WASHING or the separation of powders into different degrees of fineness by washing over or elutriation. - On the advantages of the careful separation of the polishing powders some remarks were offered in the introduction to this division of the work (see page 1031); the practice of washing, which is within the reach of every one, is described in this Catalogue under the head Emery, articles 3, 4, 5 and 6.

The author has been in the habit of washing some others of the polishing powders, but generally into two sizes only of each; the times employed for their respective depositions, which are somewhat influenced by the specific gravities of the substances are subjoined.

Powder.

No. 1.

No. 2.

Chalk.............

1 minute

2 minutes

Crocus................

10 seconds

30 seconds

Oilstone Powder........

30

,,

3 minutes

Pumice-stone Powder.........

30

,,

3

,,

Rottenstone..............

30

,,

3

,,

Tripoli..............

30

,,

1

,,

Washing is constantly employed in metallurgy, for the separation of the metallic particles from the earthy matters in the pounded ores; in the manufacture of porcelain for the separation of the coarse and large particles from the fine clay, and prepared flint, therein used, and in the preparation of polishing powders and some drugs. ATCHWORK. - As regards the parts in steel, see Machinery, article 13, and the parts in brass see Brass, article 6.