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`
`BRITISH
`PHARMACEUTICAL
`CODEX
`1973
`
`Prepared in the Department of Pharmaceutical Sciences
`of the Pharmaceutical Society of Great Britain
`and published by direction of the Society's Council
`
`LONDON
`THE PHARMACEUTICAL PRESS
`17 BLOOMSBURY SQUARE WCIA 2NN
`
`

`

`Copyright © I973
`by the Pharmaceutical Society of Great Britain
`
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`Made and printed in Great Britain by
`William Clowes & Sons, Limited, London, Beccles and Colchester
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`antimony trichloride solution, at the maximum
`at about 500 nm, using ethylene chloride as the
`blank.
`The amount of calciferol, in mg, in the weight of
`sample taken is given by the formula:
`
`0·04(e1 - e2)
`(e3 -
`e1)
`
`DETERMINATION OF VITAMINS
`911
`where e1 = the extinction due to the solution in
`the first tube,
`e2 = the extinction due to the solution in the
`second tube, and
`e3 = the extinction due to the solution in the
`third tube.
`Each mg of calciferol is equivalent to 40,000 Units
`of vitamin D.
`
`Appendix 25
`
`Powders and Suspensions
`
`A. Classification of Powders
`The descriptive term used to indicate the degree
`of comminution of substances employed in the
`manufacture of preparations in the British Pharma(cid:173)
`ceutical Codex can usually be related to the size
`of the mesh of the sieve or sieves through which
`the whole or a portion of the powder is able to
`pass. The wire sieves used in sifting powders are
`distinguished by numbers and should comply with
`the requirements of British Standard 410: 1969.
`In the British Pharmacopoeia and the British
`Pharmaceutical Codex, sieves were formerly
`designated by the mesh count or mesh number
`which was the number of meshes per inch. Sieves
`are now designated by aperture size and the
`numbers
`indicate the nominal aperture size,
`measured in millimetres for aperture sizes of
`1 mm or greater and in micrometers (µm) for
`aperture sizes of less than 1 mm.
`The table below relates the sieve numbers now
`used to the mesh numbers formerly used. The
`relationship of the mesh number to the actual
`number of meshes per inch depends on the wire
`diameter and should be taken as an approximation.
`
`Sieve
`Number
`
`Mesh
`Sieve
`Mesh
`Number Number Number
`
`mm
`4·00
`3·35
`2·80
`1-70
`µm
`710
`500
`
`4
`5
`6
`10
`
`22
`30
`
`µm
`355
`250
`180
`150
`125
`106
`75
`
`44
`60
`85
`100
`120
`150
`200
`
`The following terms are used in the description
`of powders:
`COARSE POWDER. A powder of which all the par(cid:173)
`ticles pass through a No. 1·70 sieve and not more
`40·0 per cent pass through a No. 355 sieve.
`MODERATELY COARSE POWDER. A powder of which
`all the particles pass through a No. 710 sieve and
`not more than 40·0 per cent pass through a
`No. 250 sieve.
`MODERATELY FINE PoWDE~. A powder of which
`all the particles pass through a No. 355 sieve and
`not more than 40·0 per cent pass through a
`No. 180 sieve.
`
`FINE POWDER. A powder of which all the particles
`pass through a No. 180 sieve.
`VERY FINE POWDER. A powder of which all the
`particles pass through a No. 125 sieve.
`ULTRA-FINE POWDER. A powder of which the
`maximum diameter of 90 per cent of the particles
`is not greater than 5 µm and of which the
`diameter of none of the particles is greater than
`50 µm.
`When the degree of comminution of a powder is
`defined by means of a number, the whole of the
`powder passes through the sieve described by that
`number.
`
`B. Determination of the Surface Area of
`Bephenium Hydroxynaphthoate
`Determine by the air-permeability method de(cid:173)
`scribed by F. M. Lea and R. W. Nurse, J. Soc.
`Chem. Ind., Lond. (Transactions), 1939, 58, 277-
`283, using a compact 2·54 cm in diameter, 1 ·00 cm
`in height, and having a porosity within the range
`0·475 to 0·525.
`For the purpose of the calculations, the density
`of the particles may be assumed to be 1 ·298 g
`per cm3•
`
`C. Determination of Particle Size in
`Suspensions
`The following method is
`to be used, when
`directed, to determine the particle size of a sus(cid:173)
`pended solid in a preparation:
`Dilute a suitable quantity of the preparation with
`an equal volume of glycerol and further dilute, if
`necessary, with a mixture of equal volumes of
`glycerol and water; alternatively, where specified
`in the individual monograph, use liquid paraffin as
`the diluent.
`Mount the diluted preparation on a slide and
`examine random fields microscopically using a
`microscope providing adequate resolution for the
`observation of small particles.
`Observe that there are no particles (or, if stated,
`not more than a few particles) above the maxi(cid:173)
`mum size permitted in the individual mono(cid:173)
`graph.
`Count the numbers of particles having maximum
`diameters above and/or below the limiting sizes
`permitted in the individual monographs and
`hence calculate the percentages of particles having
`maximum diameters within the stated limits.
`The percentages should be calculated from
`observations on at least 1000 particles.
`
`