06 APPLIED SCIENCE 



98. The Use of Compressed Air in a Sand Blast. Sharp 

 sand under air pressure is used in etching or frosting glass 

 and cleaning castings. The pressure of the air and hardness 

 of the sand is governed by the class of work. 



A sand blast outfit includes a sand blast machine, hose 

 and nozzles, and a standard air compressor of the size and 

 pressure capacity required by the conditions of the work, 

 together with a good-sized air receiver with the usual gauges, 

 safety valves, and drain cocks. If air is. already in use at 

 the location, at higher pressures than required for the sand 

 blast operation, a pressure reducing valve may be installed, 

 leading preferably to a separate receiver which will be main- 

 tained at the proper pressure for the sand blast operation. 



A clean, sharp sand, thoroughly dried, will give best results, 

 and it is essential that the air used with the blast be kept as 

 dry as possible by the installation of blow-off cocks, and 

 occasionally "U" loops introduced in the line of air piping, 

 with drip cocks installed at the bottom of the loops; or by 

 the ordinary bucket steam trap. Sand especially suited to 

 the operation can be obtained from manufacturers of the 

 sand blast machines. 



For etching on, or frosting glass, a pressure of 2 to 5 Ibs. 

 is ample; for cleaning brass castings and removing core 

 sand, 15 to 20 Ibs. ; for cleaning the general run of iron cast- 

 ings, 15 to 20 Ibs.; and for steel castings, 30 to 75 Ibs. 



99. Siphon. In commercial and industrial plants it is 

 often necessary to remove a liquid in a small stream from a 

 large cask, without disturbing a sediment, to fill smaller 

 receptacles. This is particularly true in the case of corrosive 

 liquids, like acids, ammonia, etc., where there is great danger 

 in pouring the liquid from the cask. In such cases the task 



