IS0 57: 1975 pdf download – Bleached lac – Specification.
A.l PRINCIPLE A.l.l The volatile matter (moisture) content of bleached lac is determined in two stages, the first stage being by drying a weighed specimen of the “sample as received” marked “for the determination of volatile matter (moisture) content” by keeping it over concentrated sulphuric acid in vacuo for 12 to 24 h. In the case of bone-dry bleached lacs, this first stage may be omitted. A.1.2 For the second stage, the partially dried material thus obtained is ground to the specified size, and a portion is dried further by heating it in a well-ventilated oven maintained at a temperature of 41 f 2 OC for 18 h. A.2 PROCEDURE A.2.1 Use a portion of the “sample as received” (see 0.1.5, 0.1.6 and 0.1.7) and crush, if necessary, into granules using a heavy pestle and mortar, keeping the latter covered as far as possible during the process. Weigh a clean, dry, flat-bottomed dish of about 1 00 mm diameter, provided with a glass cover. Transfer approximately 10 g of the ground sample to the dish as rapidly as possible, cover it with the glass cover and reweigh. The difference gives the mass of test portion. A.2.2 Transfer the dish and contents to a vacuum desiccator containing concentrated sulphuric acid and remove the cover of the dish. Immediately evacuate the desiccator and keep the sample, uncovered, in vacuo for not less than 1 2 h and not more than 24 h. Remove the dish, replace the cover and weigh. The difference between this mass and the mass of the dish is the mass of the partially dried test portion. Grind it until it passes a sieve having a nominal aperture of 0,425 mm (see 0.4). A.2.3 Weigh approximately 5 g of the ground material, to an accuracy of 1 mg, into a covered tared dish of the type described in A.2.1 and transfer to a well-ventilated oven maintained at a temperature of 41 t 2 OC for 18 h, the cover of the dish being removed during the drying process. At the conclusion of the heating period, replace the cover and transfer the covered dish to a desiccator; weigh when cool. This mass minus the mass of the dish is the mass of the completely dried test portion.