10 Expression of results
10.1 Method of calculation
The interfacial tension, δ, expressed in millinewtons per metre (mN/m), is given by the formula
δ = M x F
where
M is the calibrated scale reading of the tensiometer;
F is a factor calculated as follows:
where
δ0 is the density of water, in grams per millilitre, at 25 °C;
δ1 is the density of the test portion, in grams per millilitre, at 25 °C;
P is a constant calculated as follows:
where
rw is the radius, in millimetres, of the wire of the ring,
rr is the mean radius, in millimetres, of the ring.
10.2 Precision
The precision of the method, as obtained by statistical examination of inter-laboratory test results, is as follows:
10.2.1 Repeatability
The difference between successive test results, obtained by the same operator with the same apparatus under constant operating conditions on identical test material, would in the long run, in the normal and correct operation of the test method, exceed 2 % of the mean in only one case in 20.
10.2.2 Reproducibility
The difference between two single and independent results, obtained by different operators working in different laboratories on identical test material, would in the long run, in the normal and correct operation of the test method, exceed 5 % of the mean in only one case in 20.
11 Test report
The test report shall contain at least the following information:
a) the type and identification of the product tested;
b) a reference to this International Standard or to a national standard;
c) the result of the test (see 10.1);
d) any deviation, by agreement or otherwise, from the procedure specified;
e) the date of the test.