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UDC 661.185
IS0
STAN DARD I Z AT I O N
O RG A N I ZAT I O N FOR
I NT ERN AT1 O NA L
I S O R E CO M M E N DATI O N
R 455
ANALYSIS OF SOAP
DETERMINATION OF TOTAL CRUDE FATTY ACIDS
1st EDITION
November 1965
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The copyright of IS0 Recommendations and IS0 Standards
belongs to IS0 Member Bodies. Reproduction of these
documents, in any country, may be authorized therefore only
by the national standards organization of that country, being
a member of ISO.
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 455, Analysis of Soap. Determination of Total Crude
Fatty Acids, 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. 583) was circulated to all the
IS0 Member Bodies for enquiry. It was approved, subject to a few modifications of an
editorial nature, by the following Member Bodies :
Argentina Hungary Poland
Austria Italy Portugal
Canada Japan Romania
Korea, Rep. of Spain
Chile
Co 1 om b i a Morocco Switzerland
Czechoslovakia Netherlands 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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IS0 / R 455 - 1985 (E)
IS0 Recommendation R 455 November 1965
ANALYSIS OF SOAP
DETERMINATION OF TOTAL CRUDE FATTY ACIDS
1. SCOPE
The purpose of this IS0 Recommendation is to specify the method of determining total crude
fatty acids in commercial soaps, excluding compounded products.
In the Annex, there is also described a method which should be used only for routine controls
and for soaps in which the fatty acids are not contaminated with substances insoluble in water,
derived from additives (silicates etc.).
2. TERMINOLOGY
Total crude fatty acids means the water-insoluble fatty material which is collected by decom-
posing the soap with a strong mineral acid under the operating conditions described. This term
includes unsaponifiable matter, glycerides and any resinic acids contained in the soap, in addition
to the so-called fatty acids.
3. PRINCIPLE
The fatty acids are extracted with diethyl ether and titrated with a solution of sodium hydroxide
in ethanol.
4. REAGENTS
4.1 Diethyl ether, pure.
4.2 Ethanol solution, 95 % by volume.
4.3 Acid solution:
either sulphuric acid, d = 1.83, diluted 1/5 ; *
or hydrochloric acid, d = 1.19, diluted 113. *
4.4 Sodium chloride solution, 10 g of sodium chloride dissolved in 100 ml of distilled water.
4.5 Sodium hydroxide ethanolic solution, analytical grade, recently standardized to approxi-
mately 0.5 N.
Methyl-orange solution, 0.2 g in 100 ml of distilled water.
4.6
4.7 Phenolphthalein solution, 1 g in 100 mi of the ethanol solution (4.2).
* Diluted pJp. means that pi parts by volume of the specified solution are diluted to give p, parts by volume of the
final mixture.
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IS0 / R 455 - 1965 (E)
5. APPARATUS
Ordinary laboratory equipment and in particular,
(a) Porcelain or glass basins of about 250 ml.
(b) Separating funnels, of about 500 ml.
(c) Water-bath.
(d) Oven regulated at 120°C.
(e) Desiccator.
(f) Analytical balance.
6. PROCEDURE
6.1 Test portion
Weigh 5 to 10 g of soap into the basin to an accuracy of 0.001 g.
6.2 Determination
Make a hot solution in 100 ml of distilled water. Pour this aqueous solution into a separating
funnel, rinsing the basin with small quantities of distilled water.
Add a few drops of the methyl-orange (4.6) and then about 10 ml of the acid solution (4.3).
The indicator should turn red. If it does not, add 2 ml more of the acid solution (4.3). Leave
to cool to room temperature.
Add 100 ml of the diethyl ether (4.1). Shake the mixture vigorously for 1 min and allow to
stand until the two phases are completely separated.
Draw off the acidified water into a second separating funnel. Make a second extract of this
acid solution, mixing in the same way, with 50 ml of the diethyl ether (4.1).
Draw off the acidified water. Combine the ethereal solutions in the same separating funnel.
Wash twice in succession, using 50 ml of the sodium chloride solution (4.4) each time (mixing
for 1 min each time). Verify that the last wash is neutral to methyl-orange (4.6). If it is not,
continue washing in the same way until the washing solution is neutral to methyl-orange (4.6).
After drawing off the last washing solution, filter the ethereal solution, if necessary, through
a filter paper. Collect in a tared flask. Wash the filter with small portions of the diethyl ether
(4.1). Distil off nearly all the diethyl ether by boiling gently.
Dissolve the residue in 20 ml of the ethanol solution (4.2). Neutralize the ethanolic solution
of fatty acids with the ethanolic sodium hydroxide solution (4.5),* using 2 to 3 drops of
phenolphthalein (4.7) as indicator. Note the volume used.**
Remove the ethanol by placing on a boiling water-bath. Heat the flask in the oven at 120°C
until constant
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