SAND, which is nearly pure silex, is used in sawing and smoothing building stones and marbles, and in many other of the preliminary grinding and polishing processes. River sand and pit sand are in general sharper than sea sand, which is more rounded by attrition. Stone masons prefer the scrapings of roads that have been repaired with flint stones, the particles of which become knocked off and abraded by the traffic; and engineers sometimes employ grindstone dust, collected after turning the grindstone into form, or obtained by crushing the grit or sandstone with a hammer; or pestle and mortar, as the grindstone dust cuts more sharply than Flanders brick, another form in which sand is employed.

2. - Trent Sand is collected from the banks of the river of that name which runs into the Humber. It is largely employed at Sheffield, and somewhat throughout England generally, for polishing. This sand is remarkably fine and sharp, and serves very economically many of the purposes of emery and other polishing powders prepared by art, it is very much used for Britannia metal goods.

The Sheffield cutlers are in the habit of making the Trent sand with water, into balls two or three inches diameter. The balls when dry are burned for a few hours in the kitchen fire, and from being of a moderately dark brown, become brick red. The lumps are then crushed between the hands and passed through a fine hair sieve. The burnt sand is considered to cut quicker than the unburnt.

For common work they use the blue stone pulverized and sifted instead of Trent sand, that is, the blue grit stone, not the blue hone slate used for brass work, etc. Flanders brick when scraped may be used as a substitute for Trent sand, but being contaminated with the clay required in forming the brick, it cuts less keenly than the unmixed sand.

3. - Sand Paper is made with the common house sand, and only of one degree of coarseness, but in other respects exactly like glass paper, to which it is greatly inferior; as the particles of sand are less angular and cutting than those of glass, when applied upon wood, etc, but on metals sand paper assumes a character intermediate between glass paper and emery paper.