1、BSI BSm4938 PART*:E! 8?2 W Lb24669 0159640 T W BS 4938 : Part 2 : 1982 UDC 637.12.068.07 O British Standards Institution. No part of this publication may be photocopied or otherwise reproduced without the prior permission in writing of BSI. British Standard O Dirt content of milk Part 2. Method for
2、the determination of visible dirt content (rapid method) Teneurs en impurets du lait Partie 2. Mthode de dtermination de la teneur en impurets visibles (mthode rapide) Verunreinigungen in Milch Teil 2. Verfahren zur Bestimmung des Gehalts an sichtbaren Fremdstoffen (Schnellverfahren) British Standar
3、ds Institution L- , I - ES1 BS*4938. PART*2 82 W 31624bb OL5b4L L BS 4938 : Part 2 : 1982 Contents Foreword Cooperating organizations Method O. Introduction 1. Scope 2. Definitions 3, Principle 4. Reagent 5. Apparatus 6. Preparation of test sample 7. Procedure 8. Expression of results 9. Test report
4、 Page Inside front cover Back cover Appendices A. Information on the relationship between results obtained by the reference method described in BS 4938 : Part 1 and the rapid method 1 1 1 1 1 1 2 2 2 2 3 Foreword This Part of BS 4938 has been prepared under the direction of the Dairying Standards Co
5、mmittee and together with Part 1 supersedes BS 4938 : 1973 which is withdrawn. The 1973 edition of this standard described a rapid routine method for determining sediment in milk by filtration. In reviewing that method it was decided that it should be replaced by a reference method and a rapid metho
6、d, published separately. Furthermore, it was agreed that what these methods determined would be more appropriately described as dirt and visible dirt rather than sediment. The rapid method determines visible dirt in milligrams per litre of milk (mg/L), by means of rapid filtration and the use of pho
7、tographic standard filter discs whereas in the reference method, centrifuging, and then chemical treat- ment of the deposit obtained, are employed to determine dirt (moist), in microlitres per litre of milk (pL/L). Page B. Information on the preparation of the C. Method for assessing the suitability
8、 of filter material 8 D. Bibliography 8 photographic standard filter discs 4 Table 1. Composition of coarse and fine dirt 4 Figures 1. Layout of a suitable filtration apparatus 5 2. Photographic standard filter discs showing mass, in milligrams, of visible dirt (fine) per litre of milk 6 3. Photogra
9、phic standard filter discs showing mass, in milligrams, of visible dirt (coarse) per litre of milk 7 The only major innovation in this revision of BS 4938 : 1973 is the augmentation of the original set of photo- graphic standard filter discs depicting six levels of standard dirt with a set of six st
10、andard discs depicting fine dirt, at the same levels. This was done to make it easier to assign a dirt level to a wet filter disc containing dirt, when comparing the appearance of the disc with the photographic standards, now that with the increasing use of in-line milk filters the size of dirt part
11、icles found in milk is decreasing. However, for convenience, the two sets of photographic standards discs relate to fine dirt and coarse dirt respectively, the latter being exactly the same as the former standard dirt photographic standards. The photographic standard discs are also available separat
12、ely as BS 4938 : Part 2P. Compliance with a British Standard does not of itself confer immunity from legal obligations. BSI BSX493B PART*Z 82 Lb211bb 03596112 3 BS 4938 : Part 2 : 1982 British Standard Dirt content of milk Part 2. Method for the determination of visible dirt content (rapid method) O
13、. Introduction The rapid method described in this Part is intended to be of the most general application, suitable for use in field conditions as well as in the laboratory, and therefore every effort has been made to keep the apparatus and procedure as simple as is consistent with the accuracy requi
14、red. To this end, specification of the apparatus has been confined to essentials and does not exclude the possibility of modifying existing apparatus that is commercially available. 0 1. Scope This Part of BS 4938 describes a rapid method for the determination of the visible dirt content of milk. Th
15、e method is primarily intended for application to raw herd milk and raw bulk milk but it can be applied to any milk (whole, partly skimmed or skimmed), raw or heat treated, except milk that does not filter readily because of abnormalities which would in any case render it unaccept- able. Appendix A
16、gives information on the relationship between results obtained by the reference method (see BS 4938 : Part 1) and the rapid method. Appendix B gives information on the preparation of the photographic standard filter discs. Two sets of photographic standard filter discs are included: these illustrate
17、 the appearance of discs through which milks with six levels of fine dirt and coarse dirt respectively have been filtered. Appendix C described a method for assessing the suitability of materials for use as filter discs. A bibliography is given in appendix D. NOTE. The titles of the publications ref
18、erred to in this standard are listed on the inside back cover. 2. Definitions For the purposes of this Part of BS 4938, the following definitions apply. 2.1 visible dirt. Any insoluble material, e.g. vegetable matter from dung, feed or bedding and inorganic matter from coil or dust, that has entered
19、 milk after the milk has left the udder and which is visible when retained on the specified filter disc. 2.2 visible dirt content. Milligrams of dirt (fine or coarse) per litre of milk (.e. mg/L). 3. Principle A test portion at a temperature of 20C to 25C (or at 35 “C to 40 OC if necessary) is filte
20、red within three minutes through a filter disc. The visible dirt retained on the disc is 0 expressed as the content of visible dirt (fine or coarse) of the laboratory sample by visual comparison with photo- graphic standard filter discs. 4. Reagent 4.1 Water, such that when 200 mL are filtered as de
21、scribed for milk in clause 7, the filter disc remains perfectly clean. 5. Apparatus 5.1 Thermometer, complying with BS 1704, covering the range -5 “C to +I05 “C and graduated in 1 OC divisions. 5.2 Water bath, capable of adjusting the temperature of the laboratory sample to between 20 “C and 25 “C o
22、r 35 OC and 40 OC. 5.3 Graduated measuring cylinder, plastics, of capacity 250 mL. NOTE. A plastics rather than a glass cylinder is more appropriate for field conditions and the lower heat capacity of the former minimizes any decrease in milk temperature during 7.2. 5.4 filtration apparatus (see fig
23、ure 1) having the following features: (a) an area of filtration defined by an orifice of internal diameter 10 f 0.2 mm, which may be achieved, where necessary, by a gasket situated over the filter disc; (b) means for facilitating the passage of milk through the filter disc by application of pressure
24、 or vacuum in a way which does not cause the flow of milk to distort the threads of the filter disc; (c) ancillary equipment, such as a hand/foot pressure pump or a suction pump, to complete the filtration of 200 mL of milk in as short a time as possible, and in any case within 3 min, but giving a d
25、ifferential pressure not greater than 100 kPa; (d) a means, such as the incorporation of a safety device, to ensure that the maximum differential pressure specified in (c) cannot be exceeded. NOTE. Filtration apparatus complying with the above requirements is commercially available or can be constru
26、cted by suitable modifi- cation of similar commercially available filtration apparatus. 5.5 Filter disc, complying with C.6, approximately 32 mm in diameter, made of natural and/or synthetic fibre and white in colour. NOTE. Filter discs made of Absorbent Lint (BPC) or the filtering material known as
27、 Lintine have been found to be suitable. 5.6 Wash bottle, of capacity 500 mL. 1 - BSI BS#q38 PART*2 82 R lb24bb Ol5b43 5 m BS 4938 : Part 2 : 1982 6. Preparation of test sample Take a laboratory sample of sufficient volume to provide a test portion of 200 mL. NOTE I. General guidance on the sampling
28、 of milk is given in 6.5 809. This guidance has been shown to be satisfactory when taking milk samples, for determination of dirt content, from road tankers (Harding (b) the visible dirt content (see clause 8) and the date determined; (c) any information indicating that the result obtained in (b) ma
29、y be unreliable, or any exceptional features observed during the procedure; (d) reference to this standard (.e. BS 4938 : Part 2). O O O O t BSI BSX11938 PART*Z 82 = LbZLibb OL59b114 7 = BS 4938 : Part 2 : 1982 Appendix A Information on the relationship between results obtained by the reference meth
30、od described in BS 4938 : Part 1 and the rapid method A.l General. In appendix A of BS 4938 : Part 1 : 1982 it is suggested that a dirt content of 30 pL/L or more, obtained by the reference method described in Part 1, should be regarded as unacceptable. Since the rapid method described in this Part
31、may also be used to assess whether the visible dirt content of a milk is acceptable or not, it is necessary to find what visible dirt content obtained by the rapid method in mg/L is equivalent to 30 pL/L or more. This appendix examines the evidence available on this question. A.2 Comparison of resul
32、ts. There has been as yet no direct comparison of results obtained on the same samples of milk by the two methods but some information is available on the relationship of results obtained by the earlier similar methods described by Millard fine sand was difficult to prepare and con- sequently was om
33、itted in the preparation of fine dirt. The dung ( 180 pm) and the earth ( 425 vm) were each suspended in water and filtered through a commercial in-line milk filter of 98 pm aperture size. The fine particles ( 98 pm) of dung and earth in the filtrates were recovered and dried, a dry-matter determina
34、tion was performed on each, and then the two preparations were mixed as shown in table 1 in the ratio 80:20 (dung to earth) to obtain fine B.3 Preparation of filter discs with deposits of fine dirt and coarse dirt. Fresh milk was filtered through a milk strainer, using a good quality filter pad, and
35、 O, 0.5, 1.0, 2.0, 3.0 and 5.0 mg of fine dirt (see B.2) were added to 1 L samples of the filtered milk. The same masses of coarse dirt (see B.2) were added to another set of 1 L samples of the filtered milk. After stirring the milk samples, 200 mL of each were filtered in accordance with clause 7,
36、using Lintine filter discs complying with appendix C. The filter discs thus prepared were photographed while still wet to obtain the photographic standard filter discs shown in figures 2 and 3. Table 1. Composition of coarse and fine dirt Material (dried) Dung Earth Sand Total Passes through apertur
37、e size vm (see note) 850 425 180 - 850 425 425 - I vm 850 425 180 I 850 425 - I % (mim) 12.0 28.6 1 28.6 10.7 6.0 2.6 7.5 I ”- 100.0 y basis) Fine dirt - - 20.0 100.0 dirt, The ratio Of dung to earth in the fine dirt was similar to that in the coarse dirt. NOTE. Pieces of fibre longer than 5 mm were
38、 excluded from the dried dung used. 4 Gasket View on A-A Filter disc View on B-B ES1 BS*4738 PART*2 2 = Lb2Libb7 OLSb4b O BS 4938 Y Part 2 : 1982 Pressure - 17E 000000000 0000000000 00000000000 o 000000000 000000000 Support disc View on C-C Suction Carrier View on A-A Ail dimensions are in millimetr
39、es. Figure 1. Layout of a suitable filtration apparatus 5 BSI BS*1143B PART*2 82 W Lb211hb7 OL596117 2 W BS 4938 : Part 2 : 1982 NOTE, Actual size Figure 2. Photographic standard filter discs showing mass, in milligrams, of visible dirt (fine) per litre of milk 6 0.0 mg/L 0.5 mg/L 1 .O mg/L BSI BS*1
40、(938 PART*2 82 162L1bh OL57h48 L1 BS 4938 1 : Part 2 : 1982 NOTE. Actual size 5.0 mg/L 3.0 mg/L 2.0 mg/L Figure 3. Photographic standard filter discs showing mass, in milligrams, of visible dirt (coarse) per litre of milk 7 ES1 BS*4938 PARTx2 82 W 3624bb9 0359649 b BS 4938 : Part 2 : 1982 Appendix C
41、 Method for assessing the suitability of filter material C.1 Principle. A suitable filter permits the passage of milk constituents through the material, but retains extraneous matter as a deposit on the surface of the filter. The suit- ability of a filter material is assessed by determining the quan
42、tities of particles of known size that will either pass through or be retained by the filter. Although the largest particles in normal milk are fat globules which rarely exceed 20 pm in diameter, it has been found necessary to permit passage of particles up to about 50 pm to obtain suitable filterin
43、g characteristics. C.2 Reagents C.2.1 Natural quartz particles* (reference material) graded as follows: coarse grade, 12 to 90 pm (ref. no. CRM-RM no. 69) fine grade, 3 to 20 pm (ref. no. CRM-RM no. 67) C.2.2 Water, complying with 4.1. (2.3 Apparatus C.3.1 Glass beakers, heat resistant, squat form w
44、ith spout, of capacity 150 mL and with a graduation mark at 100 mL. C.3.2 Glass stirring rods. (2.3.3 Filtration apparatus, complying with 5.4. C.3.4 Drying oven, complying with BS 2648, capable of operating at 102 f 1 .O OC throughout the working space. C.3.5 Desiccator. C.3.6 Glass centrifuge bott
45、les, of capacity 250 mL. 2.3.7 Centrifuge, with speed indicator (r/min), having vertical loading swing-out cups to accommodate the centrifuge bottles (C.3.6), capable of producing an accelera- tion of 900 f. 50gn at the internal bottom of the bottles while maintaining a temperature of between 20 OC
46、and 25 “C within the centrifuge, and complying with BS 4402. NOTE. The acceleration,gn, produced in a centrifuge is given by the expression where . gn = 1.12 RN2 X R is the effective horizontal radius (in mm); N is the speed (in rlmin). C.3.8 Suction device, consisting of a glass tu be of 4 mm inter
47、nal diameter (with the bottom end upturned by 10 mm) connected to a water pump. C.3.9 Balance, capable of weighing to 0.1 mg. C.4 Procedure C.4.1 Preparation of suspensions of fine and coarse particles. Weigh into separate beakers (C.3.1) to the nearest 0.1 mg about 50 mg to 60 mg of coarse and fine
48、 quartz particles (C.2.1). Make each up to 100 mL with water and stir well with a glass rod. NOTE 1. It is important that the particles are dispersed thoroughly before transfer of the suspension to the filtration apparatus is made to avoid preliminary blockage on the filter disc by gravitational set
49、tlement. NOTE 2. The reference quartz particles are non-deliquescent and supplied in air-tightcontainers; it is therefore not necessary to correct sample weights for moisture content. C.4.2 Retention of coarseparticles. Place the filter disc in oven (C.3.4) and dry for 1 h. Remove, disiccate, cool and weigh to the nearest 0.1 mg. Assemble the filtration apparatus (C.3.3) with the filter disc inserted (see 7.1). Pour the prepared suspension containing coarse grade particles into the apparatus and immediately carry out the filtration in accordance wit
