among mechanics, a tool used in order to smooth, polish, or cut metals. This instrument is of iron or forged steel, cut transversely in little furrows, with chisel and a mallet, and of a depth corresponding to the grain or touch required. After cutting the file, it must be tempered with a composition of chimney-soot, very hard and dry, diluted and wrought up with urine, vinegar, and salt, and the whole reduced to the consistence of mustard. Tempering files consists in rubbing them over with this composition, and in covering them with loam; after which they are put in a charcoal fire, and taken out by the time they have acquired a cherry colour, which is known by a small rod of the same kind of steel put in along with them. Being taken out of the fire, they are thrown into cold spring water, and subsequently cleaned with charcoal and a rag; after which they are kept dry and free from rust by laying them up in wheat bran. Iron filings require more heating than steel ones. Files are of different forms, sizes, cuts, and degrees of fineness, according to the different uses and occasions for which they are made.