1、BRITISH STANDARD BS 5551-2.5: 1989 ISO 7742:1988 Fertilizers Part 2: Sampling Section 2.5 Method for reduction of samples of solid fertilizers ISO title: Solid fertilizers Reduction of samples UDC 631.8:543.05:620.113:620.115.2BS5551-2.5:1989 This British Standard, having been prepared under the dir
2、ectionof the Chemicals Standards Committee, was published under the authority ofthe Board of BSI and comes intoeffect on 28 February 1989 BSI 10-1999 The following BSI references relate to the work on this standard: Committee reference CIC/37 Draft for comment 82/51689 DC ISBN 0 580 17167 1 Committe
3、es responsible for this British Standard The preparation of this British Standard was entrusted by the Chemicals Standards Committee (CIC/-) to Technical Committee CIC/37 upon which the following bodies were represented: Association of Public Analysts Department of Trade and Industry (Laboratory of
4、the Government Chemist) Fertiliser Manufacturers Association Ltd. Institute of Trading Standards Administration Ministry of Agriculture, Fisheries and Food Amendments issued since publication Amd. No. Date of issue CommentsBS5551-2.5:1989 BSI 10-1999 i Contents Page Committees responsible Inside fro
5、nt cover National foreword ii 1 Scope 1 2 Normative references 1 3 Principle 1 4 Apparatus 1 5 Procedure 2 6 Precautions 2 7 Further reduction 3 8 Sample division 3 Annex A (normative) Alternative methods 4 Annex B (informative) Examples of apparatus 5 Figure B.1 Rotating sample dividers 5 Figure B.
6、2 Riffle sample divider 6 Publications referred to Inside back coverBS5551-2.5:1989 ii BSI 10-1999 National foreword This Section of BS5551has been prepared under the direction of the Chemicals Standards Committee. For some years the United Kingdom has participated in the standardization of methods
7、of sampling fertilizers through Subcommittee2, Sampling, of Technical Committee134, Fertilizers and soil conditioners, of the International Organization for Standardization (ISO). As international agreement is reached on the methods, it is proposed to publish them as Sections of BS5551. The standard
8、 is published in four Parts, each Part being subdivided into Sections and, where appropriate, Subsections. The four Parts are: Part 1: Terminology and labelling; Part 2: Sampling; Part 3: Physical properties; Part 4: Chemical analysis. This Section of Part2is identical with ISO7742:1988 “Solid ferti
9、lizers Reduction of samples”. Terminology and conventions. The text of the International Standard has been approved as suitable for publication as a British Standard without deviation. Some terminology and certain conventions are not identical with those used in British Standards; attention is drawn
10、 especially to the following. The comma has been used as a decimal marker. In British Standards it is current practice to use a full point on the baseline as the decimal marker. Wherever the words “International Standard” appear, referring to this standard, they should be read as “Section of BS5551”
11、. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Cross-references International Standard
12、 Corresponding British Standard BS 5551 Fertilizers ISO/TR 7553:1987 Section 2.7:1988 Recommendations for minimum mass of increment of a solid fertilizer to be taken to be representative of the total sampling unit (Identical) ISO 8397:1988 Section 3.5:1988 Method for determination of particle size d
13、istribution by test sieving (Identical) Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages1 to 6, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indica
14、ted in the amendment table on the inside front cover.BS5551-2.5:1989 BSI 10-1999 1 1 Scope This International Standard specifies a method suitable for the reduction of a sample of a solid fertilizer to a smaller quantity such as may be used for analysis or for further reduction after suitable commin
15、ution. By choosing suitable equipment, the method is applicable to the reduction of a sample of any mass above a minimum defined by the size and number of particles. The method can be applied to the division of samples into a number of equally representative sub-samples. Other reduction devices and
16、methods are described in Annex A but they are not as accurate as the recommended procedure. This International Standard does not include information on the methods of obtaining the original sample. 2 Normative references The following standards contain provisions which, through reference in this tex
17、t, constitute provisions of this International Standard. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent edit
18、ions of the standards listed below. Members of IEC and ISO maintain registers of currently valid International Standards. ISO/TR 7553:1987, Fertilizers Sampling Minimum mass of increment to be taken to be representative of the total sampling unit. ISO 8397:1988, Solid fertilizers and soil conditione
19、rs Test sieving. 3 Principle Passage of the material through a rotating sample divider; collection of the fractions, followed by rejection or recombination of some of the fractions. 4 Apparatus 4.1 Basic requirements Rotating sample dividers are of several basic types. They may operate by collecting
20、 increments from a falling stream (cutter type) or by extracting a helical ribbon from a falling cylindrical curtain, such as is created by allowing the fertilizer to fall on to the apex of a cone distributor. In the case of the cutter type, each increment shall consist of a complete cross-section o
21、f the stream. All sample dividers shall conform to the following basic requirements: a) The effective opening of the cutter or slot shall be at least three times, but preferably five times, the maximum particle size of the fertilizer to be divided. In practice, this means a minimum dimension of at l
22、east15mm. b) The divider shall be constructed and operated in such a manner that every particle has an equal opportunity of being included in the sub-sample. Provided that all parts of the stream are sampled in due proportion, an unbiased sample should be obtained. c) At least50to60increments shall
23、be taken from the gross sample at each stage of division. 4.2 Test for bias The sample divider is considered acceptable for a certain type of fertilizer only after it has been installed and has been shown to comply with the test requirements for bias and precision. The tests should be based on the p
24、article size distribution of the fertilizer (see ISO8397) as this is likely to be the property most sensitive to bias. Thus, it is likely that errors in chemical analysis may themselves arise from errors in the particle size distribution of the fertilizer. At least three sieves should be used in the
25、 particle size analysis, giving at least four different fractions, none of which should contain less than5% or more than40% of the total. The particle size distribution of two analysis samples collected from each of ten gross samples from the same fertilizer is obtained by sieving through at least t
26、hree sieves. The mean difference between the percentages retained on the smallest of the sieves used is calculated and used to estimate the errors of sample division. To provide an unbiased estimate, the two analysis samples shall be as independent as possible. To do this, two separate samples shall
27、 be obtained at the one stage of division, if necessary by sampling the discarded material. The estimation of the errors of sample division is itself liable to error. The most satisfactory procedure is therefore to test the results to ensure that the errors are not greater than permitted. For exampl
28、e, if the mean difference between ten duplicate preparations is and is the estimated variance of the set of ten differences, must be smaller than0,72S d . If two successive sets of ten duplicate preparations satisfy this condition, it may be assumed that the division is satisfactory. d S d 2 dBS5551
29、-2.5:1989 2 BSI 10-1999 4.3 General description The sample divider shall be fed from a hopper fitted with one of a series of interchangeable orifices so that the time taken for the sample to flow out is about1min. The hopper may be on the vertical axis of the receiver, feeding via the distributing c
30、one, or off-centre when no such cone is needed. The standard divider operates at a rotational frequency of60min 1but this rotational frequency can be increased up to360min 1 , the variance of the sample division being reduced as a larger number of increments is taken. However, care is needed to ensu
31、re that there is no bias because of larger particles bouncing on the rapidly moving edges of the sample receiver. Examples of rotating sample dividers are shown in Figure B.1. 5 Procedure Follow the procedure specified in5.1, or5.2 or5.3, depending on the mass of the bulk sample. 5.1 Bulk sample is
32、small enough for the apparatus to handle the whole quantity in one pass 5.1.1 Set the rotating sample divider in motion and allow time for it to reach its steady rotational frequency (a period of15to20s is normally sufficient). Fill the feed hopper with the sample and open the retaining device at th
33、e base of the hopper. Top up the hopper from the remainder of the sample, making sure that at no time can material run directly from the sample container through the hopper outlet. Continue until the whole of the sample has been passed through the divider. 5.1.2 Depending on the size of the reduced
34、sample required, take and combine an appropriate number of the fractions produced by the divider and discard the remainder. 5.1.3 Repeat steps5.1.1 and 5.1.2 on the combined fractions if further reduction is needed. NOTESee clause7 and the note to5.2.4 before carrying out any further reduction. 5.2
35、Sample is too large for the apparatus to handle in one pass 5.2.1 Set the rotating sample divider in motion and allow time for it to reach its steady rotational frequency (a period of15to20s is normally sufficient). Fill the feed hopper with the sample and open the retaining device at the base of th
36、e hopper. Top up the hopper from the remainder of the sample, making sure that at no time can material run directly from the sample through the hopper outlet. Continue until the collecting devices are about80% full. 5.2.2 Depending on the size of the reduced sample required, take and combine an appr
37、opriate number of the fractions produced by the divider and place them in a covered container. Discard the remainder. 5.2.3 Repeat steps5.2.1 and5.2.2, adding the selected fractions to the container and discarding the remainder, as often as is necessary to reduce the whole of the bulk sample. 5.2.4
38、If further reduction of the material collected as in5.2.1 to5.2.3 is required, repeat step5.1 or5.2 as appropriate. NOTEProvided that a rotating sample divider is used throughout for the reduction, it is not necessary to mix the material passed through, before further reduction as in5.1.3 or5.2.4. 5
39、.3 Sample is too large for the apparatus to handle in one pass and masses of the fractions produced differ from each other by more than3 % 5.3.1 Divide the original sample into n equal parts by weighing (n = M/m, where M is the total mass of the original sample and m is the capacity of the divider).
40、 5.3.2 Pass the first of the n parts through the divider as in5.1. 5.3.3 Take a number of the fractions depending on the mass of reduced sample required and the variation between the fractions. Place this (or these) fraction(s) in a covered container and discard the remainder. 5.3.4 Repeat steps5.3.
41、2 and5.3.3 on the remainder of the n parts, adding the selected fractions to the container. The masses of the portions collected from the n operations of5.3.3 should be as nearly as possible equal to each other. 5.3.5 If further reduction of the material collected in5.3.4 is needed, repeat the proce
42、dure described in5.1, 5.2 or5.3 as appropriate. NOTEProvided that a rotating sample divider is used throughout for the reduction, it is not necessary to mix the material passed through, before reduction as described in5.1.3, 5.2.4 or5.3.5. 6 Precautions 6.1 Ensure that all equipment is clean and dry
43、 before use. 6.2 Carry out all the operations described in clause5 as rapidly as possible to avoid loss or gain of moisture.BS5551-2.5:1989 BSI 10-1999 3 6.3 Store samples in airtight containers except during the actual process of reduction. 7 Further reduction The procedures described in clause5 ca
44、n be applied to all samples, provided that the final sample mass is greater than the minimum recommended. Information on the minimum mass of the final sample for various purposes may be found in ISO/TR7553. Reduction below this minimum mass is not recommended without comminution. Thus sample reducti
45、on below this mass may not be permitted if certain physical tests (for example particle size analysis, bulk density, etc.) are to be carried out. A further reduction should only be carried out after due consideration of the nature of the material and the tests to be performed. 8 Sample division If i
46、t is required to produce a number of equally representative final samples from one sample, the same procedures (clause5 or Annex A) may be followed except that in5.1.2 or5.2.2 the fractions are not combined and may be kept separately. Rotating sample dividers normally produce six, eight or ten fract
47、ions. Various combinations and subsequent division can provide virtually any number of sub-samples with a minimum of residue.BS5551-2.5:1989 4 BSI 10-1999 Annex A (normative) Alternative methods A.1 General If a rotating sample divider as described in clause4 is not available, or cannot be used for
48、lack of power supply, it is still possible to effect reduction of samples. The two procedures described in A.2 andA.3 are known to be less precise and may introduce bias. The extent of this bias will depend on the nature of the fertilizer and the tests which are subsequently to be carried out. For e
49、xample, the standard deviations for the results of particle size analysis of replicate samples obtained by the three methods of reduction described are in the following approximate ratios: rotating divider: riffle divider: coning and quartering = 1 : 1,5 : 3,5. A.2 Riffle divider A riffle divider is a two-way divider without moving parts. It consists of a hopper having two vertical sides and two sloping sides which run the full length of the riffle divider. The hopper feeds a series of at least12rectangular slots, each having a width of at least twi
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