ISO INTERNATIONAL STANDARD 7537 Second edition 1997-07-15 Petroleum products -- Determination of acid number -- Semi-micro colour-indicator titration method Produits pétroliers - Determination de I'indice d'acide - Methode de titrage semi-microparindicateurcoloré ISO Reference number ISO 7537:1997(E) HS unde ermitted without license from IHS Not for Resale ISO 7537:1997(E) Foreword IsO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through IsO a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non- governmental, in liaison with iso, also take part in the work. .ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. International Standard ISO 7537 was prepared by Technical Committee ISO/TC 28, Petroleum products and lubricants. This second edition cancels and replaces the first edition (ISO 7537:1989), which has been technically revised. Annex A of this International Standard is for information only. ISO1997 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the publisher. InternationalOrganizationforStandardization Case postale 56 . CH-1211 Geneve 20 : Switzerland Internet [email protected] X.400 C=ch; a=400net; p=iso; o=isocs; S=central Printed in Switzerland atinalgazaiSandardizato license from IHS Not for Resale ISO 7537:1997(E) INTERNATIONALSTANDARD ISO Petroleum products - Determination of acid number - Semi-micro colour-indicator titration method WARNING -- The use of this International Standard may involve hazardous materials, operations and 1 Scope This International Standard specifies a semi-micro colour-indicator method for the determination of acidic constituentsinneworusedpetroleumproductsandlubricantssolubleinmixturesoftolueneandpropan-2-ol,or capable of existing as suspensions in such mixtures, and where the suspended material is sufficiently dissociated that its acidic components can be titrated. The method is especially intended for applications in which the amount of sample available to be analysed is too dissociation constants in water larger than 10-9. Extremely weak acids having dissociation constants smaller than 10-9 do not interfere. Salts titrate if their hydrolysis constants are larger than 10-9. conditions. Although the titration is made under definite equilibrium conditions, the method does not measure an absolute acidic property that can be used to predict performance of an oil under service conditions. No general relationship between bearing corrosion and acid number is known. b) allowing additional acid number analyses to be made while maintaining the same test sample depletion, and thus providing additionaldata NOTE 3 Some oils, such as many cutting oils, rustproofing oils, and similar compounded oils, or excessively dark-coloured oils, may be more difficult to analyse by this method due to obscurity of the colour-indicator end-point. These oils can be analyzed by Iso 6619 provided sufficient sample is available. However, this situation is much less likely using this International Standard than using iso 6618, since the sample is more dilute during the titration and the end-point colour change is more stable. The acid numbers obtained by this method may or may not be numerically the same as those obtained by Iso 6619, buttheyshouldbeofthe sameorderofmagnitude. NOTE 4 The results obt