Random Section of GOST 127.2-93
5.3 Weight method
5.3.1 Essence of the method
The method is based on determination of the residue by weight according to the mass difference after double baking of a sample at a temperature of (250±10)°С and (800±10)°С;
— electric laboratory resistance furnace of СНОЛ type which assures a stable heating temperature of (800±10)°С and (250+10)°С;
— desiccator 2-230 according to GOST 25336;
— bowl 50 according to GOST 19908;
— sand bath.
5.3.3 Procedure of the analysis
(50±1) g of a sample are placed in the bowl previously baked and weighed. The sample is melted and at baked on a sand bath. Then the bowl with residue is baked at a temperature of (250±10)°С during 2 hours to eliminate markings of sulphur.
The bowl with residue consisting of organic substances and ash is brought to the desiccator, is cooled and weighed. Then the bowl with residue is placed in the electric furnace, is baked at a temperature of (800±10)°С till obtaining of a stationary mass, is cooled in the desiccator and is weighed. The results of all weightings in terms of grams are written down accurate within the third decimal digit after the point.
5.3.4 Processing of the results
Organic substances weight fraction Х5, %, is calculated by the following formula:
where m — mass of the tested sample, g;
m1 — residue mass containing organic substances and ash, g;
m1 — residue mass after baking in electric furnace, g;
The arithmetic mean of the results of at least two replicated determinations, the relative discrepancy between which does not exceed the allowable discrepancy equal to 30 % of the mean value, is taken as results of the analysis.
The limits of an allowable total relative error of results of the analysis are ± 15 %.
5.4 Extinction method
5.4.1 Essence of the method
The method is based on extraction of organic substances by means of chloroform or carbon tetrachloride in the Sokslet apparatus and determination of the residue by weight after evaporation of dissolver. The method cannot be applied in case of presence of volatile organic substances soluble in water.
5.4.2 Equipment, reagents and solutions:
— nozzle НЭТ-100 ТС according to GOST 25336;
— desiccator of СНОЛ type which assures a stable heating temperature of (70±2)°С;
— water bath or single-burner electric range according to GOST 14919;
— beaker В-1-400 ТХС according to GOST 25336;
— cylinder 1-250 according to GOST 1770;
— desiccator 1-230 according to GOST 25336;
— water-jet pump according to GOST 25336;
— evaporating bowl 4 according to GOST 9147;
— laboratory filter paper according to GOST 12026;
— ethyl alcohol for technical use according to GOST 18300;
— chloroform or carbon tetrachloride according to GOST 20288, just-distilled;
— 9-aqueous sodium sulphide according to GOST 2053, solution with a weight fraction of 45 % (solution is to be transparent).