1、BRITISH STANDARD CONFIRMED JUNE 1993 BS 6049-5: 1989 ISO 1576:1988 Methods of test for tea Part 5: Determination of water-soluble ash and water-insoluble ash ISO title: Tea Determination of water-soluble ash and water-insoluble ash UDC 663.95:543.822:543.831:001.4:620.1BS6049-5:1989 This British Sta
2、ndard, having been prepared by the Food andAgriculture Standards PolicyCommittee, was publishedunder the authorityofthe Board of BSI andcomes into effect on 28April1989 BSI 12-1999 First published December 1980 First revision April 1989 The following BSI references relate to the work on this standar
3、d: Committee reference FAC/8 Draft (ref. 88/52908) announced inBSI News July 1988 ISBN 0 580 17217 1 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Food and Agriculture Standards Policy Committee (FAC/-) to Technical Committee FAC/8, up
4、on which the following bodies were represented: Campden Food Preservation Research Association Department of Trade and Industry (Laboratory of the Government Chemist) Ministry of Agriculture, Fisheries and Food Overseas Development Natural Resources Institute Paper Sack Development Association Ltd.
5、Tea Producers Association United Kingdom Tea Association Amendments issued since publication Amd. No. Date of issue CommentsBS6049-5:1989 BSI 12-1999 i Contents Page Committees responsible Inside front cover National foreword ii 1 Scope 1 2 Normative references 1 3 Definitions 1 4 Principle 1 5 Appa
6、ratus 1 6 Procedure 1 7 Expression of results 1 8 Test report 2 Publications referred to Inside back coverBS6049-5:1989 ii BSI 12-1999 National foreword This Part of BS 6049 has been prepared under the direction of the Food and Agriculture Standards Policy Committee. It supersedes the1981 edition of
7、 BS6049-5, which is withdrawn, and implements an agreement, to which the UKwas a party, reached in Subcommittee8, Tea, of Technical Committee TC34, Agricultural food products, of the International Organization for Standardization (ISO). The UK also provides the Secretariat for the Subcommittee. This
8、 Part of BS6049 is identical with ISO1576:1988 “Tea Determination of water-soluble ash and water-insoluble ash”. The principal difference between this Part of BS6049 and the 1981 edition is that it is now considered that silica dishes are unsuitable for use with the test. Terminology and conventions
9、. 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 especially to the following. The comma has been used as
10、a decimal marker. In British Standards it is current practice to use a full point on the baseline as the decimal marker. The symbol “l” has been used to denote litre (and in its submultiples.). In British Standards it is current practice to use the symbol “L”. Wherever the words “International Stand
11、ard” appear, referring to this standard, they should be read as “Part of BS6049”. Additional information. With reference to6.2.1, water complying with grade3 of BS3978 “Specification for water for laboratory use” is suitable. This standard describes a method of test only and should not be referred t
12、o as a specification defining limits of purity. Reference to the standard should indicate that the method of test used is in accordance with BS6049-5. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their corre
13、ct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Cross-references International Standard Corresponding British Standard BS 6049 Methods of test for tea ISO 1572:1980 Part 1:1981 Preparation of ground sample of known dry matter content (Ide
14、ntical) ISO 1575:1987 Part 4:1988 Determination of total ash (Identical) ISO 1577:1987 Part 6:1988 Determination of acid-insoluble ash (Identical) ISO 1578:1975 Part 7:1981 Determination of alkalinity of water-soluble ash (Identical) Summary of pages This document comprises a front cover, an inside
15、front cover, pages i and ii, pages 1 and 2, 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 indicated in the amendment table on the inside front cover.BS6049-5:1989 BSI 12-1999 1 1 Scope This Internatio
16、nal Standard specifies a method for the determination of the water-soluble ash and the water-insoluble ash of tea. 2 Normative references The following standards contain provisions which, through reference in this text, constitute provisions of this International Standard. At the time of publication
17、, 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 editions of the standards listed below. Members of IEC and ISO maintain registers of cu
18、rrently valid International Standards. ISO 1572:1980, Tea Preparation of ground sample of known dry matter content. ISO 1575:1987, Tea Determination of total ash. 3 Definitions For the purposes of this International Standard, the following definitions apply. 3.1 water-soluble ash the part of the tot
19、al ash dissolved by water under the conditions specified in this International Standard 3.2 water-insoluble ash the part of the total ash remaining after treatment with water under the conditions specified in this International Standard 4 Principle Extraction of the total ash with hot water, filtrat
20、ion through ashless filter paper, ignition and weighing of the residue to determine the insoluble ash; calculation of the soluble ash by difference. 5 Apparatus Usual laboratory apparatus and, in particular, the following. 5.1 Dish, of 50ml to 100ml capacity, used for the determination of total ash.
21、 NOTEIt is considered that silica dishes are unsuitable for use with this test. 5.2 Furnace, capable of being controlled at525 C 25 C. 5.3 Steam-bath 5.4 Filter paper, ashless. 5.5 Desiccator, containing an effective desiccant. 5.6 Analytical balance 6 Procedure 6.1 Test portion Use the total ash ob
22、tained from the determination specified in ISO1575. 6.2 Determination 6.2.1 Add 20 ml of distilled water (or water of at least equivalent purity) to the total ash in the dish(5.1), heat nearly to boiling and filter through the filter paper (5.4). Wash the dish and the filter paper with hot distilled
23、 water (or water of at least equivalent purity) until the volume of the combined filtrate and washings is about60ml. Return the filter paper and contents to the dish (5.1), evaporate off the water carefully on the steam-bath (5.3), and heat in the furnace (5.2) at525 C 25 C until the ash is free fro
24、m visible carbon particles. Cool in the desiccator (5.5) and weigh. Heat again in the furnace for30min, cool and weigh, and repeat these operations, if necessary, until the difference between two successive weighings is less than0,001g. Note the lowest mass. 6.2.2 Carry out two determinations, using
25、 the residues obtained from two determinations of total ash. 6.2.3 Reserve the filtrate for the determination of the alkalinity of the water-soluble ash see ISO1578 1) . Reserve the water-insoluble ash for the determination of acid-insoluble ash seeISO1577 2) , if required. 7 Expression of results 7
26、.1 Method of calculation 7.1.1 Water-insoluble ash The percentage, by mass, of water-insoluble ash yielded by the ground sample, on the dry basis, is given by the formula where m 0 is the mass, in grams, of the test portion of the ground sample used for the determination of total ash; m 2 is the mas
27、s, in grams, of the water-insoluble ash; 1) ISO 1578:1975, Tea Determination of alkalinity of water-soluble ash. 2) ISO 1577:1987, Tea Determination of acid-insoluble ash.BS6049-5:1989 2 BSI 12-1999 RS is the dry matter content, as a percentage by mass, of the ground sample, determined in accordance
28、 with ISO1572. Take as the result the arithmetic mean of the two determinations, provided that the requirement for repeatability (see7.2) is satisfied. 7.1.2 Water-soluble ash The percentage, by mass, of water-soluble ash yielded by the sample, on the dry basis, is given by the formula where m 0 , m
29、 2and RS have the same meaning as in7.1.1; m 1 is the mass, in grams, of the total ash. 7.1.3 Percentage of water-soluble ash in total ash This percentage is given by the formula 7.2 Repeatability The difference between the results of two determinations carried out simultaneously or in rapid success
30、ion by the same analyst should not exceed0,2g of water-insoluble ash per100g of ground sample. 8 Test report The test report shall specify the method used and the result obtained. It shall also mention all operating details not specified in this International Standard, or regarded as optional, toget
31、her with details of any incidents which may have influenced the result. The test report shall include all information necessary for the complete identification of the sample.BS6049-5:1989 BSI 12-1999 Publications referred to See national foreword.BS 6049-5: 1989 ISO 1576:1988 BSI 389 Chiswick High R
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