BS ISO 1656:2019 pdf free.Rubber; raw natural, and rubber latex, natural – Determination of nitrogen content.
A known mass of the sample is digested with a mixture of sulfuric acid and catalytic amount converting nitrogen compounds into ammonium hydrogen sulfate from which the ammonia is distilled after making the mixture alkaline. The distilled ammonia is absorbed either in standard volumetric sulfuric acid solution followed by titration of the excess acid with a standard volumetric base solution or in boric acid solution followed by titration with standard volumetric acid solution (as boric acid is a weak acid, it does not affect the indicator used for this titration].5.4.2 Carry out the absorption and titration of the liberated ammonia by the procedure described in a) or b]. The temperature of the receiving flask shall be maintained below 30。C to prevent any loss of ammonia. Ensure proper disposal of the selenium-containing waste in the distillation flask. a] Place 75 cm3 of water and, by means of a pipette, 25,0 cm3 of the standard volumetric sulfuric acid solution (5.1.4) in the receiving flask of the distillation unit together with two drops of mixed indicator solution (5.1.8]. Position the receiving flask so that the end of the delivery tube from the condenser dips below the surface of the absorbing solution. While holding the stopper of the digestion flask in place, thoroughly mix the contents by swirling. Immediately begin distillation and continue at a steady rate until 200 cm3 of distillate have been collected. If the colour of the indicator changes, it indicates alkalinity of the absorbing solution. Discontinue the determination and repeat the procedure using more sulfuric acid or a smaller test portion. When the distillation is complete (normally, when the volume in the flask reaches about 300 cm3), titrate the contents with the sodium hydroxide solution (5.1.5), reading the burette to the nearest 0,02 cm3. b] Place 100 cm3 of the boric acid solution (5.1.7) in the receiving flask of the distillation unit with two drops of the mixed indicator solution (5.1.8]. Carry out the distillation as described in a) and titrate the distillate with the sulfuric acid solution (5.1.4), reading the burette to the nearest 0,02 cm3.BS ISO 1656 pdf download.