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IS0
IZ AT1 O N
I NT ERN AT1 O NA L O RG A N 17AT I ON FOR STAN DARD
I SO R E CO M M E N DATI O N
R 456
ANALYSIS OF SOAP
DETERMINATION OF FREE CAUSTIC ALKALI
1st EDITION
November 1965
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For each individual country the only valid standard is the national standard of that country.
Printed in Switzerland
Also issued in French and Russian. Copies to be obtained through the national standards organizations.
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BRIEF HISTORY
The IS0 Recommendation R 456, Analysis of Soap. Determination of Free Caustic
Alkali, was drawn up by Technical Committee ISO/TC 91, Surface Active Agents, the
Secretariat of which is held by the Association Française de Normalisation (AFNOR).
Work on this question by the Technical Committee began in 1961 and led, in 1962,
to the adoption of a Draft IS0 Recommendation.
In June 1963, this Draft IS0 Recommendation (No. 584) was circulated to all the
IS0 Member Bodies for enquiry. It was approved, subject to a few mod3cations of an
editorial nature, by the following Member Bodies :
Argentina
Hungary Poland
Austria Italy Portugal
Canada Japan Romania
Chile Korea, Rep. of Spain
Colombia Morocco Switzerland
Czechoslovakia
Net herlands United Kingdom
France New Zealand Yugoslavia
Germany Norway
One Member Body opposed the approval of the Draft: India.
The Draft IS0 Recommendation was then submitted by correspondence to the IS0
Council, which decided, in November 1965, to accept it as an IS0 RECOMMENDATION.
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iSO/ R 456 - 1965 (E)
I IS0 Recommendation R 456 November 1965
ANALYSIS OF SOAP
DETERMINATION OF FREE CAUSTIC ALKALI
INTRODUCTION
As soaps usually contain a small amount of unsaponified neutral fat, there is no perfect procedure
for determining free caustic alkali because, when the sample of soap is dissolved, a neutral fat is
more or less saponified by any free caustic alkali that is present.
Both methods described in this IS0 Recommendation are therefore of a conventional nature.
Conventionally, free caustic alkali is expressed as
sodium hydroxide (NaOH) for sodium soaps and
potassium hydroxide (KOH) for potassium soaps.
1. SCOPE
The purpose of this IS0 Recommendation is to specify two methods of determining free caustic
alkali in commercial soaps, excluding compounded products :
Method A, ethanol method,
Method B, barium chloride method.
1.1 Choice of method
Method A (ethanol method) should be applied only to sodium soaps of ordinary quality, as
the presence of certain additives brings in sources of error. It is not applicable to potassium
soaps, because of the solubility of potassium carbonate in ethanol.
Method B (barium chloride method) should be applied to all soft potassium soaps or mixed
sodium and potassium soaps. The application of this method to sodium soaps of ordinary
quality, which usually do not contain sufficient quantities of free caustic alkali to be deter-
mined by this method, is not recommended.
2. TERMINOLOGY
It is understood that free caustic alkali in a soft soap is the quantity of hydroxyl ion, reported as
potassium hydroxide (KOH), which is found in solution after precipitation with barium chloride
under the operating conditions described.
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IS0 R 456 - 1965 (E)
3. METHOD A
(Ethanol method)
3.1 Principle
The soap is dissolved in neutralized ethanol, and the free caustic alkali is titrated with an
ethanolic solution of hydrochloric acid.
3.2 Reagents
3.2.1 Ethanol, absolute.
3.2.2 Potassium hydroxide, ethanolic solution, approximately O. 1 N.
3.2.3 Hydrochloric acid, ethanolic solution, approximately O. 1 N.
3.2.4 Phenolphthalein solution, 1 g in 100 ml of 95 per cent by volume ethanol.
3.3 Apparatus
Ordinary laboratory apparatus, and in particular
(a) Flask of approximately 400 ml capacity, that can be fitted to a reflux condenser ;
(b) Reflux condenser ;
(c) Analytical balance.
3.4 Procedure
3.4.1 Test portion. Weigh approximately 5 g of soap to an accuracy of 0.01 g.
3.4.2 Determin
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