( Reaffirmed 2000 )
IS : 5258  1969
Indian Standard
DETERMINATION OF PARTICLE SIZE OF POWDERS BY OPTICAL MICROSCOPE METHOD
Sieves, Sieving and Other Sizing Methods Sectional Committee, BDC 19
Chuirman
DR K. N. MATHUR C/o National Physical Laboratory, Hillside Road, New Delhi 12
Members
SHRI A. P. AQARWAL
Representing
Defence Production Organization ( Ministry of Defence ) Shalimar Wires & Industries Ltd, Uttarpara S&RI S. N. ARORA SRRI D. N. CRAKRABORTY (Alternate) Krishanlal Thirani & Co Ltd, Calcutta SHRI S. K. BAJORIA SHRI S. K. GANDHI ( Alternate ) All India Instrument Manufacturers and Dealers SHRI N. N. BANERJEE Association ( Bombay Region ) National Instruments Ltd, Calcutta SHRI R. R. CHAERABORTY All India Instrument Manufacturers and Dealers SHRI K. C. CHANDIOE Association ( Delhi Region ) SHRI P. N. SOOD ( Alternate ) Central Water & Power Commission, New Delhi DR I. C. DOS M. PAIS CUDDOU SHRI S. V. SURYANARAINA ( Alternate ) The Indian Steel & Wire Products Ltd, Jamshedpur SHRI HARCHAND'SINOH SHRI R. R. KAPLISH (Alternate ) The Associated Cement Companies Ltd, Bombay DR R. R. HATTIANQADI DR M. K. GHARPUREY ( Alternate ) Directorate General of Factory Advice Service and SHRI H. N. JA~TIANI Labour Institutes. Bombav ' JOINT DIRECTOR, RESEARCH Ministry of Railways ' I F. E. ). RDSO DIRECTOR, REDEPUTY SEARCH ( F. E. ), RDSO ( Alternate ) Research & Development Organization ( Ministry of LTCOL T. C. JOSEPH Defence ) SHRI N. MOHAN RAO ( Alternate ) Hindustan Boilers, Bombay SHRI D. S. JOSKI SHEI CHANDRARANT L. KHAQRAY All India Wire Netting Manufacturers' Association, Bombay ( Continuedan page 2 )
INDIAN
MANAK
STANDARDS
BHAVAN, 9 BAHADUR NEW DELHI
INSTITUTION
SHAH 1 ZAFAR MARG
IS : 5258 1969
( Continued from page 1 ) Members Representing
SHRI V. KRISHNAMOORTFIY Directorate General of Technical Development Directorate General of Technical Development SHRI R. N. MALLICK SHRI H. M. MARWAH Hindustan Wire Netting Co Ltd, Bombay SHRI G. H. MARWAH ( Alternate ) SARI PREM PRAKASH National Physical Laboratory ( CSIR ), New Delhi
SHRI R. RAJARAMAN SHRI E. K. RAMCHANDRAN DR B. RAO SHRI D. D. BHUPTANI ( Alternafe ) SHRI K. K. SEN~UPTA SHRI A. K. SEN (Alternate ) SHRI P. V. SUBOA RAO SHRI K. C. TOSIINIWAL
Central Board of Irrigation & Power, New Delhi National Test House. Calcutta The Tata Iron & Steel Co Ltd, Jamshedpur
Hindustan Steel Ltd, P. 0. Dhansar
The Andhra Scientific Co Ltd, Masulipatam All India Instrument Manufacturers & Dealers Association ( Calcutta Region ) Associated Instrument Manufacturers ( India ) Private SHRI H. C. VERMA Ltd, New Delhi SHRI A. V. A. SHASTRI ( Alternate) Director General, IS1 ( Exoj'icio Member ) SHRI R. NAQARAJAN, Director ( Civ Engg ) Secretary SHRI VINOD KUMAR Assistant Director
Sizing
( Civ Engg ), ISI
BDC 19 : 2
Poona
by Methods
Other
Than
Sieving Subcommittee,
Meteorology,
Convener DR BH. V. RAMANA MURTY Members Associated Instrument Manufacturers ( India ) Private Ltd, New Delhi SHRI A. V. A. SHASTRI ( Alternate ) The Fertilizer Corporation of India Ltd. New Delhi SHRI K. C. BANERJEE l&S. K. GHOSU ( Alternate ) The Associated Cement Companies Ltd, Bombay Dlt M. K. GH~RPUREY National Physical Laboratory ( CSIR ), New Delhi DR P. T. JOHN The Standard Batteries Ltd, Bombay Soar B. S. KEDARE SHRI R. S. MANI ( Alternate) Philips Carbon Black Ltd, Durgapur SRRI A. ROY Central Scientific Instruments Organization ( CSSR), SHRI K. D. SHlRMA Chandigarh
SHRI M. N. BALIQA
Institute of Tropical
2
IS:525St989
Indian Standard
DETERMINATION OF PARTICLE SIZE OF POWDERS BY OPTICAL MICROSCOPE METHOD
0. 0.1 This FOREWORD
Indian Standard was adopted by the Indian Standards Institution on 13 August 1969, after the draft finalized by the Sieves, Sieving and Other Sizing Methods Sectional Committee had been approved by the Civil Engineering Division Council. 0.2
optical
Of the various methods employed for particle size determination, the microscope method is the only one in which direct observation Even this method has one drawback is made of the size of the particles. in that it has a tendency to measure the largest dimensions unless the particles are properly dispersed with random orientation. Also, the method is too much time consuming for extensive use between purchaser and supplier for determining conformity to specifications. But it may be used advantageously for two purposes, namely, (a) as a basis of calibration for faster methods such as those involving sedimentation and !b) in the determination of the particle size of routine samples, specially in the cases where particles are of such shape that they do not obey Stokes's law. 0.3 A number of methods are available for the determination of particle These are the microscope, elutriation, size in the range 1 1 000 microns. sedimentation, and sieving. As no single method is applicable to the whole range of size 1  1000 microns, it is necessary to combine the analysis of two or more different methods in order to establish the distribution in full. Moreover, the results obtained on particles between a given size range are not the same when determined by any two methods mentioned above. It is found that particle size determined by one method may be corelated to the size determined by another method by a certain multiplying factor. The correlation factors to be used in correlating particle size determined by various methods are given in Appendix A. 0.4 In the formulation of this standard due weightage has been given to international coordination among the standards and practices prevailing in different countries in addition to relating it to the practices in the field in this country. This has been met by deriving assistance from the following publications: B. S. 3406: Part 4: 1963 (Methods for determination of particle size of powders, Part 4 Optical microscope method' issued by the British Standards Institution. 3
IS : 5258  1969 ASTM Designation: E 2062 T Tentative recommended practice for analysis by microscopical methods for particle size distribution of particulate substances of subsieve sizes. 0.5 In reporting the result of a test or analysis made in accordance with this standard, if the final value, observed or calculated, is to be rounded off, it shall be done in accordance with IS: 21960*.
1. SCOPE 1.1 This standard describes the optical microscope method for determining the particle size of powders which pass through a 75micron IS Sieve IS :46019627 as far as the particle shape and refractive index will permit. The method of measurement is SO arranged that the size analyses of the particles, in microns, are expressed in the form of a consecutive 42 series, namely 75,53,37,27, 19, 13,9*4,6*6,47,3.3,2*3, 1.7, 1.2, O8, O6$. 1.2 The size distribution is expressed either by number or by volume or weight and in terms of the diameters of circles having the same projected The method is normally used for particles having areas as the particles. projected diameters in the range O6 75 microns but the upper size limit can be extended to measure particles up to 150 microns ( see 4.3). 2. TERMINOLOGY 2.0 For the purpose of this standard, the following terms and definitions that given in IS : 41241967s shall apply. and is is
2.1 Laboratory SampleThe portion of the gross sample which delivered to the laboratory for determination of particle size distribution. 2.2 Analysis Sampleused in the size analysis The portion apparatus. of the laboratory sample which
2.3 Intermediate SampleThe includes the analysis sample. 3. OUTLINE OF METHOD
portion of the laboratory
sample which
3.1 A representative sample of the powder to be sized is dispersed and The particles are viewed through a microscope by placed on a glass slide. means of transmitted light. The areas of the magnified images of the
*Rules for rounding off numerical values ( rev&cd ). tspecification for test sieves ( revised ). $The IS0 series is 63, 4% 31, 2% 16, 11, 7.8, 5.5, 3.9, 2.8, 2.0, 1.4, 1.0. The optical microscope method as given here does not apply to this series. A different graticule would be needed. @lossary of terms relating to powders.
IS : 5258 1969
particles are compared with those of the reference circles of known size inscribed on a graticule and simultaneously visible. The relative numbers These of particles in each of a series of size classes are determined. constitute the size distribution by numbers, expressed as percentages, number. From the relative number in the size classes the relative volumes are calculated, assuming that particles of all sizes have the same shape. The relative volumes, expressed as percentages, constitute the size distribution by volume. The same is the size distribution by weight also if particles of all sizes have the same density. 3.2 Particle ShapeThe great majority of particles may depart from the regular form to a greater or lesser extent the extremes being needles and plates. The measure of deviation which is called the shape factor is unimportant for particles of size below 75 microns except in the case of Such particles may materials which are predominantly acicular in form. be assessed according to their lengths and breadths in the manner (nonstandard) as indicated in Appendix B. 3.3 The accuracy of size measurement is dependent upon the following:
4 b)
The optical quality of the images, which calls for the use of an adequate numerical aperture of the microscope objective and condenser for the size of the particle being measured; The accurate measurement of the magnification factor at the plane of the graticule on which the reference circles are inscribed; reliability of comparison reference circles; The uniformity The number of dispersion of particles of the image areas with those of the
Cl The 4
e)
on the slide; and
counted.
4. SUBDIVISION
OF SAMPLE
4.1 Methods of preparing the laboratory sample SO as to be representative of the gross sample are given in IS : 48791968*. 4.2 Method of Preparing the Analysis Sampleanalysis is prepared as detailed in Appendix C. The sample for
4.3 Upper Limit of Size Measurement This is determined by the increasing difficulty of measurement of the larger and larger particles, due to their thickness in relation to the depth of focus of the optical system, and by the availability of a suitable method of sieve analysis for such sizes. The optical microscope method is, therefore, preferably restricted to sizes Particles of size up to 150 of particles passing a 75micron IS Sieve. microns may be counted and sized, provided that the weight of particles
*Methods size. of Subdivision of gross sample of powder used for determination of particle
5
I9 : 5259  1969 of sizes retained on a 75micron IS Sieve does not amount to more than 10 percent of the total weight of the powder. In case the weight exceeds 10 percent, these particles should be removed and analysed by sieving. 4.4 Lower Limit of Size Measurement This is determined by the resolving power of the microscope. The method described here is applicable to particles of size 0.6 ( more correctly 0.59) microns and above. Any smaller particles present in the sample should not be sized, but their presence should be stated in reporting the results. 4.5 Size Classes Table 1 gives the recommended values of the size class limits which have been calculated from a base value of 53 microns. 5. APPARATUS 51 MicroscopeThe equipment shall be adequate for the work, the strictest specifications being imposed by the size of the smallest particles to be classified. The microscope used should be stable and be protected from vibration. All units of the microscope should be permanently attached to a common base. The numerical aperture should be adequate for the magnification involved. 5.1.1 The microscope (Fig. 1 ) should be provided with: (a) a source of illumination, (b) coarse and fine focusing, (c) focusing and centring substage condenser, (d) adjustable substage condenser diaphragm, (e) a mechanical stage with graduated movements at right angles, each capable of being read to 0.1 mm, (f) objectives to cover the whole ranges of sizes from 0.6 to 150 microns, (g) an eyepiece which should preferably be of focusing type, (h) a graticule and (j) a stage micrometer. The microscope to be used shall be of any of three following types:
a) b) cl
Bench microscope with a graticule mounted in the eyepiece. The microscope should be fitted with a graduated draw tube ad.justable over a range preferably from 140 to 200 mm. Projection microscope with graticule mounted in the eyepiece. The microscope should be fitted with a graduated adjustable draw tube as for the bench microscope. Projection microscope posed on a projection graduated adjustable distance. with a graticule incorporated in or superimscreen. The microscope may have either a draw tube or an adjustable projection
5.2 Microscope Lamp and FiltersThe source of illumination used shall be a relatively homngenous light source and shall be capable of filling uniformly the whole field of view of the lowest power objective. It shall be provided with an adjustable diaphragm. Coloured and neutral filters are required for controlling colour and intensity of the illumination. The use of monochromatic illumination is recommended when sizing particles smaller than 2.3 microns.
IS : 5256 1969
TABLE 1 RECOMMENDED VALUES FOR ( Clauses 4.5, 5.6.2 and 7.3 ) TO SIZE CLASSES*
SIZECLASS NUMBER
UPPER AND LOWERLIMITS SIZECLASSIN MICRONS
' Expressed to Two Decimal Places
Rounded Figures
'
ARITHMETIC MEANOFSIZE CLASS LIMITS INMICRONS (EXPRESSED TOTHREE SIQNIFICANT FIGURES) d
WEIQHTINQ FAOTOR BORCLASS (TOBEUSEDIN DERIVATION OB WEIGHT DISTRIBlJTION)t
(4'
(5) 0.36 1.00 2.83 ' 880 22.7 64.0 181 512 1450 4 100 11600 32 800 92 700 262 000 741000 2 100 000
(1)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
(2) 0.59 0.83 :::7" 1.17 1.66 l66 234 2.34 3.31 3.31 468 4.68 6.63 6.63 9.37 9.37 13.25 13.25 18.74 18.74 26.50 26.50 37.48 37.48 53.00 53.00 74.95 74.95 10600 106.00 149.90
(3) 0.6 0.8 ) 0.8 l2 > 1.2 l7 > ;:; ;I; 3.3 4.7 4.7 6.6 66 9.4 9.4 13.0 13 19 :"7 z: ;; 53 75 1;: 106 150 ) >` > > > ) > ) > ) > ) >
(4) 0.71 1.oo I.41 2.00 2.83 4.00 5.66 8.00 11.3 16.0 226 32.0 45.2 64.0 90.5 128
*Recommended values constitute a d/series based on 53.00 microns ( w 4.4). *The values for weighting factor ds are computed from the means of the class limits ( second column ), not from the rounded means given in the fourth column. "
7
IS : 5258  1969  The objectives shall be of good quality, in sound condition and inscribed with their focal length and numerical aperture. Objectives may be achromatic, fluorite or apochromatic. It may be necessary to have available at least 3 objectives to cover the whole range of sizes from 0.6 to 150 microns. 5.3 Objectives
It shall be of good quality, 5.4 Eyepiece  Only one eyepiece is required. Eyepieces may in sound condition and inscribed with its magnification. be of Huygenian ( negative) or compensating (negative or positive) type. Compensating eyepieces should be employed with apochromatic fluorite Eyepieces in which graticuand the higher power achromatic objectives. The lens les are mounted should preferably be of positive construction. should be adjustable within its mount to permit the focusing of the graticule when resting on the field stop. The eyepiece of a bench microscope should preferably be of power x 20 but not greater than x 25. 5.5 Substage Condenser The substage condenser shall be of good quality, in sound condition and shall have numerical aperture at least as large as the numerical aperture of the objective in use. It may be necessary to have As it may not be possible to available more than one substage condenser. illuminate the whole field of view of low power objectives by means of condenser having a numerical aperture adequate for high power objectives, a threelens aplanatic condenser of 1.3 numerical aperture corrected for spherical and chromatic aberrations, whose numerical aperture may be reduced by removing the top lens, is suitable for all objectives. 5.6 Graticule  The graticule ( Fig. 2 ) shall be ruled with rectangles and reference circles to the pattern and relative dimensions specified in IS:52571969". 5.6.1 The eyepiece graticule shall be of such diameter as to fit without excessive play' into the eyepiece used. A screen graticule shall be of such size as to be contained within the field of view at the projection distance employed; the field of view will usually have a diameter of about 150 mm at a projection distance of 250 mm measured from the eyepiece and will be proportionally larger for longer distances. 5.6.2 The diameters of the reference circles should preferably be such that, within the available range of adjustment of magnification which is achieved by tube length movement for eyepiece graticules or projection distance for screen graticules, the diameters shall correspond at the field with the dimensions stated in co1 2 of Table 1 (see 1.1). 5.7 Stage MicrometerThe stage micrometer shall have 100 divisions each of 10 microns. 5.8 Procedure for Adjustment of Microscope The recommended procedure for adjustment of microscope is given in Appendix D.
*Specification for eyepiece and screen graticules for the determination size of powders. of the particle
18:32581969
`0
2. y) "0
"0
"0
7(J
J.
J.
Y
Y
.
FIG. 2 6. SELECTION
INDIAN STANDARD GRATICULE AND EYEPIECES
OF OBJECTIVES
6.1 Minimum Numerical Aperture An objective shall not be employed for sizing of particles below the minimum particle size considered appropriate to its nominal numerical aperture as given in Table 2. The minimum particle size in microns is equal to 1.5 divided by the nominal numerical aperture (except in the case of an apochromatic objective of numerical This condition ensures that the diameter of the aperture 1.3 and above). smallest particle examined will be some five times that of the airy disc. It is recommended that wherever possible sizing should not be extended below the size class given in co1 6 of Table 2. 6.1.1 The manufacturer's rated value for the numerical aperture as inscribed in the ob&jective may be taken for the numerical aperture, When the rated value exceeds unity the particles should be mounted in a medium of refractive index greater than 1.3 and both condenser and objective should be oiled to the slide by immersion oil. If, on the other hand, the particles are dry mounted, or the condenser or objective is not oiled to the slirle, the nominal numerical aperture shall he taken as 1O or as the rated value whichever is smaller. The fact that the condenser will be stopped down in use so that the actual or working numerical aperture is less than its nominal value does not reduce the minimum particle size which may be measured with the objective. 10
TABLE
2
MINIMUM PARTICLE SIZE FOR DIFFERENT OBJECTIVES MINIMUM TOTAL MAGNIFICATION REQUIRED ( Clause 6.1 ) NOMINAL MAGNIFICATION OF OBJECTIVE NOMINAL NUMERICAL APERTURE, NOT LESS THAN RECOMMENDED SMALLEST SIZE CLASS MICRONS
AND
FOCAL LENQTHOF OBJECTIVE
TYPE OF OBJECTIVX*
MINIMUM PERMISSIBLE PARTICLE SIZE MICRONS
mm (1) Dry Objectives 32 25 16 12 8 6 4 (2) (3) (4) (5) (6)
MINIMUM TOTAL MAGNIXICATION REQUIRED BOR SIZING DOWN TO (__7 Minimum RecommendParticle ed Smallest Size Size Class (7) (8)
Achromatic Achromatic Achromatic Apochromatic Achromatic Achromatic Apochromatic Achromatic Achromatic Apochromatic Fluorite
x x x x x x x x x x x
5 3.5 6.5 10 10 12.5 20 20 25 40 40
0.13 0.10 0.15 0.17 0.30 0.34 0.50 0.65 0.50 0.65 0.85 0.95 1.25 1.30
12 15 10 8.8 ;:t 3o 2.3 3.0 2.3 1.8 1.6 1.2* 0.6*
1927 1927 13  19 9.4 13 6.6  9.4 47  6.6 3.3  4.7 47  6.6 3.3  4.7 2.3  3.3 2.3  3.3 1.7  2*3+ O8  1*2t
:g r: 300 340 500 650 500 650 850 950 1250 2500
:: 1:: 160 230 320 450 320 4.50 650 650 880 1800 t; g
Oil ImmersionObjectives 3.75 3.6 x 45
;:;
3
Achromatic Apochromatic
1.8 J
x80100
*Achromatic includes parachromatic; apochromatic includes fluorite and semiapochromatic. *Providing particles are mounted in a medium of refractive index greater than 1.3 and both condenser and objective are oiled. Otherwise, in both cases! the minimum particle size is increased to 1.5 microns and the recommended smallest size class to 2.3  3.3 microns, the mmimum total magnifications become 1000 and 650.
5; 8
Is:s2581969 6.2 Minimum Total Magnification of Objective and Eyepiece  The total magnification of the objective and eyepiece together shall be such, that the magnified image of the smallest particle being sized exceeds 1.5 mm. This condition ensures that the magnified image is not less than about 20 times the limit of resolution of the unaided eye. 6.3 Maximum Total Magnification of Objective The total magnification employed shall not exceed 1500 cal aperture of the objective. There is no advantage further increasing the magnification, as no further detail usually be made visible to the eye. 6.4 Choice of Objectives 6.4.1 Number Size DistributionFor sizing down to 0.6 convenient series of objectives is given in Table 3. microns a and Eyepiecetimes the numerito be gained by in the object may
TABLE 3 RECOMMENDED SERIES OF OBJECTIVES FOR PARTICLES IN THE SIZE RANGE FROM 0.6 TO 136 MICRONS
PARTICLE SIZE RANQE IN MICZONS 0.6 27 FOCAL LENGTH OF OBJECTIVE 2 mm apochromat( oil immersion )
to
4.7
4.7 to
27
8 mm achromat ( or apochromat )
25 mm ( or 32 mm) achromat
to 150
6.4.2 If it is not necessary to size below 2.3 microns the use of oil immersion may be dispensed with and a 4 mm objective can be used as of the highest power. The series then will be as given in Table 4.
TABLE 4 RECOMMENDED SERIES OF OBJECTIVES FOR PARTICLES IN THE SIZE RANGE FROM 2.3 TO 150 MICRONS
FOCAL LENGTH olr OBJECTIVE 4 mm apochromat( or achromat ) 16 mm achromat ( or apochromat ) 25 mm ( or 32 mm achromat )
PARTICLE SIZE RANQE IN MICRONS 2.3 to 13 13 to 37 37 to 150
6.4.3 Weight Size DistributionParticles smaller than 2.3 micron often do not contribute significantly to weight size distribution and in such cases the series of objectives as given in Table 4 may be used. However, if the weight of particle smaller than 2.3 microns is of importance the use 2 mm oil immersion objective becomes necessary. 12
IS : 5256  1969 7. SELECTION OF GRATICULE MAGNIFICATION AND ADJUSTMENT OF
7.1 Standard Graticule  A standard graticule ( see Fig. 2 ) ruled with a rectangular grid shall be used to define the area of the field of view within The graticule is provided with two sets of which particles are counted. numbered circles ranging from +fy to 8 {Funits in diameter, which serve as reference circles for classifying by size the particles counted. 7.1.1 The relative dimensions of the grid and the circles shall be as given in Table 5. The diameters of the reference circle increase in The physical size of geometr%al progression with a constant ratio of 43. graticule rulings is designated by the length of the rectangular grid which 100 is r times the diameter of the circle numbered 1. This length is 2 marked on the graticule in millimeters to an accuracy off 2 percent.
TABLE 5 RELATIVE DIMENSIONS OF STANDARD GRATICULE
NUMERICAL VALUE UNITS* Grid length Grid breadth Distance between marks Diameter of circle 1 3' 3 6 7 *The unit is l/lOOth of the grid length. 1.41 2.00 2.83 4.00 5.66 8.00 11.31 100 50 85.4
7.1.2 The grid is also subdivided to define smaller fields of view two each l/4 and l/8 and four each l/16 of the total area of the grid for use when required. The graticule is also provided with two calibration marks at a specified distance apart on the longer axis of the grid for adjusting the magnification of the microscope (see IS : 52571969* ). 7.2 Choice of Grid Length of Eyepiece GraticuleThe procedurefor selecting the length of grid of an eyepiece graticule is described in Appendix E. size of powders.
*Specification for eyepiece and screen graticules for the determination of the particle
13
IS : 5258  1969 7.3 Matching of Reference Circle with Size Class Limits The magnification of the microscope shall be so adjusted that the diameters of the reference circles correspond to the desired size class limits as given in circles with the Table 1. The series of possible matchings of the refaence recommeded size class limits in the range from 0.6 to 150 microns is given in Table 6. At any one matching up to 7 size classes covering a range of 8
1 4 I
150 2 19
106 2573 13
75 37
53
27
37
19
27
13 3.3
19
2.3t
13t
1.7s
800
loo
9or 10 20 40
2
Oil ImmersionObjecriws o95 40,45
a
19
13
9.4
66
4.7
3.3
2*3t
1.7$
loo
or 50
1.30 4.7 3.3 2.3 I.7 1*2t 0.62 35
164)/i 9.4
6.6
Minimum Eyepiece Powerfor Bench A4icrosco~s
Minimum eyepiece power required to magnify the various circles up to the specified minimum size of 1.5 mm when for unit relamagnification, the tive approximate magnification at eyepiece graticule is: 7x 6x 5x 10x 8x 7x 15x 12x 10x 20x 16x 14x 23x 19x
25x
*The standard eyepiece graticule is not inscribed with a reference circle of diameter corresponding to the size class limits in co1 6 which are d/`Ztimes larger than those listed under reference circle number 7, but particles may be judged as being larger than reference circle 7 whilst smaller than an imaginary circle ~~ times larger. tNot recommended although permissible for achromatic objectives ( as defined in footnote in Table 2 ). $Not recommended although permissible for achromatic objectives ( as defined in footnote in Table ssible for achromatic objectives. 2 ); not permi
As in the Original Standard, this Page is Intentionally Left Blank
IS : 5258  1969 7.5.2 Place the stage micrometer (see 5.7) on the microscope stage and align it with the longer axis of the grid on the graticule. The stage micrometer should be focussed AFTER focussing the eyepiece graticule for bench microscopes and BEFORE for projection microscopes. Adjust the magnification of the microscope by altering the tube length until there is exact correspondence between the distance separating the two calibration marks on the graticule and the length on the stage micrometer as specified in Table 7. Repeat the process whenever the objective or eyepiece is changed. The optical conditions when adjusting the magnification, including the colour of the illumination and refractive index of the immersion oil, if used, shall be the same as those obtaining when the slide of particles replaces the stage micrometer. * 7.5.3 If it is not possible to effect the adjustment within the range of tube length movement or if the reference circles are to be matched with size class limits other than those given in Table 6, the magnification at the graticule shall be measured by means of the stage micrometer and the corresponding size classes calculated. For this purpose the length of the grid, or the distance between the calibration marks, may be compared with the divisions of the stage micrometer. High power objectives should be used as far as possible near the tube length for which they have been corrected in order to obtain optimum optical performance. 8. DETERMINATION DISTRIBUTION OF NUMBER OR WEIGHT SIZE
8.1 Preparation of the analysis SampleThe sample is prepared in The concentration of particles on the the manner as indicated in 4.2. slide should be so adjusted when preparing it that each field of view contains on an average about six particles of the size class being examined. In general, a lower concentration is required when determining the number size distribution than when determining the weight sizt distribution. 8.2 AdjustmentThe microscope should be set up and adjusted in the manner as detailed in Appendix D. It is desirable to employ monochromatic illumination if particles of size smaller than 2 microns are to be The appropriate objectives, eyepiece and included in the measurements. graticule should be selected as stated under 5, 6 and 7. The magnification should be adjusted by the appropriate method given in 7.4 and 7.5, The slide with particles should be mounted on the mechanical stage of the microscope. The field of view should be adjusted by means of lamp iris to an area not much larger than that occupied by the grid and the reference circles. 8.3 Counting ProcedureAs it is not practicable to count and classify every particle on the slide, only a sample out of the total number is examined at any time. The sample is contained in a number of field 19
IS : 5258  1969 areas defined by the boundaries of the graticule grid or a sub area of it as determined by the conditions specified in 13 and 14 which are designed to take account of the errors of sampling and also to avoid counting more pa.rticles than necessary for securing an acceptable degree of precision. The conditions are different in the determination of the number and of the weight size distribution. per unit area may vary from most carefully, the field areas in which the particles present are to be counted should always be spaced out in a regular pattern in such a way that each represents an equal proportion of the total area of the slide covered by particles. The pattern used will depend on the number of fields to be counted. The procedure is illustrated in Fi,g. 3 which shows how 25 sample fields are A considered in an area of 20 mm x 20 mm on the slide. 8.3.1 As the concentration of the particles
place to place even when the slide is prepared
x
X
X
4
O4
tIit
x
X X
X
X
X
X
X
i
LENGTH
IN mm
FIG. 3
LOCATION OF SAMPLE FIELD
8.3.2 The basic technique of measurement by comparison with the reference circles on the graticule is to match them by mentally squeezing Every particle each particle into the circle of appropriate diameter. present in each field area is examined individually, the focus being adjusted if necessary, and its area compared mentally with the area of the The matching process should thus be reference circles on the graticule. carried out without moving the particles from the positions which they 20
IS : 5258 1969 occupy within the rectangle of the graticule. A particle whose area is estimated to be smaller than that of, say, circle 5 but larger than that of circle 4 is assigned to the size class defined by the diameter of the circles 4 and 5 and so on for other size classes. The transparent particles are compared with the open circles and opaque particles are compared with the solid circles. In order to avoid counting the same particle twice when sizing in adjacent areas, all the particles are recorded as belonging to the field area if they lie wholly within the boundary lines of the field area and also if they are in contact, however, slightly, with the top and left hand edges of the rectangle, similarly ignoring all those touching the bottom and right hand edges as shown in Fig. 4. It is recommended that, as far as is practicable, the particles of all the size classes being examined at one magnification should be assigned to their respective classes before passing on to the next field area.
COUNTING ISOLATED FIELD
Shaded particles are included in the count. count. Unshaded particles are excluded from
FIG.4
TREATMENT OF EDGE PARTICLES
8.3.3 If particles of the sizes being considered occur only rarely, it is recommended that the sample be taken in the form of long narrow strips each 520 mm long and of width defined by the upper and lower edges of the graticule grid. This technique will be found specially useful for counting the largest 3 or 4 size classes in the determination of weight size distribution. 21
I&:52581969 9. CALCULATIONS 9.1 Size DistributionThe
size distribution shall be calculated from the number of particles m, counted in the size classes of mean size d, found in the sample areas n, a,,
where n, = number of fields examined, and a, = area of each field in mm2.
9.2 Number mr/nr a, Size Distribution The
number of particles per unit area,
for each size class shall be calculated
for all size classes obtained. is given by:
and the sum Z _!!.?_ nl 0, The percentage by number in each size class
100 (mrlfl, a,) 7y mri nT aI
P f=
9.2.1 The number percentage over or under each size class limit is obtained by summing the percentage numbers in all larger or smaller size classes as illustrated in the example given in Appendix F.
9.3 Weight z,
Size Distribution
The
number of particles per unit area and multiplied by the cube
for each size class shall be calculated mt dr3 B is c
(2,s) of the mean size.
The sum of the products for all the size classes, obtained.
Their percentage by weight in each size class is given by: 100 ( m? @I a, a,>
Qr=~m, dr3/nr a, 9.3.1 The weight percentage over or under each size class limit is found by summing the percentage weights in all larger or smaller size classes as illustrated in the example given in Appendix G.
10. STANDARD
ERROR
10.1 The expected standard error is a measure of the errors due to counting and classifying only a limited number of particles out of the total number present on the slide sample. It should be kept less than 2 percent in order that the reproducibility or the determination on different slides may be within the given limits specified in 11. 22
IS : 5258  1969 expected standard error S (PC) 10.2 Number Size Distribution The of the percentage PC by number in each size class, out of the total number in all size classes is: P,(lOOP,) ___ __6 m, J The standard error is maximum when P, = 50 and, therefore, it will always be less than 2 percent if the total number of particles of all sizes counted, C (m,) is greater than 625. s (PC) = 10.3 Weight Size Distribution The of the percentage Q., by weight in each in ail size classes, is given approximately qo_,+* expected standard error S ( f& ) size class, out of the total weight by: Jl_$
The expected standard error calculated with the help of the above formula for each size class should not exceed 2 percent. 11. REPRODUCIBILITY 11.1 The size distribution shall be measured on not less than two analysis samples. The percentage of material, in each size class, by number or by weight according to the type of size distribution desired shall be calculatFor each class the range of ed in the manner as stated in 9.2 and 9.3. these percentages shall be calculated and from these the arithmetic average The range of the of these ranges for all size classes shall be obtained. percentages for each individual class so calculated shall not be greater than the limit given in Table 8 Co1 2 for the specified number of analysis samples counted. If the range for all size classes and the average range are within the, limits set out in Table 8 the arithmetic averages of the percentages calculated for the individual analysis samples shall be taken In case the range for any size class or the as the fmal size distribution. average range for all size classes exceeds the corresponding limit given in Table 8, then not less than two further analysis samples shall be counted. In the unlikely event of having to examine more than seven analysis samples the results shall be classified into two or more groups according to the order in which the counts have been made. No such group shall The limits set out in consist of the results of less than 4 analysis samples. Table 8 should be applied to each group separately. 12. REPORTING RESULTS
12.1 Results shall be reported as percentage oversize or percentage under It shall be size, the percentage being given to the nearest one percent. clearly stated whether the results reported refer to number size distribuThe limits of size classes shall be given in tion or weight size distribution. The criteria adopted in classifying microns to two significant figures. The presence of aggregates or their constituent particles shall be stated. 23
IS : 5258  1969 appreciable number of particles of size less than 0.6 microns, if any, should be stated in reporting the results. As far as weight size distribution is concerned the presence of particles of size below 0.6 microns is of no consequence. .
TABLE ( RANGES FOR SIZE CLASSES
(Cluusc 11.1 ) NUMBEROF ANALYSIS SAMPLESCOUNTED MAXIMVM VALUE FOX RANG~OFPERCENTAQEXN ANY SIZE a&ass MAXIMUM VALUE: FOR AVERAGIE RANGEOBPERCENTAQESFORALL SIZE CLASSES ~__._h__~ Not More 5 to 8 Size than 4 Size Classes Classes (I) 3' 4 2 7 (2) 6.0 ;:o" It.", IO.5 (3) ;:o" 8':; 8.5 9.0 (4) 4.0 g:; 7.4 7.9 8.2 9 or More Size Classes
(5) 5.2 3.7 63 ;:5" 7.8
13. CONDITIONS GOVERNING THE DETERMINATION NUMBER SIZE DISTRIBUTION 13.1 The
distribution
OF THE
number size
conditions
are:
to be satisfied in determining
the
a) the standard error ( as stated in 10) of the percentage by number in each size `class shall be less'than 2 percent of the total number in all size classes, for each of the analysis samples examined; and b) samples the reproducibility of determination on two or more shall satisfy the requirements as specified in 11. analysis
The requirements in 13.1.2 `and 13.1.3 ensure that condition (a) will be satisfied and requirements in 13.1.1,13.1.4,13.1.5,13.1.6 and 13.1.7 are designed to ensure that condition (b) is also met with. 13.1.1 Control Size ClassThe size class that contains the highest percentage by number of particles shall be considered as control size class. This may usually be the smallest size class. If the most frequent size class is not known and could not be deduced from a preliminary inspection of the slide, the smallest size class present in the slide sample shall be The control size class is denoted by considered as the control size class. the subscript ` o `, the mean size of the class by d,, the number of particles
counted and classified as belonging to it by m, and the sample area from which they are drawn by no a,.
24
IS : 5258  1969
13.1.2 Minimum number of particle than 625. total Jvumber of Particles To be CountedThe total of all size classes counted and classified shall be ndt less area (the product n, a, of the number for particles of each size class shall be
13.1.3 Sample AreaThe sample nr of fields each of are a,) examined constant.
13.1.4 Minimum Number of FieldsThe number of fields n, examined for particles of the control size class shall not be less than 96. The number of fields examined for particles of any other size class shall not be less than 12 and preferably not less than 24. 13.1.5 Area of the FieldThe area a0 of each field examined for particles of the control size class shall be that corresponding to the whole This condition applies also for all size rectangular grid of the graticule. classes examined at the magnification used for the control size class. The area a, of each field examined for particles of other size classes at a different magnification shall be so chosen that the sample area n, a, remains the same as that for the control size class no a, and also that the number n, of fields exceeds 12. 13.1.6 Density of FieldsThe concentration of particles on the slide should be so adjusted when preparing it that each field of area a, contains on an average not more than about six particles of the size class being It is desirable to adjust the concentration to give about three examined. If the concentration is higher it particles per field in the control size class. is likely, for the number and area of fields specified above, that the total number of particles counted will unnecessarily exceed the minimum of 625. 13.1.7 Order of Examining the Size ClassesIt is recommended that the size classes be examined in turn starting with the control size class, which for number size distribution will usually be the smallest size class. The other size classes to be examined at that magnification should be counted and classified at the same time over the same field area and the same The magnification should then be reduced for examining number of fields. the next larger size classes. 14.
CONDITIONS GOVERNING THE DETERMINATION WEIGHT SIZE DISTRIBUTION
to be satisfied in determining the
OF THE
weight size in in
14.1 The conditions distribution are:
a) the standard error as stated in 10 of the percentage by weight each size class shall be less than two percent of the total weight all size classes, for each analysis sample examined; and 25
IS t 5258  1969
b) the reproducibility of measurements on two or more analysis samples shall satisfy requirements as specified in 11. The requirements given in 14.1.1 to 14.1.8 are designed to ensure that in most cases both these conditions are satisfied. li.l.1 Control Size Class The larkest size class which contains more than 5 percent by weight of particles shall be considered as control size class. If the largest size class containing more than 5 percent by weight is not known and cannot be identified from a preliminary inspection of the slide, the largest size class present in the slide sample shall be considered as control size class. The control size class is denoted by subscript ` 0 `, the mean size of the class by d,, the number of particles counted and classified as belonging to it by m,, and the sample area from which they are drawn by no a,, as in the case of number size distribution. 14.1.2 Minimum Number of Particles Counted in Control S'ice ClassThe number of the particles counted and classified, rpeo as belonging to control size class shall be not less than 25. In case the control size class contains more than 10 percent by weight, which is generally unlikely, the number of particles to be counted in the control size class should exceed 25. The required number of particles ` m, ' to be counted for the standard error to be less than 2 percent is given by equation given in 10.3. 14.1.3 Sample Area for the Control Size Class The sample area n, a, to be examined for particles of the control size class may be the whole area of the slide occupied by the particles or may even require the use of more than one slide. In the latter case it is essential that the two slides are prepared from the same ,analysis sample so as to be of the same density. 14.1.4 Sample Area for Other Size ClassesThe sample area n, a, which is examined for particles of size classes other than the control size class shall be equal to or greater than:
n, a, where
(
do > N,
&
8 Jf,
n,, a,, is the sample area examined
for the control size class. size class is
The
number number
concentration concentration
No in the control
!? and the ( no a0 >
ns . It is, therefore, ( > necessary during the counting of each size class to estimate the concentration Nf which will be found when counting of'the class has been completed ( see the worked out example in Appendix G ). 26
N, in the ,th class is
IS : 5258 1969
An alternative
F,=:
way of expressing
the condition is that
the
factor factor
drs ' should mc n, aZ F odo3 4x noao
be smaller than the corresponding for the control size class . The
factor F is
referred to `as the accuracy factor and is conveniently expressed in the form F=!Y%&s r fl ml 14.1.5 Minimum Number of Fields The number of fields no examined for particles of the control size class shall be not less than 96. It is recommended that the same minimum number of fields be examined for all size classes counted and classified at the magnification used for the control size class. The number n, of fields examined for particles of any size shall be not less than 12 and preferably not less than 24.
14.1.6 Area of Each FieldThe area of each field examined for particles of the control size class shall be that of corresponding to the whole rectangular grid of the graticule. The area of each field examined for other size class shall be adjusted according to the rules given in 14.1.4 and 14.1.5 and as illustrated by the example in Appendix G. 14.1.7 Density of FieldThe concentration of particles on the slide shall be so adjusted when preparing it that each field contains, on the average, not more than about six particles of the size class being examined. 14.1.8 Order of Examining the Size ClassesIt is recommended that the size classes be examined in turn starting with the control size class which for weight size distribution will usually be the largest size class. Also, it is recommended that not more than the next three smaller size classes The magnification should then be be examined at the same magnification. increased for examining the next smaller size classes.
APPENDIX ( czuuse 0.3 )
CORRELATION Al. Al.1 GENERAL
A
METHODS
OF RESULTS FROM DIFFERENT OF SIZE DETERMINATION
A number of methods are described for the determination of particles size in the range l1 000 microns. These are the microscope, elutriation, sedimentation and test sieving (IS:4601962*). AS no single method is ~.~_ *Specification for test sieves ( raked ).
27
IS : 5258  1969 applicable to the whole range of sizes I 1000 microns, it is necessary to combine the analysis by two or more different methods in order to establish the distribution in full. In general a particle size determination will consist of a sieving of the material down to 75 microns combined with an analysis of the fraction below that size by one of the other three methods. In the size determination, what is measured is not the particle size directly but only some sizedependent property of the particle. In the microscope method it is the enlarged image of the particle, in sieving it is the ability of the particle to pass through an aperture of given size, in sedimentation it is the fall speed through a stationary fluid and in elutriation it is the upward velocity of a fluid necessary to prevent the particle falling, which are measured. If the particle is spherical, there is no difficulty in relating the results obtained by different methods of size determination because the same diameter will be assigned to the sphere whatever the method of size determination adopted. But, in the case of an irregular particle it is not possible to assign a diameter (or a length, breadth and thickness) which will enable its volume or surface area to be accurately determined. The size dependent properties of the particles can still be determined and it is often convenient to represent the particle not by the measured property but by a It is customary for the ` size' chosen to be the diameter of a sphere ` size'. that exhibits the same property as the particle, that is, the sphere that has the same projected area or that just pisses through the same sieve aperture or that falls at the same speed through a fluid. However, the sphere that is equivalent to a particle in regard to one size dependent property, say, projected area, is not necessarily of the same diameter as the sphere equivalent in regard to some other, property, say, free falling speed. An irregular particle is, therefore, assigned different sizes by different methods of determination and results obtained by different methods cannot be combined. directly. Further, it is to be noted that the sizedependent properties of a nonspherical particle depend on its orientation so that its size even as determined by a single method is no longer a constant of the particle. A1.2 The discrepancy between the `sizes' assigned to a particle by different methods depends on the departure of the particle from sphericity and the ` sizes ' from different methods can be combined to give nondimensional parameters known as shape factors, which serve to characterize the shape of the particle. A single shape factor does not characterize a particle exclusively and the particle has as many shape factors as there are pairs of methods of determining its size. Recommended factors are given below for use, in the absence of special knowledge, in correlating the following particle diameters: sieve aperture through which the particle just a) SieveNominal passes. b) Projected Diameter of circle of area equal to the projected area of the particle resting in its most stable position. 28
IS :.5258  1969
C) Stokes 4
Diameter of sphere which has the same density and the same free falling velocity as the particle in a fluid under identical conditions within the range of Stokes' law. values are given below:
The conversion
To Conuert
Sieve to projected Sieve to Stokes Projected to sieve Projected to Stokes Stokes to sieve Stokes to projected Example:
Multi& by
1.40 0.94 0.71 0.67 I.07 I.50
Particles which just pass a 75micron sieve have a mean projected diameter of 105 microns and a mean Stokes diameter of 70.5 microns. AL.3 These conversion factors should be applied with caution in case there is any suspicion that the particles of the powder under test are of extreme It is shapes, for example, if they have cleavage planes or are acicular. preferable to use then correlation factors which are specifically determined for the powder under test. Possible methods of establishing the factors are: a) to overlap the methods of size determination so that one or more size classes are assessed by both methods, and b) to size a sample of the material similar to the sample under test by both methods of size determination. Al.4 A numerical example a sieve analysis of a powder fraction passing a 75micron is given in Table 9 to show how the results of are combined with a microscope sizing of the IS Sieve.
APPENDIX
SIZING
( CZuuse 3.2)
B
ACICULAR
PARTICLES
Bl.
DETAILS
OF SIZING
Bl.1 The geometric mean of diameters (size obtained from microscopic area measurements) and the arithmetic mean of diameters (size obtained by unidirectional length measurements) tend to approach one another for increased number of measurements so long as the shape factor of the particles (ratio of the measured maximum to the measured minimum) does not exceed 4. The scope of the standard is, therefore, restricted to particles for which the length of the smallest rectangle enclosing the projected image does not exceed four times the breadth of the rectangle. Since the projected areas of particles of more elongated shape cannot be
29
TABLE 9
EXAMPLE
OF COMBINATION
OF SIEVE AND MICROSCOPE
SIZINGS
( Ckzus~ Al.4 )
ANALYSIS, SIEVE SIZE
SIEVE
mp ' Weight Passing Sieve as Percent of Total Sample Percent 94 80 59 45 
MICEOECOPEANALYSIS h_ Sieve DiaProjected meter EqDiameter uivalent to Projected Diameter*
Weight Un: der Size as Percent of Weight Passing 75 Micron IS Sieve Percent
COMBINED SIEVE MICROSCOPE ANALYSIS __.__*_7_Percentage `Weight Un Equivalent Percentage of of Weight Sieve DiaWeight Under Size as Oversize Percent of dersize meter Total Sample
Microns
Microns
Microns 
Percent 
Microns 210 150 105 75 53 37 27 19 13
Percent 94 8Q 59 45 39 28 18 11 6
Percent 6 20 41 55 61 72 a2 89 94
!s
210 150 105 75
JO6 75 53 37 27 19
75 53 37 27 19 18 100 86 63 40 25 14
45 39 28 18 11 6

*Use multiplying factor of 0.71 from Appendix A.
I
IS:52561969
reliably compared with those of circles, such particles should be assessed The measurement may be made, according to their lengths and breadths. by a ruler, on the projected images of the particles, the standard graticule grid or some similar rectangular grid being used to define the area of the sample fields. Alternatively a nonstandard graticule of the type shown in The graticule is ruled with reference to Fig. 5 may be constructed. rectangles in place of circles, the shorter dimensions of these rectangles being compared with the breadths and the longer dimensions with the lengths of the particles.' A suggested length to breadth ratio for the rectangles is 2 : 1.
IFIG. 5
TOOurm1 NONSTANDARD GRATICULEFOR SIZING ACICULARPARTICLES
B1.2 The particles may be grouped into classes according to their breadths. A few full determinations on an acicular material may show that particles in the different classes may have the same average length to breadth ratio, thus making it possible in such cases for the weight distribution to be determined by measurement of only either the breadth or the length instead If the powder consists of both spherical and acicular particles the of both. two types of particles may be assessed separately by the appropriate method and from the results the relative percentages of spheres and needles may be calculated.
IS : 5258  1969
APPENDIX ( Clause 4.2 )
PROCEDURE Cl. DETAILS FOR PREPARATION OF PREPARATION
C
OF ANALYSIS SAMPLE
Cl.1 Methods of preparing a sample of about 5 g in weight so that it is representative of the laboratory sample are given in IS : 4879l 968*. A few miligrams of the material from this intermediate sample is incorporated in a viscous liquid (glycerol, glycerine jelly, medicinal paraffin etc) in which the powder under test has been previously found to disperse completely. The viscous shear acts to separate the flocculates without shattering the individual particles. Care shall be taken to prevent formation of air bubbles in the liquid while incorporating the powder into it. After satisfactory mixing, a drop of suspension is removed with a dropping rod and transferred to a clean microscope slide. A microscope cover slip is then gently lowered on to it. The cover slip should not be pressed but should be carefully slid to prevent selective removal of the larger particles to the edge of the cover slip. Also, lightly greasing the underside of the cover slip around the edge helps to prevent spreading of the liquid outside the edges of the cover slip and also evaporation of the suspending liquid for a long enough time for the count to be performed.
C1.2 In case it is not possible to find a viscous liquid which may disperse the powder sufficiently well, it is necessary to use a more mobile liquid with the addition of a dispersing agent to prevent flocculation of the particles. The suspending liquid and dispersing agent will be specific to the powder under test, so that their choice is a matter of experiment and experience.
APPENDIX D ( Clauses 5.8 and 8.2 )
PROCEDURE Dl. DETAILED FOR ADJUSTMENT OF MICROSCOPE PROCEDURE
Dl.1 All the elements of the optical system should be properly aligned and they should be focussed along the optical axis. Instructions for the adjustment of projection microscopes are usually supplied by the manufacturers.
D1.2 The procedure for adjustment of bench microscopes is given below
(see Fig. 1):
*Method of subdivision of gross sample of powder used for determination size. of particle
32
IS : 5258 1969
Position the microscope horizontal. with the body tube vertical and the stage
Centre the physical source of illumination (filament or arc) to lie Centre the lamp diaphragm on the optical axis of the lamp lens. with respect to the lamp lens, Place the source at a distance of 25 cm from the microscope mirror and adjust it so that the axis through the lamp diaphragm, lamp lens and the primary source passes through the centre of the mirror of the microscope. Coloured light is sometimes useful for obtaining contrast with When a metcurry arc is used it is strongly coloured materials. extremely essential to use a filter to exclude ultra violet light in order to avoid undue irritation to the eye. Insert objective, eyepiece and substage condenser. Take the substage condenser close to its upper limit of travel and closing the substage condenser diaphragm tilt the mirror to focus an image of the physical source on the diaphragm, temporarily removing the diffusing screen of the lamp housing, if any. If the lamp lens cannot be moved for this purpose, move the whole lamp housing. Place the slide on the stage, open the substage condenser diaphragm and focus the objective on the particles. The position of focus is conveniently found by focussing first on the edge of the slide which can be found by moving the edge across the field of view while, at the same time, operating the fine focus adjustment. When immersion objective is used it should be oiled to the slide and to the substage condenser also, if the nominal numerical aperture of the objective exceeds 1.0. The oil used should have the refractive index stipulated by the manufacturer of the objective and condenser ( usually either 1.515 or 1.524). The objective should be brought slowly into contact with the oil to avoid trapping air bubbles. With the particles in focus, close the lamp iris partially and focus edges by racking the substage condenser up or down. Then, adjust the mirror so that the lamp iris is central in the field of view. The lamp iris will have to be closed to its smallest possible opening with high power objectives. Open the lamp diaphragm and close the substage condenser diaphragm partially. Replace the eyepiece with a pin hole cap without disturbing the focus. Place a ground glass diffusing screen immediately below the substage condenser. Bring the image of the substage diaphragm as seen through the pin whole cap concentric with the aperture stop of the objective, by means of the substage centring screws. Remove the diffusing screen and replace the eyepiece. Recentre the image of the lamp iris in the field of view as indicated in (e). 33
IS : 5256  1969
fd
Remove the eyepiece, unscrew the eyepiece lens system (positive eyepiece ) or the eye lens (negative eyepiece ) and insert the graticule so that it rests on the field stop (see Fig. 1). The eye lens should be screwed back until the graticule is in focus. The position of the focus which depends on the accommodation of the eye of observer is adjusted by alternatively looking at a distance object and through the eyepiece until, by moving the eye lens, the distant object and graticule are seen clearly without changing the accommodation of the eye. Replace the eyepiece with its graticule in the draw tube of the microscope. Adjust the length of the microscope to the setting established for the particular objective and eyepiece as indicated in Table 6. Refocus the particles and substage condenser, if necessary. Adjust the intensity and colour of illumination by means of the neutral and coloured filters. The voltage of the light source should not be altered for changing the intensity as by so doing the colour of the light also will change. The level of illumination should be low in order to reduce fatigue to the eye.
h)
APPENDIX E (Clauses 7.2, 7.5 and 7.5.1 )
CHOICE OF GRID LENGTH OF EYEPIECE GRATICULE E1. CRITERIA FOR CHOICE
El.1 Select the objectives required to cover the size range of particles present on the slide Select the eyepeice (of power x 20 or more for the
bench micrascope) which is to be used for counting and sizing and insert into it a suitable micrometer scale. Determine for each objective the magnification, from the st?ge to the plane of the eyepiece graticule, for the shortest and the longest tube length adjustment available on the microscope. Divide the measured magnification by the relative magnification of the objectives given in Table 7 according to their focal lengths. Note the largest value obtained at the shortest tube length and the smallest value obtained at the longest tube length. Multiply both values by 0.937. Select an eyepiece graticule with a grid length between the values, as illustrated in the example below. Confirm that the graticule ha&ng this size of grid can be employed with the eyepiece chosen. The length of grid shall not exceed fiveeighths of the diameter of the field stop of the eyepeice. Example: The measured magnifications at the two extreme tube lengths in the case of 4 objectives used are given in co1 2 and 3 of Table 10. The ratios of measured to relative magnification are given in co1 5 and 6 of the table. The same eyepiece x 20 was used with each objective. 34
IS : 5258  1969
TABLE 10 EXAMPLE OF CHOICE OF GRIJ.3 LENGTH FOR AN EYEPIECE GRATICULE
FOCAL LENGTH MEASURED MAONIFICATION AT PLANEOF GRATICULEFOR ~____h__~ Shortest Longest Tube Tube Length Length RELATIVE MAQNIFXCATION FnoM TABLE 7 RATIOOF MEASURED TORELATIVE MAQNIFICATIONAT ~_.___h_~_~ Longest Shortest Tube Tube Length Length
(1)
31.6 16 4.5 l9
(21
4.24 12.05 47.62 Ill*11
(3) 5,88 15.38 62.5 142.86
(4) 1 24 P 8 +/ii 16 42
(5) 4.24 4.26 4.2 1 4.91
(6) 5.88 5.43 5.53 6.32
The largest value at the shortest tube length is 4.91 (for 1.9 mm objective) and the smallest value at the longest tube length is 5.43 (for 16 mm Multiplication by O937 gives the two values 4.60 and 5.09. objective ). A graticule of grid length 4.75 mm lies within the limits. A graticule of The diameter of the field stop of the grid length up to 5 mm can be used. eyepiece lens is 10 mm and the eyepiece could accommodate a graticule of grid length up to 6.25 mm.
APPENDIX ( Clause 9.2.1)
WORKED Fl. Fl.1 EXAMPLE
F
OF NUMBER SIZE
OF DETERMINATION DISTRIBUTION OUT EXAMPLE
DETAILS
OF WORKED
It is considerably easier to determine the size distribution by number since the same total sample area is used for all size classes and also the minimum number of particles that is necessary to count, namely 625, is specified in advance. A preliminary examination of the sample slide is made to ensure that the particle concentration and the size of the sample field are such that at least 96 sample fields are examined for the control size class and at least 12 preferably 24 for any other size class.
F1.1.1 It is recommended
those particles larger than
that in counting at the highest maginification circle 7 should be recorded as such, (although 35
IS I 5258 1969 this figure is not used in the calculation number distribution) are subsequently assessed at the next lower magnification. estimates serve as a useful check over counting.
of
and these These two
F1.1.2 Also, it is recommended that with the beginning of the counting at the highest magnification an initial 25 fields be examined such that each field equals to the area covered by the graticule grid. These fields should be spaced regularly over the whole area occupied by particles. On the basis of the total number of particles, including those larger than circle 7 counted in these 25 fields, an estimate is made of the number of further fields that need to be examined to bring the number of particles counted up to 625. F1.1.3 A worked out example to show the method distribution by number is given in Table 11. of calculation of a size
APPENDIX G (Clauses 9.3.1, 14.1.4 and 14.1.6)
WORKED EXAMPLE OF DETERMINATION DISTRIBUTION OF WEIGHT SIZE
Gl. PROCEDURE Gl.1 In the determination of size distribution by weight the total sample area to be examined varies from class to class and may not be specified in advance. The counting procedure has to be controlled by various factors calculated at different stages of its determination. The following scheme is recommended in the determination of weight size distribution:
4
Preliminary ExaminationA
preliminary examination of a scan (of width equal to that of the graticule grid and lo20 mm in length) across the middle ofthe area occupied by the particles on the sample slide is made with the microscope set at the lowest magnification required, The total number of particles in the top three classes occurring in the sample is recorded. From this the number of such scans required to give a total ofabout 150 particles in the top three classes is estimated. If this estimated number is less than 5, calculate a reduced length of scan to increase it to at least 5. The count recorded in the preliminary scan is not included in the analysis proper.
b)
Analysis at Lowest MagnificationThe
number of particles counted in the top three classes are recorded from the required number of scans as decided in (a) distributing them evenly over the whole area On the basis of these figures an estimate occupied by the particles. is made to get the total sample area expected to contain 25 particles
36
IS : 5258 1969
TABLE
11
ILLUSTRATIVE
EXAMPLE
OF c~cULATION
OF SIZE DISTRIBUTION
BY NUMBER
(&4.w F1.1.3)
OBJECCIRCLE NUMBERS SIZE CLASS
LIMITS
AREA OR TEE SAMPLE FIELD (+)
NUMBER SAldO;LE FIELDS (%)
TOTAL SAMPLE AREA (% at.)
NVBXBER OB PARTICLES COUNTED IN CLASS (mc)
NUMBER OB CONCENTRATION IN CLASS
NUMBER PERCENT IN CLASS

NUMBER OF S ' DISTRIBUTIO z Pew&t
B
STANDARD ERROR PERCENT
(Nr=nsJ
(8)
( per mm* )
(1)
(2)
(3)
(microns )
(4)
mms
(5)
(6)
mms
(7)
(9)
( per mm* ) ( microns )
(12)
l&3 mm (0.25)
>37 37 27 27 19 19 13 13 9.4 [76 I 65 76 F ,65
9.46.6 6.64.7 4.73.3 3.32.3 2*31.7* 1.7l2 1.2 0.8 080.6*
0 0.054 875 &x24
O164 6
:t ii 46 52
11: 140
2!6 3.2 4.3 ;:";
j?: 19 13 69:;
0.59 0.65 0.75 0.84
0.90
45 mm ( O65 )
0.003 429 7
48
0.164 6
188 237 279 316 352 383 437 492 571 887 BNT=4 397
7.2 8.0 9":; 11.2 13.0 20.2
100.0
4.7 3.3 2.3 ;:; ::"6
0.96
1.01 1'05 1.11 1.17 1.25 1.49
1.9 mm ( 1.3 )
54 i 43
:i
0.000 857 42
192
0.164 6
72 81
,
1C Ibn+724
Column totals
*Control size class.
Standard error of control size class due to sampling = s (P, ) = 20.2 x 79.8 ___ = 724 1.49 percent [ scc 10.21
As in the Original Standard, this Page is Intentionally Left Blank
IS : 5258  1969
of the top class. Similarly on the above basis the total sample areas necessary for the second and third classes are estimated. After this estimation further necessary counting is carried QU! distributing the areas regularly. Calculate the accuracy factors F to ensure that those of the second and third classes are smaller than Fl. If it is found subsequently that more than 10 percent by weight of the material is in the top c!ass, 25 particles in the top class will not have produced the desired accuracy and further counting is necessary.
c)
The magnification is increased by, say, a factor 2 and the areas to be counted to get the desired accuracy for another 3 classes are assessed. For this purpose 25 fields are examined initially using the whole grid area for the 3 classes (or the whole grid area for the largest class and onehalf of the grid area for the other two classes) On the basis of the numbers without changing the magnification. .N, recorded in these counts decide what further area needs to be examined for each class. After completion of the counting of the minimum number of required areas for each class, calculate Fr for each class to ensure that it is less than Fl. Similar procedure is repeated by changing to the next higher magnification for other size classes. When the accuracy factor Fr for each size class has been reduced below FI calculate the weight size distribution (see 9.3). Check that the standard error due to sampling of the percentage weight in the control size class is less than 2 percent. The process is illustrated by the worked example given under G2.
4
e) G2.
WORKED
EXAMPLE
G2.1 On preliminary examination it is found that 5 scans will yield about 150 particles in the top three size classes occurring in the sample. Initial number of scans at lowest =5 in initial =5x 10x0.439 = 21.95 mm2 recorded: 106  75 microns 75  53 microns 53  37 microns The total number of particles the condition in (a) above. observed are more than 12 56 169 150 to satisfy
magnification Total area scans Number inspected
of particles
IS : 5258  1969 G2.2 Calculation of Father Top Three Classes Mean diameter of the top class Mean diameter of the second class Mean diameter class class of the third in top Scanning Area Required = d1 =I d = ds 12 =?i?K z $547/mm* 1 To ensure that the standard error due to sampling is not greater than 2 percent 2.5 particles of the top class should always be observed (see 14.1) . Therefore, estimated sample area = 21.95 x 25 12 = 45.7 mm3 = 111 a1 Number of scans required 5 X 45.7 =CE = 10.4, say 11 scans (of which 5 have already been carried out ) Similarly for the second class: Number concentration ==$&=2*551/mm* Nn Mean diameter of second class Mean diameter of top class . for These
Number concentration
Then from 14.1 the area (nz aa) to be examined for this class to ensure that standard error due to sampling does not exceed 2 percent  3 al 2.55 1 = 0.547 40 26.64 mm'
Number
of scans required
5 x 26.64 = L 2 1s95  6.1, say 7 scans.
For the third class: Number concentration 169 21.95 = 7*699/mm*
=N,
Mean diameter Mean diameter of third class of top class to ensure
s
2t
Area to be examined
the desired accuracy
=
n1
a1
(z )
=
4
6 Na
Nl
= 45.7 (&$ = 10.1 mm0 Number of scans required 5 x 10.1 21 .g5 = 2.3, say 3 scans
The count might therefore be carried out over a further minimum of 6 scans for the first class, 2 scans for the second class and no more for the third class.
G2.3 Calculation
mended 106 75 53 in Gl.1 75 microns 53 microns 37 microns
of Accuracy Factors  In the actual count as recomthe following results were obtained. 51 particles 140 particles 169 particles ( ml ) in (::%8
.
x,J
8
a
x 20 ) X 12)
( mz) ini"5;";9mmO
(ms) in (0.439 x 10 x 5) = 22.0 mm* Nl, Ns and Ns are from Table 1
G2.3.1 The corresponding number concentrations therefore O581, 2.66 and 7*70/mm* respectively.
G2.3.2 The weighting factors dr8, d$, and d$ are obtained and are 741 000, 262 000, and 92 700. 41
I6 t 5258 1969 The accuracy factors are calculated according to the equation.
Therefore 4 =
O581 x 741000 CJ
= 60 285
= the control factor Fo
Fs = 2.66 x 2621000
046 Fa= 770 x 92 700 4m
= 28911 =54911
G2.3.3 Since Fs and F3 are both less than Fl sufficient particles have been counted in the second and third classes to ensure the desired accuracy. The process is repeated at the three higher magnifications and the weight size distribution calculated as shown in Table 12.
42
IS : 5258 1969
BY WEIGHT
TABLE
12
ILLUSTRATIVE
EXAMPLE
OF CALCULATION (Claw G2.3.3 )
OF SIZE
DISTRIBUTION
OBJECTlVEf/ (NUMERICAL
CIRCLE
NUMBERS
SIZECLASS LIMITS
AREA OF SAMPLE FIELDS (4
NUMBER OFSAMPLE FIELDS
TOTAL SAMPLE AREA
NUMBER OF PARTICLES
NUADER CONCENTRATION
WEICHTINQ FACTOR
RELATIVE
WEIDHT
ACCURACY
FACTOR FOR CLASS
WEIQHT TION
SIZE
STANDARD
WEIGHT
PERCENT IN CLASS
DISTRIBU
ERROR
PEROENT
h a,)
APERTURE)
bl)
(1)
(`4
(3) microns
(4) mm'
(5)
(6)
mm'
(7)
(8)
per mm*
(9)
(IO\
("1
(`2)
(13) microns
(14)
(15)
31.6 mm
(0.10 )
106  75* 75  53 53  37 37 27 19 13  27  19  13  9.4
0.439 x 10 x 20 0.439 x 10 x 12 0.439 x 10 x 5 0.054 875 >, ,a ,> 0.003 429 7 >> 0.060 857 42 >> >, >, >>
200 120 50 100 2: 25 50 50
87.8 52.7 22.0 5.49 2.74 2.74 1.37 0.171 0.171 0.02 1 4 0.021 4 0.021 4 0.02 1 4 0.0214
51 :z 76 1:; 124
0.58 1 2.66 7.70 13.8 30.3 50.0 w5 99.4 152 159 192 220 243
741000 262 000 92 700 32 800 11600 4 100 1450 512 181
430 52 1 696 920 713 790 452 640 351480 205 000 131225 50 893 27 512 10 176 4 358 1 760 688 262
14.0 22.6 23.2 14.7 11'4 6.7 4.3 1.7 0.9 0.3 0.1 i:",! 0.01 99.99
60 285 58911 54 907 51763 38 580 17521 I1 780 12 344 5 396 1 745 681 257
75 3": 27 19 13 9.4 i:;
100~00 86.00 63.40 40.20 25.50 14.10 7.40 3.10 1.40 0.50 0.20 0.10 0.04 0.02 0.01
1.66 1.41 1.31 1.42 1.10 0.53 0.37 0.41 0.17 0.05 0.02 0.01 0.003 O*OOl
16.3 mm ( 0.25 )
4.5 mm ( 0.65 )
9.4  6.6 6.6  4.7 4.7 3.3 2.3 1.7 1.2 totals size class.  3.3  2.3  1.7  1.2  0.8
1.9 mm ( 1.3)
z 25 25 25
z.7 8.00 2.83 1.00
;:; 1.7 ;:;
Column
Cm,= 1063 S.N,= 1523
Z NrdT3 = 3 077 225
*Control
size class due to sampling S (Q 0) = d/51
Standard
error of control
43