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Ref. No. : ISO/R 847-1968(E)
IS0
I NTERN AT1 ON A L O RG A N IZATl ON FOR STA N DA RDIZATION
IS0 RECOMMENDATION
R 847
PHOSPHORIC ACID FOR INDUSTRIAL USE
DETERMINATION OF SULPHATE CONTENT
Volumetric method
1st EDITION
October 1968
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belongs to IS0 Member Bodies. Reproduction of these
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by the national standards organization of that country, being
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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 847, Phosphoric acid for industrial use - Determination of
sulphate content - Volumetric method, was drawn up by Technical Committee ISO/TC 47, Chemistry,
the Secretariat of which is held by the Ente Nazionale Italian0 di Unificazione (UNI).
Work on this question by the Technical Committee began in 1960 and led, in 1966, to the
adoption of a Draft IS0 Recommendation.
In December 1966, this Draft IS0 Recommendation (No. 1108) 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 :
Israel Spain
Austria
Belgium Italy Switzerland
Brazil Japan Thailand
Bulgaria Korea, Dem. P.R. of Turkey
Chile Korea, Rep. of U.A.R.
Czechoslovakia New Zealand U.S.S.R.
Germany Poland Yugoslavia
Hungary Romania
India South Africa, Rep. of
Two Member Bodies opposed the approval of the Draft :
France
United Kingdom
Y
The Draft IS0 Recommendation was then submitted by correspondence to the IS0 Council,
which decided, in October 1968, to accept it as an IS0 RECOMMENDATION.
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lSO/R 847-1968(E
IS0 Recommendation R 847 October 1968
PHOSPHORIC ACID FOR INDUSTRIAL USE
DETERM NATION OF SULPHATE CONTENT
Volumetric method
1. SCOPE
This IS0 Recommendation describes a volumetric method for the determination of the sulphate
content in phosphoric acid for industrial use.
2. FIELD OF APPLICATION
The general method is applicable to the determination of the sulphate content in phosphoric acid for
industrial use greater than 0.30 (m/m) of H, SO, content.
2.1 Special case
Phosphoric acid for industrial use containing polyphosphoric acids (see section 8).
NOTE. - In case there is no certainty of absence of polyphosphoric acids, carry out the determination
according to the procedure of the special case directly.
3. PRiNCIPLE
Separation of SO,’ -ions as benzidine sulphate. Aikalimetric titration, in the presence of phenol-
phtalein, as indicator, of the sulphuric acid evolved by hydrolysis.
4. REAGENTS
Distilled water or water of equivalent purity should be used in the test.
4.1 Potassium carbonate, anhydrous.
4.2 Hydrochloric acid, approximately d = 1.19, 37 (m/m) or 12 N solution.
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ISO/R 847-19681E
4.3 Benzidine hydrochloride, 28 g/l solution.
Dissolve 28 g of benzidine hydrochloride in approximately 500 ml of warm water and then add
20 ml of the d = 1.19 hydrochloric acid solution. Cool, dilute to 1000 ml and filter if required.
Because of its carcinogenic nature, handle benzidine with care.
4.4 Sodium hydroxide, 0.1 N standard volumetric solution (see Note, section 7).
4.5 Phenolphthalein, 10 g/l ethanolic solution.
Dissolve 1 gofphenolphthaleinin95 (v/v),ethanoland dilute to 100 ml with the same ethanol.
4.6 Wash solution
Make a suspension of 0.5 g of carefully washed benzidine sulphate in one litre of water. Shake
mechanically for about 2 hours at room temperature and then filter.
5. APPARATUS
Ordinary laboratory apparatus.
6. PROCEDURE
6.1 Test portion
Weigh by difference, to the nearest 0.01 g, approximately 20 g of the test sample.
6.2 Preparation of sample solution
Place the test portion (6.1) in a beaker of suitable capacity (250 ml for example), add
approximately 1 g of potassium carbonate (4.1) and boil for about 20 minutes.
Cool and allow to stand, then fiter and wash the precipitate until it is acid-free, collecting
quantitatively filtrate and washings in a 200 ml one-mark volumetric flask. Add 10 ml of
hydrochloric acid solution (4.2), dilute to the
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