POWDERS: – The degree of coarseness or fineness of a powder is differentiated by the nominal aperture size of the mesh of the sieve through which the powder is able to pass, expressed in μm.

The following terms are used in the description of powders:

  • Coarse powder (2000/355):- A powder of which all the particles pass through a No. 2000 sieve, and not more than 40% through a No. 355 sieve.
  • Moderately coarse powder (710/250):- A powder of which all the particles pass through a No. 710 sieve, and not more than 40% through a No. 250 sieve.
  • Moderately fine powder (355/180):- A powder of which all the particles pass through a No. 355 sieve, and not more than 40% through a No. 180 sieve.
  • Fine powder (180):- A powder of which all the particles pass through a No. 180 sieve.
  • Very fine powder (125):- A powder of which all the particles pass through a No. 125 sieve.

When the fineness of a powder is described by means of a number, it is intended that all the particles of the powder should pass through the sieve distinguished by that number.

SIEVES:- The wire sieves used in sifting powdered drugs are distinguished by numbers, which indicate the nominal aperture size expressed in μm.

The sieves are made of wires of uniform circular cross-section, in accordance with the specifications given in Table.

No. Of sieve (μm) Nominal size of aperture (mm) Nominal diameter of wire (mm) Approximate screening area (%)
2000 2.00 .90 48
710 .710 .450 37
500 .500 .315 38
355 .355 .224 38
250 .250 .160 37
212 .212 .140 36
180 .180 .125 35
150 .150 .100 36
125 .125 .090 34
90 .090 .063 35
75 .075 .050 36
45 .045 .032 34

The nominal size of aperture of wire mesh sieves has been selected principally from among those recommended in the ISO standard 565-1972.

REFERENCE LINKS

The International Pharmacopoeia – Sixth Edition, 2016