1、BRITISH STANDARD BS718:1991 Specification for Density hydrometersBS718:1991 This British Standard, having been prepared under the directionof the Laboratory Apparatus Standards Policy Committee, was published underthe authority of the Standards Board and comes into effect on 31 May1991 BSI 06-1999 F
2、irst published December 1936 Second edition April 1953 Third edition December 1960 Fourth edition December 1979 Fifth edition 1991 The following BSI references relate to the work on this standard: Committee reference LBC/5 Draft for comment 90 54510 DC ISBN 0 580 19529 5 Committees responsible for t
3、his British Standard The preparation of this British Standard was entrusted by the Laboratory Apparatus Standards Policy Committee (LBC/-) to Technical Committee LBC/5, upon which the following bodies were represented: British Laboratory Ware Association Department of Trade and Industry (Laboratory
4、of the Government Chemist) Department of Trade and Industry (National Physical Laboratory) Department of Trade and Industry (National Weights and Measures Laboratory) Institute of Brewing Institute of Petroleum National Sulphuric Acid Association Royal Society of Chemistry Scotch Whisky Association
5、Society of Glass Technology Amendments issued since publication Amd. No. Date CommentsBS718:1991 BSI 06-1999 i Contents Page Committees responsible Inside front cover Foreword iii 1 Scope 1 2 References 1 3 Basis of scale 1 4 Reference temperature 1 5 Surface tension 1 6 Reference levels for adjustm
6、ent and reading 1 7 Immersion 1 8 Materials and workmanship 1 9 Form 2 10 Scale 2 11 Ranges of the series of hydrometers 3 12 Principal dimensions 3 13 Maximum permitted instrument errors 4 14 Inscriptions 4 Appendix A Standard categories of surface tension for hydrometers 5 Appendix B Meniscus corr
7、ections 6 Appendix C Recommended stem diameters for hydrometers 7 Appendix D Testing of BS hydrometers 8 Appendix E Method for determination of density by means of BS hydrometers 8 Appendix F Table for use in calculating quantities of liquid in bulk 12 Appendix G Vessels for hydrometer observations
8、13 Appendix H Density of air-free distilled water 13 Appendix J Differences between readings on hydrometers graduated on various bases of scale 16 Figure 1 Preferred design of hydrometer bulb 2 Figure 2 Examples of hydrometer scales permitted in clause10 17 Figure 3 Overflow vessels suitable for obs
9、ervations on hydrometers 18 Table 1 Principal requirements for series of hydrometers 4 Table 2 Maximum permitted instrument errors 4 Table 3 Standard categories of surface tension 5 Table 4 Average meniscus corrections expressed in units of density 6 Table 5 Average meniscus corrections expressed in
10、 units of length 7 Table 6 Recommended stem diameters for hydrometers 7 Table 7 Corrections for temperature applicable to BS density hydrometers standardized at20 C or15 C 10 Table 8 Surface tension corrections 11 Table 9 Conversion of density (kg/m 3or g/ml) to apparent mass (in air) in kg or g of
11、the liquid occupying1m 3or1ml at a given temperature, t 12 Table 10 Cylinders complying with the requirements of BS604 suitable for observations on BS hydrometers 13 Table 11 Density of air-free distilled water (kg/m 3 ) 14BS718:1991 ii BSI 06-1999 Page Table 12 Differences between readings on hydro
12、meters graduated for density at20 C or15 C or relative density60/60 F 16 Publication(s) referred to Inside back coverBS718:1991 BSI 06-1999 iii Foreword This British Standard has been prepared under the direction of the Laboratory Apparatus Standards Policy Committee. It supersedes BS718:1979 which
13、is withdrawn. BS718:1979 was undertaken with the following objectives in view. a) To align as nearly as practicable with ISO387 and ISO649 prepared by Technical Committee48, Laboratory glassware and related apparatus, of the International Organization for Standardization (ISO). b) To restrict the sc
14、ales of density to the exclusion of relative density (formerly termed specific gravity) 1) . c) As a step to the full utilization of basic SI units, to introduce the option of scales marked in kg/m 3as an alternative to g/ml. In addition to the five series and two sub-series of hydrometers specified
15、 in the1960 edition, a new sub-series (S50SP) was introduced which, like the other sub-series, is for use in the petroleum industry. This edition introduces technical changes but it does not reflect a full review or revision of the standard which will be undertaken in due course. This edition introd
16、uces an additional single range hydrometer in the sub-series particularly for use with petroleum fuels and updates the data for density of water inAppendix H to allow for changes in the International Temperature Scale in ITS-90. In addition to the specification this standard contains a number of app
17、endices. These include a table of the surface tension categories adopted for the hydrometers, a table of recommended stem diameters, information on the technique for using hydrometers, tables of temperature corrections, indications of the influence of surface tension on the various hydrometers, a ta
18、ble for correcting readings taken at the top of the meniscus in opaque liquids and tables facilitating the measurement of the volume of liquid in bulk on the basis of hydrometer observations 2) . Suitable vessels for use with the hydrometers are described. The relationship between density and weight
19、 per millilitre in air is indicated. A new table for the density of distilled water between0 C and40 C is included. Information enabling hydrometer and pyknometer readings to be interrelated (given in the1960 edition of this British Standard) is given in BS733. Guide to intending purchasers of Briti
20、sh Standard hydrometers The following notes are provided to assist in the selection of the particular British Standard hydrometers which are the most suitable in any given circumstances. Intending purchasers are advised to state precisely, when enquiring or ordering from suppliers, which of the vari
21、ants referred to are required. The references on the right are to the relevant portions of the standard. 1) Users who may have a continuing need to use relative density (d 60/60F) hydrometers should refer to ISO650 which is technically identical with the relevant parts of the1953 and1960 editions of
22、 this standard. 2) Attention is drawn to the fact that in the petroleum industry a different method, of special applicability, is in use for the measurement of oil in bulk.BS718:1991 iv BSI 06-1999 A British Standard does not purport to include all the necessary provisions of a contract. Users of Br
23、itish Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. a) Series (which governs the size of the hydrometer and the precision of readings) Reference Series Nominal range of individual scales Scale su
24、bdivision Total length Table 1 and Table 2 L20 L50 or L50SP M50 or M50SP M100 S50 S50SP (long) (long) (medium) (medium) (short) (short) kg/m 3 20 50 50 100 50 50 g/ml 0.020 0.050 0.050 0.100 0.050 0.050 kg/m 3 0.2 0.5 1.0 2.0 2.0 1.0 g/ml 0.0002 0.0005 0.001 0.002 0.002 0.001 mm 335 335 270 250 190
25、190 b) Range of hydrometer required. Selection to be made according to application and range required from the70 hydrometers in series L20, the28 in series L50, M50 or S50, and the14 in series M100; or from the11 covering the range0.6g/ml to1.1g/ml in sub-series L50SP, M50SP or S50SP. Clause11 c) Ba
26、sis of scale. For sub-series L50SP, M50SP and S50SP only, select density at15C or density at20C. Clause3 d) Surface tension category. Select low or medium or high according to the type of liquid and the method of use or for hydrometers of the highest precision, specify the liquid in which they will
27、be used. Clause5 e) Special requirements, where unavoidable, in accordance with the particular circumstances. For example, a smaller maximum error than that specified in the standard may be essential; or it may be that the hydrometer will be used at a temperature higher than70C, in which case either
28、 the loading material should have a softening point higher than80C, or a hydrometer with mercury loading should be used. Clause13 Clause8 It may also be desired to order special hydrometer jars appropriate to the instruments which are being purchased. Appendix G Summary of pages This document compri
29、ses a front cover, an inside front cover, pagesi to iv, pages1 to 18, 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.BS718:1991 BSI 06-1999 1
30、1 Scope This British Standard specifies requirements for five basic series of glass hydrometers of constant mass which are graduated to indicate density (kg/m 3or g/ml) when used at20 C. Each series comprises hydrometers which between them cover the interval600kg/m 3 to2000kg/m 3 (0.6g/ml to2.0g/ml)
31、. The hydrometers are graduated appropriately for use in liquids of low, medium or high surface tension. The standard also specifies three sub-series of hydrometers which are graduated either to indicate density when used at15 C or to indicate density when used at20 C. They have smaller tolerances o
32、n scale error, are limited to the range600kg/m 3to1100kg/m 3 (0.6g/ml to1.1g/ml) and are for use in liquids of low surface tension. A single hydrometer principally suitable for the measurement of the density of petroleum fuels is included. This British Standard does not cover hydrometers with a buil
33、t-in thermometer (thermohydrometers). 2 References The titles of the publications referred to in this standard are listed on the inside back cover. 3 Basis of scale 3.1 The basis of scale shall be density (mass per unit volume) in kilograms per cubic metre (kg/m 3 ). The use of grams per cubic centi
34、metre (g/cm 3 ) or grams per millilitre (g/ml) is accepted. NOTEThe term millilitre (ml) is commonly used as a special name for the cubic centimetre (cm 3 ), in accordance with a decision of the twelfth Confrence Gnrale des Poids et Mesures. The term millilitre is acceptable, in general, for referen
35、ce to capacities of volumetric glassware and is used in the present text. 4 Reference temperature 4.1 The standard reference temperature for density hydrometers excluding the special sub-series L50SP, M50SP and S50SP shall be20 C. When used in a liquid at this temperature, the hydrometer shall indic
36、ate the density of the liquid at20 C. 4.2 The standard reference temperature for density hydrometers of the special sub-series L50SP, M50SP and S50SP shall be either15 C or20 C. When used in a liquid at the appropriate temperature, the hydrometer shall indicate the density of the liquid at that temp
37、erature. 5 Surface tension The adjustment in manufacture shall be related to specific capillary conditions as follows. 5.1 When the hydrometer is slightly displaced from its equilibrium position in a liquid, the stem passes through the liquid surface without causing any apparent alteration in the sh
38、ape of the meniscus. 5.2 The hydrometer scale shall be adjusted either for a given liquid having a given surface tension or for one of the standard categories of surface tension given in Appendix A. Except where the highest precision is required, one of the standard categories of surface tension giv
39、en in Appendix A shall be used. For hydrometers of the highest precision, intended for use in particular liquids (e.g.alcohol solutions), the surface tension values appropriate to clean surfaces of these liquids and to the actual indications of the hydrometer shall be used: see14.2 c). 5.3 The sub-s
40、eries L50SP, M50SP and S50SP are limited to the low surface tension category. 6 Reference levels for adjustment and reading 6.1 The scales of the hydrometers shall be adjusted for readings taken at the level of the horizontal liquid surface. NOTEIf a hydrometer having a scale so adjusted is used in
41、an opaque liquid, readings may be taken at the top of the meniscus where it appears to meet the stem, but an appropriate correction to the level of the horizontal liquid surface should then be made. (SeeAppendix B.) 6.2 The middle of the thickness of a scale line shall be taken as its definitive pos
42、ition. 7 Immersion Hydrometers shall be graduated for use with the emergent stem dry, except in the immediate vicinity of the meniscus. 8 Materials and workmanship 8.1 The bulb and the stem shall be made of a suitable transparent glass selected and processed to be as free as possible from stress and
43、 visible defects, and having a thermal cubical expansion coefficient of (25 2) 10 6 C 1 . NOTEThe value of the thermal cubical expansion coefficient conforms with the conventional value quoted in ISO1768 for use in the preparation of measurement tables for liquids.BS718:1991 2 BSI 06-1999 8.2 The lo
44、ading material shall be fixed in the bottom of the hydrometer. After the finished hydrometer has been kept in a horizontal position for1h at80 C, or any higher temperature at which the hydrometer is intended to be used, and subsequently cooled in that position, the instrument shall meet the requirem
45、ents of9.3. 8.3 There shall be no loose material in the instrument. 8.4 The strip on which the scale and inscriptions are marked shall have a smooth matt surface. The strip shall show no evidence of charring. The strip bearing the scale shall not become discoloured or distorted when the stem is expo
46、sed for1h to a temperature of80 C, or any higher temperature at which the hydrometer is intended to be used. 9 Form 9.1 The outer surface shall be symmetrical about the main axis. 9.2 There shall be no abrupt changes in cross section. The tapered design shown in Figure 1 is preferred, but any design
47、 which does not permit air bubbles to be trapped is acceptable. 9.3 The hydrometer shall float with its axis vertical to within1.5 of arc. 9.4 A thermometer shall not form part of the hydrometer. 10 Scale Examples of recommended scales for BS hydrometers are illustrated in Figure 2. 10.1 General 10.
48、1.1 The strip on which the scale and inscriptions are marked shall remain securely fastened in place at a temperature of80 C or any higher temperature at which the hydrometer is intended to be used. 10.1.2 Appropriate means shall be incorporated for ensuring that any displacement of the strip bearin
49、g the scale is readily apparent. NOTEAny displacement renders the instrument unsuitable for use. 10.1.3 The scale shall be straight and without twist. 10.1.4 No hydrometer shall have more than one type of density scale. If a hydrometer has duplicate scales, the values indicated by them shall not differ. 10.1.5 The scale lines and inscriptions should preferably be black and shall be clearly and durably marked on the strip. 10.2 Graduation lines 10.2.1 The graduation lines shall be distinct and of uniform thickness not
