BS ISO 1656 pdf free download

BS ISO 1656-2019 pdf free download.Rubber, raw natural, and rubber latex, natural — Determination of nitrogen content.
4.1.1 Catalyst mixture or catalyst solution
CAUTION — When working with selenium, avoid breathing vapours and/or contact with skin or clothing. Work only with adequate ventilation.
4.1.1.1 Catalyst mixture
Prepare a finely divided intimate mixture of the following:
— 30 parts by mass of anhydrous potassium sulfate (K 2 SO 4 );
— four parts by mass of copper sulfate pentahydrate (CuSO 4 ·5H 2 O);
— one part by mass of selenium powder or two parts by mass of sodium selenate decahydrate (Na 2 SeO 4 ·10H 2 O).
4.1.1.2 Catalyst solution
Dissolve, with heating, the following:
— 110 g of anhydrous potassium sulfate;
— 14,7 g of copper sulfate pentahydrate;
— 3,7 g of selenium or 7,49 g of sodium selenate, in 600 cm 3 of sulfuric acid (4.1.2).
4.1.2 Sulfuric acid, ρ = 1,84 g/cm 3 .
4.1.3 Sulfuric acid standard volumetric solution, c(H 2 SO 4 ) = 0,05 mol/dm 3 .
4.1.4 Sodium hydroxide standard volumetric solution, c(NaOH) = 0,1 mol/dm 3 .
4.1.5 Sodium hydroxide solution, c(NaOH) approximately 10 mol/dm 3 .
Dissolve 400 g of solid sodium hydroxide in 600 cm 3 of water and dilute to 1 000 cm 3 .
4.1.6 Boric acid solution, c(H 3 BO 3 ) approximately 0,17 mol/dm 3 .
Dissolve 10,5 g of solid boric acid in water, warming if necessary, and dilute to 1 000 cm 3 then cool the solution to room temperature.
4.1.7 Mixed indicator solution.
Dissolve 0,1 g of methyl red and 0,05 g of methylene blue in 100 cm 3 of at least 95 % (V/V) ethanol.
This indicator might deteriorate during storage and shall therefore be freshly prepared.
4.2 Apparatus
Ordinary laboratory apparatus and Kjeldahl apparatus, with a digestion flask of capacity 800 cm 3 .
4.3 Sampling and preparation of test portion
For the determination of nitrogen in raw solid rubber, a test portion shall be taken from the homogenized piece, sampled and prepared in accordance with ISO 1795.
For the determination of nitrogen in latex, a representative portion (as specified in ISO 123) of thoroughly mixed latex containing about 2 g of total solids shall be dried to constant mass, as specified in ISO 124.BS ISO 1656 pdf download.