of iron and magnesia . 2 

 Moisture 1 



100 

 The French, or Fontainebleau sand, now used in glass-making very extensively, is 



Silica 98-8 



Alumina, and trace of iron 07 



Moisture ......... 0'5 



100 



SAND-BLAST. Under the head of ENGBAVINO ON GLASS, a description is given 

 of Mr. Tilghman's process of abrading the surface of glass or stone by the action of a 

 jet of sand driven at considerable velocity. The construction of the apparatus only 

 will be dealt with in this place. The machine employed to direct the sand on to the 



1754 



1755 



r S/lf/D 



object to be operated upon 

 resembles a Gifford's injec- 

 tor. The arrangement will 

 be understood by examin- 

 g Jiff. 1754. a is the sand- 

 box, and b a box contain- 

 ing compressed air, which 

 passes through the tube c, 

 with force proportional to 

 the pressure exerted on the 

 air in the box ; opposite to 

 this jet of air and sand is 

 placed the plate of glass to 

 be operated on. The grains of sand being drawn by suction into the air, or steam, 

 if the latter is employed, and then projected forward with a velocity proportioned to 

 the pressure, the sand does its work and passes off into the settling chamber e, from 

 which it is again lifted by the sand-elevator to bo returned into the box a. For 

 cutting stone, the sand is introduced into a central iron tube, about ^th-inch bore 

 (Jiff. 1755), and the steam issues through an annular passage surrounding the sand- 

 tube. A tube of chilled cast iron, 6 inches long, and ^ths-inch bore, is fixed as a 

 prolongation of the steam passage, and serves as a tube in which the steam mixes 

 with the sand, and imparts velocity to the latter. The central sand-tube is con- 

 nected by means of a flexible tube and funnel, with a box containing dry sand, 

 and the outer annular tube is connected by another flexible tube with a steam-boiler. 



