# The Milk (Special Designations) (Scotland) Order 1988, Paragraph 3: Reagents


(1) Reagents of analytical quality shall be used.
(2) The buffer-substrate solution shall be prepared as follows:—
(a) buffer solution: 3.5 g. of anhydrous sodium carbonate and 1.5 g.of sodium bicarbonate shall be dissolved in distilled water, and made up to one litre;
(b) substrate: Disodium p-nitrophenyl phosphate. The solid substrate shall be kept in a refrigerator;
(c) buffer-substrate solution: 0.15 g. of the substrate shall be placed in a 100 ml. measuring cylinder or graduated flask, and made up to 100 ml. with the buffer solution. The solution shall be stored in a refrigerator and protected from light. It shall give a reading of less than the standard marked 10 on the comparator disc A.P.T.W. or A.P.T.W.7 when viewed in transmitted light through a 25 mm. cell in the “all purposes” comparator, distilled water being used for comparison. The solution shall not be used for more than one week.

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Source: https://www.legislation.gov.uk/uksi/1988/2191/schedule/6/part/III/paragraph/3 (the official version)
Page: https://openlegislation.uk/milk-special-designations-scotland-order-1988/schedule-6/part-III/paragraph-3
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.