1、BRITISH STANDARD BS734-1:1973 Incorporating Amendment No. 1 Measurement of the Density of milk using a hydrometer Part1: Specification for hydrometers for use in milk UDC 637.127:531.756BS734-1:1973 This British Standard, having been approved by the DairyingIndustry StandardsCommittee, waspublished
2、under the authorityof the Executive Boardon 29 October1973 BSI11-1999 First published May1937 First revision March1955 Second revision as PartI September1960 Third revision October1973 The following BSI references relate to the work on this standard: Committee reference DAFA/3 Draft for comment69/29
3、084 ISBN 0 580 07074 3 Co-operating organizations The Dairying Industry Standards Committee, under whose supervision this British Standard was prepared, consists of representatives from the following Government departments and scientific and industrial organizations: Chemical Society National Farmer
4、s Union Commonwealth Bureau of Dairy Science and National Institute for Research in Dairying* Technology Office of the High Commissioner for Australia* Dairy Trade Federation* Office of the High Commissioner for Department of Health and Social Security New Zealand* Department of Trade and Industry,
5、Laboratory Process Plant Association of the Government Chemist* Royal Association of British Dairy Farmers* Institute of Food Science and Technology Royal Institute of Public Health and Hygiene Milk Marketing Board* Royal Society of Health Milk Marketing Board for Northern Ireland* Scottish Milk Tra
6、de Federation Milking Machine Manufacturers Association Society of Chemical Industry Ministry of Agriculture, Fisheries and Food* Society of Dairy Technology* National Association of Creamery Proprietors United Kingdom Dairy Association* and Wholesale Dairymen West of Scotland Agricultural College T
7、he Government departments and scientific and industrial organizations marked with an asterisk in the above list, together with the following, were directly represented on the committee entrusted with the preparation of this standard: Association of British and Dominion Hannah Research Institute Cond
8、ensed Milk Manufacturers Ice Cream Alliance Ltd. Association of British Manufacturers of Ice Cream Federation Ltd. Milk Powder Joint Committee of the Milk Marketing Board Association of Butter Makers, Blenders and and the Dairy Trade Federation Packers London Provision Exchange Association of Public
9、 Analysts Ministry of Agriculture, Government of Association of Public Health Inspectors Northern Ireland British Food Manufacturing Industries Society for Analytical Chemistry Research Association University of Reading British Paper and Board Makers Association Amendments issued since publication A
10、md. No. Date of issue Comments 1963 May 1976 Indicated by a sideline in the marginBS734-1:1973 BSI 11-1999 i Contents Page Co-operating organizations Inside front cover Foreword ii 1 Scope 1 2 Scale ranges, subdivision of scales and tolerances 1 3 Adjustment 1 4 Materials and construction 1 5 Form 2
11、 6 Scales 2 7 Principal dimensions 2 8 Inscriptions 3 Appendix A Suitable hydrometer cylinders 4 Appendix B Thermometer 4 Appendix C Notes on verification of hydrometers 4 Appendix D Testing of British Standard hydrometers for use in milk 6 Figure 1 British Standard density hydrometers for use in mi
12、lk 7 Figure 2 Hydrometer scales 8 Figure 3 Cylinder for Nos.1 and1A hydrometers 9 Figure 4 Cylinder for Nos.2 and2A hydrometers 10 Table 1 Principal dimensions 3BS734-1:1973 ii BSI 11-1999 Foreword BS734 was first published, under the authority of the Dairying Industry Standards Committee, in1937 an
13、d a revised edition was published in1955. In1959 the standard was again revised; Part2 “Methods” was published in that year, and in1960, Part1, “Apparatus”. Part1 of this British Standard specifies hydrometers of two sizes to meet the need of the dairying industry to deal with milk samples of differ
14、ing volumes. Two scale ranges are provided for each size. This revision has been based on draft International Standard ISO2449, “Milk and Liquid milk products density hydrometers for use in products with a surface tension of approximately45mN/m”, to which the Nos.1 and1A hydrometers strictly conform
15、. The smaller, less precise Nos.2 and2A hydrometers, which do not appear in the ISO document, have been retained in a modified form as their use is widespread in the United Kingdom. The Nos.3 and3A hydrometers specified in the1960 edition have not, however, been retained. The basis of adjustment of
16、the hydrometers adopted in1937 was density in grams (mass) per millilitre at20 C in a liquid with a surface tension of46dyn/cm. In this revision, however, the internationally accepted value of45mN/m (see3.3,Note) for the average surface tension at20 C of freshly formed surfaces of milk has been adop
17、ted as the basis of adjustment. NOTEThe system of units known as the International System of units (SI), and adopted by ISO see BS3763, “The International System of units (SI)”, has been used in this British Standard as follows. 1) Instead of the surface tension unit “dyne per centimetre”(dyn/cm) us
18、ed in ISO R387, “Principles of construction and adjustment of hydrometers”, the unit adopted is the “millinewton per metre”(mN/m), the appropriate decimal multiple of the SI unit of surface tension “newton per metre”(N/m), where the newton (N), the SI unit of force, is defined as that force which, w
19、hen applied to a body having a mass of1kg gives it an acceleration of1m/s 2 .(1mN/m=1dyn/cm.) 2) The SI unit of density, i.e.mass per unit volume, is the “kilogram per cubic metre”(kg/m 3 ), an appropriate decimal multiple being the “gram per cubic centimetre”(g/cm 3 ). As a convenient synonym for t
20、he latter unit, the SI system allows the use of “gram per millilitre”(g/ml), and this method of expressing density, accepted in ISO R387, has been adopted. It should be noted that “density(g/ml)”, means “gram (mass) per millilitre” and not “gram (observed weight) per millilitre.”(1g/ml=1g/cm 3 .) De
21、tails of cylinders in which the hydrometers may be used are given in Appendix A, and suitable thermometers for use with them are described in Appendix B. Notes on the verification of hydrometers are given in Appendix C, with two recommended procedures for comparison with similar reference hydrometer
22、s in order to determine corrections for hydrometer errors. For the benefit of users, these methods will also be included in the revision of the1959 edition of Part2 of this British Standard BS734, “Measurement of the density of milk using a hydrometer”, Part2 1) , “Method for the determination of mi
23、lk density”. Details of the facilities available for verification of the hydrometers are given in Appendix D. 1) In course of preparationBS734-1:1973 BSI 11-1999 iii A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible
24、for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pagesi toiv, pages1to10, an inside back cover and a back cover. This standard has been updated (
25、see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.iv blankBS734-1:1973 BSI 11-1999 1 1 Scope This Part of this British Standard specifies requirements for glass hydrometers of constant mass, for use in milk having a
26、surface tension of approximately45mN/m, which indicate density in grams per millilitre and which comply with ISO387, “Principles of construction and adjustment of hydrometers”. Two sizes of hydrometer are specified, with two scale ranges for each size. The larger hydrometers, designated No.1 and No.
27、1A to distinguish between the scale ranges, correspond to the precision types specified in draft International Standard ISO2449, “Milk and liquid milk products Density hydrometers for use in products with a surface tension of approximately45mN/m”. The smaller hydrometers, designated No.2 and No.2A t
28、o distinguish between the scale ranges, are more robust instruments intended to permit the density of smaller samples to be determined. 2 Scale ranges, subdivision of scales and tolerances 2.1 Scale ranges. The scale ranges shall be as follows: 1) 1.025g/ml to1.035g/ml for the Nos.1 and2 hydrometers
29、, for use in milks of normal density; 2) 1.015g/ml to1.025g/ml for the Nos.1A and2A hydrometers, for use in milks of low density. 2.2 Sub division of scales. The scales for the hydrometers shall be sub divided at each0.0002g/ml for the Nos.1 and1A hydrometers and at each0.0005g/ml for the Nos2 and2A
30、 hydrometers. 2.3 Tolerances. The density indication of the hydrometers shall not be in error at any point on the scale by more than 0.0002g/ml for the Nos.1 and1A hydrometers, or by more than 0.0003g/ml for the Nos.2 and2A hydrometers. 3 Adjustment 3.1 Reading level. The hydrometers shall be adjust
31、ed to be read at the top of the liquid meniscus, i.e.where the meniscus appears to meet the stem see3.4 and8 2). 3.2 Immersion. The hydrometers shall be adjusted to give correct readings when the emergent stem is wetted by the liquid to a level not more than3mm above the top of the meniscus. 3.3 Tem
32、perature and surface tension. The hydrometers shall be adjusted to indicate density in grams per millilitre at20 C when floating in a liquid at20 C with a surface tension of45mN/m. NOTEThe value45mN/m is taken as the average surface tension at20 C of freshly formed surfaces of cows milk, i.e.the sur
33、face obtained by pouring milk into a vessel until some has overflowed. 3.4 Adjustment Level. A No.1 (or1A) hydrometer or a No.2 (or2A) hydrometer shall be regarded as being correctly adjusted when its reading at the level of the flat surface of a transparent liquid at20 C and with a surface tension
34、of45mN/m (seeNote1), exceeds the density of the liquid by0.0003g/ml or0.0004g/ml, respectively, values that correspond to the height of each meniscus (seeNote2). NOTE 1It is not essential for the transparent liquid used for adjustment to have a temperature of20 C and a surface tension of45mN/m provi
35、ded that appropriate corrections are applied. NOTE 2The quoted values of0.0003g/ml and0.0004g/ml were derived from a modification of Langbergs formula for meniscus height (see below), and also from experimental observations, for hydrometers whose scales and dimensions comply with the requirements of
36、 this British Standard. 4 Materials and construction 4.1 The bulb and stem of the hydrometer shall be made of transparent glass, and shall be as free as possible from strain and visible defects. In particular, the external surface shall be smooth and free from irregularities. The base of the bulb ma
37、y be strengthened by internal thickening of the wall. 4.2 The loading material shall be lead shot securely embedded in a suitable cementing material in the bottom of the bulb. The loading material shall be such that, if the hydrometer is kept in a horizontal position for one hour at40 C, it shall su
38、bsequently float with its axis within1.5 of the vertical (see5.3). 4.3 There shall be no loose material in the hydrometer. 4.4 The scale paper shall preferably be white, shall be of high quality and shall have a smooth surface that permits the graduation lines, numbers and inscriptions to be marked
39、finely and clearly on it. All scale markings shall be permanent. Where h is the meniscus height in terms of “grams per millilitre”, is the surface tension of liquid(mN/m), i is the scale range(g/ml)(i.e.0.01 for No.1,1A,2, or2A hydrometers), d is the external diameter of the stem(mm), is the density
40、 of the liquid(g/ml), and s is the mean scale length(mm) (e.g.64 for a No.1 or No.1A hydrometer).BS734-1:1973 2 BSI 11-1999 NOTEIt is recommended that the paper should be an esparto paper(65% to75% esparto is suitable) and that the scale strips should be cut with their length in the machine directio
41、n of the paper. The scale paper in a hydrometer shall show no evidence of charting and when exposed to a temperature of80 C for24h shall not become discoloured or distorted. 4.5 The scale paper shall be securely fastened in place. The scale paper shall have a scale mark, a few millimetres above the
42、top graduation line, consisting of a short horizontal line with a “V” at each end (thus:). A fine reference line of uniform thickness shall be cleanly etched on the hydrometer stem at a position coincident with the horizontal portion of the scale mark so that the ends of the etched line project into
43、 the “V” at each end of the scale mark. A hydrometer shall be deemed not to comply with the requirements of this British Standard if there is any displacement of the scale paper, i.e.if the scale mark and the reference line do not exactly coincide. 5 Form 5.1 The outer surface of the hydrometer shal
44、l be symmetrical about its axis and there shall be a smooth transition between the bulb and the stem and no other abrupt changes in cross-section. 5.2 The tapered designs shown in Figure 1 are preferred, but any similar design that does not permit air bubbles to be trapped is acceptable. 5.3 The hyd
45、rometer shall float so that its axis does not deviate by more than1.5 from the vertical position. 6 Scales Figure 2 shows the sequence and numbering of graduation lines which shall be followed, and illustrates acceptable scales. 6.1 General 6.1.1 The scale shall be straight and without twist. 6.1.2
46、There shall be no irregularities in the spacing of the graduation lines. 6.1.3 The graduation lines shall be at right angles to the axis of the hydrometer. 6.1.4 The graduation lines shall be of uniform thickness not exceeding0.2mm. 6.1.5 The scale shall extend at both ends beyond its nominal limits
47、 by at least two graduation lines. 6.1.6 All numbers shall be printed in black. 6.2 Nos.1 and1A hydrometer scales 6.2.1 The main graduation lines (density equivalent0.001g/ml) shall extend completely round the circumference of the stem, shall be numbered and shall be printed in black. 6.2.2 The mino
48、r graduation lines shall all be the same length, which shall be not less than2mm, shall extend at least one-fifth, and preferably between one-third and one-half, of the way round the circumference of the stem, and shall be printed in black, or preferably in red. 6.2.3 The ends of the minor graduatio
49、n lines shall lie vertically above one another. 6.2.4 The numbers representing the nominal limits of the scale shall be written in full, and the remaining numbers shall be indicated by the second and third decimal digits only. 6.2.5 The numbers shall be placed immediately above the graduation lines to which they refer, and slightly to the side of the adjacent shorter lines. 6.3 Nos.2 and2A hydrometer scales 6.3.1 All graduation lines shall extend completely round the circumference of the stem. 6.3.2 The numbers representing the nominal li
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