This section is from the book "Dental Medicine. A Manual Of Dental Materia Medica And Therapeutics", by Ferdinand J. S. Gorgas. Also available from Amazon: Dental Medicine.
The fineness of powder is denoted either by descriptive words (as in the case of brittle and easily-pulverizable substances), or in terms expressing the number of meshes to a linear inch in the sieve. The following degrees of fineness will prove serviceable in the preparation of dentifrices, polishing powders, etc: -
A very fine powder . . .
Should pass through a sieve having 80 or more meshes to linear inch.
=No. 80 Powder.
A fine powder.......................
Should pass through a sieve having 60 meshes to the linear inch.
=No. 60 Powder.
A moderately fine powder .
Should pass through a sieve having 50 meshes to the linear inch.
=No. 50 Powder.
A moderately coarse powder,
Should pass through a seive having 40 meshes to the linear inch.
=No. 40 Powder.
A coarse powder .
Should pass through a.
sieve having 20 meshes to the linear inch.
=No. 20 Powder.