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Ref. No. : ISO/R 696-1968 (E)
IS0
I N TERN AT1 ON A L O RG A N IZ AT1 O N FO R STA N DA RD I2 AT1 ON
IS0 RECOMMENDATION
R 696
SURFACE ACTIVE AGENTS
MEASUREMENT OF FOAMING POWER
1st EDITION
March 1968
COPYRIGHT RESERVED
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
IS0 Recommendation R 696, Surface active agents - Measurement of foamingpower. was
The
drawn up by Technical Committee lSO/TC 9 I, Surface active agents, the Secretariat of which is held
by the Association Française de Normalisation (AFNOR).
Work on this question by the Technical Committee ISO/TC 91 began in 1960 and led. in 1965,
to the adoption of a Draft IS0 Kecomnicndation.
In May 1966. this Draft IS0 Recommendation (No. 985) 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 Romania
Austria Ireland South Africa, Rep. of
Belgium
Israel Spain
Brazil
Italy Sweden
Canada Japan
Switzerland
Chile Korea, Rep. of
Turkey
Czechoslovakia Netherlands 1J.A.R
France New Zealand United Kingdom
Germany Poland U.S.S.R.
Greece Portugal Yugoslavia
No Member Body opposed the approval of the Draft.
The Draft IS0 Recommendation was then submitted by correspondence to the IS0 Council
which decided, in March 1968, to accept it as an IS0 RECOMMENDATION.
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ISOlR 696 -1968 (E
March 1968
IS0 Recommendation R 696
SURFACE ACTIVE AGENTS
MEASUREMENT OF FOAMING POWER
1. SCOPE
This IS0 Recommendation describes a method of measurement of the foaming power of a surface
active agent.
2. FIELD OF APPLICATION
This method is applicable to all surface active agents. Measurement of the foaming power of solutions
of readily hydrolysable agents, however, does not give reliable results, as the hydrolysis products
collect in the films of liquid and affect the persistence of the foam.
NOTE. ~ The persistence of liquid films is very sensitive to the presence of particles of insoluble matter. This
method of measurement of foaming power should be used only with the greatest of care, therefore, for measuring
the foaming power of compositions based on surface active agents of which the solubility is rarely complete.
Foaming power is also very sensitive to small variations in composition. Consequently, the results obtained on
formulated products should be interpreted with caution.
This method is not applicable for measurement of the foaming power of very dilute solutions of surface active
agents, such as river waters containing surface active agents.
3. DEFINITIONS
3.1 Foaming power. Ability to produce foam.
NOTE. ~ In this IS0 Recommendation, foaming power is characterized by the volume of foam obtained
under specific experimental conditions. The decay of this volume of foam during the 5 minutes following its
formation is also relevant.
3.2 Foam. A mass of small gas cells, separated by thin fdms of liquid and formed by the juxtapo-
sition of bubbles, giving a gas dispersed in a liquid.
4. PRINCIPLE
Measurement of the volume of foam obtained after running 500 ml of a solution of a surface active
agent, from a height of 450 mm, on to a liquid surface of the same solution.
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ISO/R 696-1968 (
5. APPARATUS
5.1 Test apparatus
5.1.1 Components of apparatus (see Fig. 1 and 2)
5.1.1.1 Separating funnel of 1 litre capacity, consisting of a pear-shaped bulb to the upper end
of a tube about 200 mm long, having a tap at the lower end. The funnel carries a mark,
150 mm above the axis of the tap, which indicates the lower limit of discharge during
the test. The lower end of the tube is cut off strictly perpendicular to its length,
40 mm below the axis of the tap. The tap is moulded, not blown, the hole through the
key being of sufficient diameter (not less than 3 mm) to avoid undue obstruction of
the flow of the liquid.
5.1.1.2 Measuring cylinder of 1 litre capacity, complying with IS0 Recommendation R.*,
with graduations at each 10 ml. The measuring cylinder stands in a water-bath fitted
with a thermostat, the bath being sufficiently large to accommodate the measuring
cylinder immersed up to half its height.
5.1.1.3 Srand comprising a vertical rod, sufficiently long to allow the separating funnel and
the measuring cylinder to be held in place. To ensure that the assembly is centred and
so maintained during the measurement, the separating funnel is held by means of
two rings, one supporting the spherical part, the other of much smaller diameter
placed as low as possible around the stem of the separating funnel, below the tap. The
measuring cylinder is held in place by means of a screw-clamp with one movable jaw.
5.1.1.4 Stainless steelmetering tube, 70 mm long, 1.9 f 0.02 mm internal diameter and
0.3 mm wall thickness. The ends of the tube should be cut accurately at right angles
to the axis of the tube, in a precision tool lathe.
5 to 10 mm long, of internal
The metering tube is a push fit in a steel mounting tube
diameter equal to the external diameter of the metering tube, and of external diameter
equal to that of the lower end of the glass tube of the separating funnel. The upper
ends of the metering tube and of the mounting tube should be in the same plane. The
mounting tube is fixed by means of a short length of thick rubber tube (vacuum
tubing) so that the upper end of the mounting tube is in contact with the lower end of
the glass tube.
5.1.2 Cleaning of apparatus
Perfect cleanliness of the apparatus is essential for the success of the test
Before the test, and, if possible, overnight, leave all glassware in contact with chromic-
sulphuric acid mixture, prepared by slowly stirring concentrated sulphuric acid
(pz0 = 1.83 g/ml), into an equal volume of a saturated solution of potassium dichromate.
Rinse the apparatus first in distilled water until free from acid and then with a small
quantity of the solution under test.
Keep the mounting tube and metering tube assembly for 30 minutes in the vapour of an
azeotropic mixture of ethanol and trichlorethylene, then rinse it with a small quantity of
the solution under test.
Between ea
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