GOST 11739.21-90

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  ГОСТ 11739.21-90

GOST 11739.21−90 Alloys aluminium cast and wrought. Methods for determination of chromium

GOST 11739.21−90

Group B59

STATE STANDARD OF THE USSR

ALLOYS ALUMINIUM CAST AND WROUGHT

Methods for determination of chromium

Aluminium casting and wrought alloys. Methods for determination of chromium

AXTU 1709

Valid from 01.07.91
before 01.07.96*
_______________________________
* Expiration removed
Protocol 5−94 N Interstate Council
for standardization, Metrology and certification
(IUS N 11/12, 1994). — Note the manufacturer’s database.

INFORMATION DATA

1. DEVELOPED AND INTRODUCED by the Ministry of aviation industry of the USSR

DEVELOPERS

V. G. Davydov, doctor of engineering. Sciences; V. A. Moshkin, PhD. tech. Sciences; V. I. Klitina, PhD. chem. Sciences; G. I. Friedman, PhD. tech. Sciences; M. N. Gorlova, PhD. chem. Sciences; O. L. Sikorska, PhD. chem. Sciences; L. N. Viksne

2. APPROVED AND put INTO EFFECT by Decision of the USSR State Committee on management of quality and standards from 28.06.90 N 1962

3. The frequency of inspection — 5 years

4. Standard corresponds to ISO 3978 in part wrought aluminium alloys, the essence of the method, measuring the optical density of the solution and results processing; ISO 4193 in part wrought aluminium alloys, essence method dissolve the sample, measurement of atomic absorption and processing of the results

5. REPLACE GOST 11739.21−78

6. REFERENCE NORMATIVE AND TECHNICAL DOCUMENTS

This standard establishes titrimetric (mass fraction of chromium with 0.1 to 1.0%), photometric (mass fraction of chromium in respectively from 0.05 to 1.0% and from 0.001 to 0.15%), atomic absorption (at a mass fraction of chromium from 0.01 to 1.0%) methods for determination of chromium.

1. GENERAL REQUIREMENTS

1.1. General requirements for methods of analysis GOST 25086 with the Supplement.

1.1.1. The result of the analysis taking the arithmetic mean of the results of the two definitions.

2. TITRIMETRICALLY METHOD FOR THE DETERMINATION OF CHROMIUM

2.1. The essence of the method

The method is based on dissolving the sample in a mixture of sulfuric and nitric, or a mixture of phosphoric, nitric and sulphuric acids, the oxidation of chromium to hexavalent neccersarily ammonium in the presence of a catalyst of silver nitrate and the titration of chromic acid solution of sulphate ferrous iron in the presence phenylanthranilic acid or diphenylamine as indicator.

2.2. Apparatus, reagents and solutions

Drying oven with thermostat.

Sulfuric acid according to GOST 4204, density 1.84 g/cmand раствор1:1.

Nitric acid according to GOST 4461, density 1,35−1,40 g/cm.

Orthophosphoric acid according to GOST 6552, a density of 1.70 g/cm.

Acids mixture: to 100 cmof water is poured 200 cmof sulphuric acid and after cooling 200 cmof nitric acid, the mixture is gently stirred.

Acids mixture B: 500 cmof phosphoric acid is mixed with 400 cmof nitrogen and 100 cmof sulphuric acid.

Manganese sulfate 5-water according to GOST 435.

Silver nitrate according to GOST 1277, a solution of 1 g/DM.

Ammonium neccersarily according to GOST 20478, a solution of 250 g/DM.

Sodium chloride according to GOST 4233, solution 100 g/DM.

Potassium dichromate according to GOST 4220, solution with molar concentration of 0.025 mol/DM(0,007355 g/cm — ): 7,3548 g recrystallized potassium dichromate is placed in a measuring flask with volume capacity of 1000 cm, dissolved in water, made up to the mark with water and mix the solution.

For recrystallization 100 g of potassium dichromate dissolved in 150 cmof water when heated to the boiling point of the solution. Vigorously stirring, the solution was poured in a thin stream in a porcelain Cup to obtain small crystals. The solution was cooled with ice water and precipitated crystals are filtered off with suction on a funnel with a porous glass plate, dried for 2−3 h at temperature (102±2) °C, crushed, and finally dried at a temperature of (200±5) °C for 10−12 h

Salt of protoxide of iron and ammonium double sulfate (salt Mora) according to GOST 4208, solution with molar concentration of 0.1 mol/DM: 40 g of salt Mora is placed in a beaker with a capacity of 800 cmand dissolved in 500 cmof water, poured 100 cmof sulfuric acid solution, cooled, transferred into a measuring flask with volume capacity of 1000 cm, made up to the mark with water and mix the solution.

To establish the mass concentration of salt Mora at the chromium () to two conical flasks with a capacity of 250 cmis placed 10 cmsolution of potassium dichromate and diluted to 150 cmof water, add 10 cmsulphuric acid of 3 cmof phosphoric acid, mix, add six drops phenylanthranilic acid or five drops of diphenylamine and titrated with a solution of salt Mora before moving crimson color of the solution in green or purple green.

Mass concentration of salt Mora in chrome (), g/cm, is calculated by the formula

, (1)

where is the mass concentration of the solution of potassium dichromate, g/cm;

 — the volume of potassium dichromate solution taken for titration, cm;

 — the volume of salt solution Mora, used for titration of potassium dichromate, cm;

0,3535 — the ratio of the mass of potassium dichromate on the weight of chromium.

Sodium carbonate according to GOST 83.

Acid N-phenylanthranilic on the other 6−09−3501, a solution of 2 g/DM: 0.2 g phenylanthranilic acid and 0.2 g of sodium carbonate dissolved in 50 cmof water, transfer the solution into a measuring flask with a capacity of 100 cm, made up to the mark with water and mix.

Diphenylamine according to GOST 5825, a solution of 5 g/lin concentrated sulfuric acidic

OTE.

2.3. Analysis

2.3.1. A portion of the sample weighing 2 g was placed in a conical flask with a capacity of 500 cm, 50 cm, pour themixture of acids and dissolved under moderate heating. In the analysis of alloys containing more than 1% silicon, the sample is dissolved in 50 cmof the mixture of acids B.

After dissolution, the sample flow 200 cmof hot water, dissolve the salt and cool the solution. Then pour 10 cmof a solution of silver nitrate and 25 cmof a solution of ammonium naternicola, the contents of the flask are heated to boiling and boiled until the appearance of crimson colour indicating complete oxidation of chromium. In that case, if the analyzed alloy contains manganese, after the dissolution of salts in the solution is added a crystal of sulphate of manganese. The solution continue to boil until the termination of allocation of small bubbles. Then add 5 cmof sodium chloride solution and boil the solution until the disappearance of the crimson color.

The cooled solution is titrated with a solution of salt Mora in the presence of 5−6 drops phenylantranilic acid until the solution colour from crimson to green, or in the presence of 4−5 drops of diphenylamine to change the color of the solution from purple to green

.

2.4. Processing of the results

2.4.1. Mass fraction of chromium () in percent is calculated by the formula

, (2)

where is the established mass concentration of salt solution Mora on the chrome (titer), g/cm;

 — the volume of salt solution Mora, used for titration of chromium, cm;

 — the weight of the portion of the sample,

2.4.2. Discrepancies in the results must not exceed the values given in table.1.

Table 1

3. The PHOTOMETRIC METHOD for the DETERMINATION of CHROMIUM (from 0.05 to 1.00%)

3.1. The essence of the method

The method is based on dissolving the sample in a mixture of phosphoric, sulfuric and nitric acids, formation after oxidation of the chromium to hexavalent neccersarily ammonium pink complex with diphenylcarbazide and subsequent measurement of optical density at a wavelength of 546 nm.

3.2. Apparatus, reagents and solutions

Spectrophotometer or photoelectrocolorimeter.

Orthophosphoric acid according to GOST 6552, a density of 1.70 g/cm.

Sulfuric acid according to GOST 4204, density 1.84 g/cmand a solution of 1:1.

Nitric acid according to GOST 4461, density 1,35−1,40 g/cm.

A mixture of acids, consisting of 550 cmwater 40 cmof sulphuric acid, 40 cmof phosphoric acid and 50 cmof nitric acid.

Hydrofluoric acid according to GOST 10484.

Silver nitrate according to GOST 1277, a solution of 4 g/DM.

Ammonium neccersarily according to GOST 20478, a solution of 8 g/DM.

The technical rectified ethyl alcohol according to GOST 18300.

1,5-Diphenylcarbazide on the other 6−09−07−1672, a freshly prepared alcoholic solution of 1.5 g/DM: 0.15 g difenilcarbazida placed in a volumetric flask with a capacity of 100 cm, add 15 cmof ethyl alcohol and heated the flask in hot water, leave for 15 minutes, then top up with water to the mark and mix.

Aluminium GOST 11069* brand А999.
_______________
* On the territory of the Russian GOST 11069−2001, here and hereafter. — Note the manufacturer’s database.

Chrome metal according to GOST 5905* brand H99.
_______________
* On the territory of the Russian Federation GOST 5905−2004, here and hereafter. — Note the manufacturer’s database.

Standard solutions of chromium.

Solution a: 0.5 g of chromium metal is placed in a conical flask with a capacity of 250 cmand dissolved by heating to 60 cmof sulfuric acid solution and transfer the solution into volumetric flask with a capacity of 500 cm, made up to the mark with water and mix.

1 cmof the solution contains 0.001 g of chromium.

Solution B: 10 cmsolution And placed in a volumetric flask with a capacity of 100 cm, made up to the mark with water and mix.

1 cmof solution B contains 0,

0001 g chromium.

3.3. Analysis

3.3.1. A portion of sample weighing 0.1 g was placed in a conical flask with a capacity of 100 cmand dissolved in 25 cmof a mixture of acids. Upon completion of the dissolution of the sample add 20−25 cmof water and filter the solution if it is not transparent, in a conical flask with a capacity of 250 cmthrough the filter medium density («white ribbon»). Filter the precipitate was washed 2−3 times with small portions of hot water and drop, if the mass fraction of silicon in the analyzed alloy does not exceed 1%.

3.3.2. When the mass fraction of silicon in excess of 1% of the filter with the sediment was placed in a platinum crucible, dried, incinerated, preventing ignition, and calcined at 500−600 °C for 2−3 min. After cooling in the crucible add four drops of sulphuric acid, 5 cmhydrofluoric acid and nitric acid drop by drop until a clear solution. The solution was evaporated to dryness and poured to the dry residue in the pot 2−3 cmof water and 2−3 cmof sulfuric acid solution. If necessary, the solution was filtered through a small tight filter («blue ribbon») and added to the main filtrate in the conical flask.

3.3.3. To the filtrate add 5 cmof a solution of silver nitrate, 5 cmnaternicola solution of ammonia, heat the solution and boil for 1 min. the Cooled solution was transferred to volumetric flask with a capacity of 100 cm, made up to the mark with water and mix.

3.3.4. Aliquot part of the solution 10 cmis placed in a volumetric flask with a capacity of 100 cm, top up with water up to 50−60 cm, flow 10 cmdiphenylcarbazide solution, made up to the mark with water and mix the solution.

3.3.5. Optical density of the solution is measured after 15−20 min in a cuvette with a layer thickness of 20 mm with mass fraction of chromium from 0.05 to 0.5% and 10 mm with mass fraction of chromium in excess of 0.5% at a wavelength of 546 nm. Solution comparison is the solution of the reference experiment.

3.3.6. The solution in the reference experiment is prepared according to claim.3.3.1, 3.3.3, 3.3.4, using is sample the sample the sample of aluminium. Mass fraction of chromium is calculated according to the calibration schedule.

3.3.7. Construction of calibration graphs

3.3.7.1. When the mass fraction of chromium from 0.05 to 0.5% in seven conical flasks with a capacity of 100 cmis placed hitch aluminum weighing 0.1 g was dissolved in 25 cmof a mixture of acids. Six of them measure 0,5; 1,0; 2,0; 3,0; 4,0; 5,0 cmstandard solution B, which corresponds to 0,00005; 0,0001; 0,0002; 0,0003; 0,0004; 0,0005 g chrome.

3.3.7.2. When the mass fraction of chromium of from 0.5 to 1.0% in seven conical flasks with a capacity of 100 cmis placed hitch aluminum weighing 0.1 g was dissolved in 25 cmof a mixture of acids. Six of them measure 5,0; 6,0; 7,0; 8,0; 9,0; 10,0 cmstandard solution B, which corresponds to 0,0005; 0,0006; 0,0007; 0,0008; 0,0009; 0,001 g chrome.

Z. 3.7.3. In flask add 20−25 cmwater, 5 cmof a solution of silver nitrate, 5 cmsolution naternicola ammonium and continue on PP.3.3.3, 3.3.4, 3.3.5.

The solution in the flask not containing chromium, in each case, is a solution of the reference experiment when constructing the calibration graphs.

According to the obtained values of optical density of the solutions and their corresponding masses of chrome that build of the calibration graphs.

3.4. Processing of the results

3.4.1. Mass fraction of chromium () in percent is calculated by the formula

, (3)

where is the mass of chromium in aliquote part of the solution was found in the calibration schedule g;

 — the weight of the portion of the sample in aliquote part of the solution,

3.4.2. Discrepancies in the results must not exceed the values given in table.2.

Table 2

4. The PHOTOMETRIC METHOD for the DETERMINATION of CHROMIUM (from 0.001 to 0.15%)

4.1. The essence of the method

The method is based on dissolving the sample in a solution of sodium hydroxide, the formation after the neutralization of sulfuric acid and oxidation to the hexavalent chromium with potassium permanganate pink complex with diphenylcarbazide and subsequent measurement of optical density at a wavelength of 546 nm.

4.2. Apparatus, reagents and solutions

Spectrophotometer or photoelectrocolorimeter.

Sodium hydroxide according to GOST 4328, solution 6 mol/DM.

Sulfuric acid according to GOST 4204, density 1.84 g/cmand a solution of 1:1.

Orthophosphoric acid according to GOST 6552, a density of 1.70 g/cm.

Hydrofluoric acid according to GOST 10484.

Nitric acid according to GOST 4461, density 1,35−1,40 g/cm.

Potassium permanganate according to GOST 20490, a solution of 10 g/DM.

The technical rectified ethyl alcohol according to GOST 18300.

1,5-Diphenylcarbazide on the other 6−09−07−1672, a solution of 1 g/DMfreshly prepared: 0.1 g difenilcarbazida placed in a volumetric flask with a capacity of 100 cm, flow 15 cmethyl alcohol and heated in hot water, leave for 15 min, after which the solution was topped to the mark with water and mix.

Aluminium GOST 11069 brand А999.

Chrome metal according to GOST 5905 brand H99.

Standard solutions of chromium.

Solution a: 0.5 g of chromium metal is placed in a conical flask with a capacity of 250 cmand dissolved by heating to 60 cmof sulfuric acid solution and transfer the solution into volumetric flask with a capacity of 500 cm, made up to the mark with water and mix.

1 cmof the solution contains 0.001 g of chromium.

Solution B: 10 cmsolution And placed in a volumetric flask with a capacity of 100 cm, made up to the mark with water and mix.

1 cmof a solution contains 0.0001 g of chromium.

Solution: 10 cmof solution B is placed in a volumetric flask with a capacity of 100 cm, made up to the mark with water and mix.

1 cmof the solution contains 0,00

001 g of chromium.

4.3. Analysis

4.3.1. A portion of the sample weighing 1 g is placed in a conical flask with a capacity of 250 cm, flow 20 cmof sodium hydroxide and dissolve first at room temperature and then under heating.

Upon dissolution of the sample poured 20 cmof sulfuric acid solution and 1 cmof phosphoric acid. Wash walls with water and filter the solution if it is not transparent, in a conical flask with a capacity of 250 cmthrough the filter medium density («white ribbon»). Filter the precipitate was washed 2−3 times with small portions of hot water and drop, if the mass fraction of silicon in the analyzed alloy does not exceed 1%.

4.3.2. When the mass fraction of silicon in excess of 1% of the filter with the sediment was placed in a platinum crucible, dried, incinerated, preventing ignition, and calcined at 500−600 °C for 2−3 min. After cooling in the crucible add four drops of sulphuric acid, 5 cmhydrofluoric acid and nitric acid drop by drop until a clear solution. Next, the solution was evaporated to dryness and the dry residue in the pot pour 2−3 cmof water and 2−3 cmof sulfuric acid solution. If necessary, the solution was filtered and added to the main filtrate.

The filtrate together with the washings transferred to a volumetric flask with a capacity of 100 cm, made up to the mark with water and mix.

4.3.3. In a volumetric flask with a capacity of 100 cmis taken aliquot part of the solution according to the table.3, if necessary, dilute to 50 cmwith water, heated and added dropwise a solution of potassium permanganate until a stable pink color, the solution boiled for 5 min, cooled to room temperature, add 10 cmdiphenylcarbazide solution, made up to the mark with water and mix.

Table 3

4.3.4. Optical density of the solution is measured after 15 min at a wavelength of 546 nm in a cuvette with a layer thickness of 50 mm. Solution comparison the solution serves as the reference experiment.

4.3.5. The solution in the reference experiment is prepared according to claim.4.3.1, 4.3.3 using is sample the sample the sample of aluminium.

Mass fraction of chromium is calculated according to the calibration schedule.

4.3.6. Construction of calibration graphs

4.3.6.1 this. When the mass fraction of chromium from 0.001 to 0.01% in six conical flasks with a capacity of 250 cmis placed a sample of aluminium of mass 1 g and dissolved in 20 cmof sodium hydroxide solution. Then in five flasks measure 1,0; 3,0; 5,0; 7,0; 10,0 cmstandard solution, which corresponds to the 0.00001; 0,00003; 0,00005; 0,00007; 0.0001 g of chromium.

4.3.6.2. When the mass fraction of chromium in excess of 0.01 to 0.15% in nine conical flasks with a capacity of 250 cmis placed a sample of aluminium of mass 1 g and dissolved in 20 cmof sodium hydroxide solution. Then eight flasks measure 1,0; 3,0; 5,0; 7,0; 9,0; 11,0; 13,0; 15,0 cmstandard solution B, which corresponds to 0,0001; 0,0003; 0,0005; 0,0007; 0,0009; 0,0011; 0,0013; 0,0015 g chrome.

4.3.6.3. In the flask poured with 20 cmof sulfuric acid solution and continue at PP.4.3.2; 4.3.3. Solution, not containing chromium, is in each case a solution of the reference experiment when constructing the calibration graphs.

According to the obtained values of optical density of the solutions and their corresponding masses of chrome that build of the calibration graphs.

4.4. Processing of the results

4.4.1. Mass fraction of chromium () in percent is calculated by the formula

, (4)

where is the mass of chromium in aliquote part of the solution was found in the calibration schedule g;

 — the weight of the portion of the sample in aliquote part of the solution,

4.4.2. Discrepancies in the results must not exceed the values given in table.4.

Table 4

5. ATOMIC ABSORPTION METHOD FOR THE DETERMINATION OF CHROMIUM

5.1. The essence of the method

The method is based on dissolving the samples in hydrochloric acid in the presence of hydrogen peroxide and subsequent measurement of the atomic absorption of chromium at a wavelength of 357,9 nm in a reducing flame acetylene-air.

5.2. Apparatus, reagents and solutions

Spectrophotometer of atomic absorption with a radiation source for chromium.

Acetylene according to GOST 5457.

Hydrochloric acid according to GOST 3118, density of 1.19 g/cmand a solution of 1:1, 1:99.

Nitric acid according to GOST 4461, density 1,35−1,40 g/cm.

Sulfuric acid according to GOST 4204, density 1.84 g/cm.

Hydrofluoric acid according to GOST 10484.

Hydrogen peroxide according to GOST 10929.

Nickel chloride according to GOST 4038, a solution of 1 g/DM.

Aluminium GOST 11069 brand А999.

A solution of aluminum 20 g/DM: 10 g of aluminum is placed in a beaker with capacity of 500 cm, add 50 cmof water and small portions of 300 cmof a hydrochloric acid solution of 1:1 and dissolved at a moderate heat, adding 1 cmof solution of chloride Nickel. The solution was cooled to room temperature, transferred to a volumetric flask with a capacity of 500 cm, made up to the mark with water and mix.

Chrome metal according to GOST 5905 brand H99.

Standard solutions of chromium.

Solution a: 1 g of chromium was placed in a conical flask with a capacity of 250 cm, add 50 cmof hydrochloric acid and dissolved by heating. After complete dissolution of the chromium solution was cooled to room temperature, transferred to a measuring flask with volume capacity of 1000 cm, made up to the mark with water and mix.

1 cmof the solution contains 0.001 g of chromium.

Solution B: 10 cmsolution And transferred to a volumetric flask with a capacity of 100 cm, made up to the mark with water and mix.

1 cmof solution B contains 0,00

01 g of chromium.

5.3. Analysis

5.3.1. A portion of sample weighing 0.5 g is placed in a conical flask with a capacity of 250 cm, flow 10 cmof water and then small portions of 25 cmof a solution of hydrochloric acid (1:1). The beaker cover watch glass, heat to completely dissolve the sample, add 3−5 drops of hydrogen peroxide and boil the solution for 3 min.

Watch glass and walls of the flask rinsed with water. The solution was cooled to room temperature, transferred to a volumetric flask with a capacity of 100 cm, made up to the mark with water and mix.

5.3.2. When the mass fraction of silicon is less than 1% solution, if it is not transparent, was filtered through a dry filter medium density (white ribbon) in a beaker, discarding the first portions of the filtrate.

5.3.3. When the mass fraction of silicon in excess of 1% after completion of dissolution according to claim 5.3.1 solution is filtered through a filter medium density (white ribbon) in a volumetric flask with a capacity of 100 cm. The filter cake was washed 3−4 times with hot hydrochloric acid (1:99) in portions of 10 cm(primary filtrate).

The filter with precipitate was placed in a platinum crucible, dried, incinerated, preventing ignition, and calcined at 500−600 °C for 3 min. After cooling, the contents of the crucible add 4 drops of sulfuric acid, 5 cmhydrofluoric acid and nitric acid drop by drop until a clear solution. The solution was then evaporated to dryness, after cooling, the residue moistened with 2−3 cmof water and dissolve in 2−3 cmof hydrochloric acid (1:1) under heating.

The solution is attached to the main filtrate in a volumetric flask with a capacity of 100 cm, made up to the mark with water and mix.

5.3.4. Depending on the mass fraction of chromium according to table.5 select aliquot part of the basic solution, transferred to a volumetric flask with a capacity of 100 cm, add 5 cmof hydrochloric acid (1:1), made up to the mark with water and mix.

Table 5

5.3.5. The solution in the reference experiment is prepared according to PP.5.3.1, 5.3.2, 5.3.3, 5.3.4, using is sample the sample the sample of aluminium.

5.3.6. Construction of calibration graphs

5.3.6.1. When the mass fraction of chromium from 0.01 to 0.1% in six volumetric flasks with a capacity of 100 cmpoured in 25 cmof a solution of aluminium, in five of them measure 0,5; 1,5; 2,5; 3,5; 5,0 cmstandard solution B, which corresponds to 0,00005; 0,00015; 0,00025; 0,00035 full; 0.0005 g of chromium.

5.3.6.2. When the mass fraction of chromium exceeding 0.1 to 0.5% in six volumetric flasks with a capacity of 100 cmpour 5 cmof a solution of aluminium, add 5 cmof hydrochloric acid (1:1), five of them measure 1,0; 2,0; 3,0; 4,0; 5,0 cmstandard solution B, which corresponds to 0,0001; 0,0002; 0,0003; 0,0004; 0.0005 g of chromium.

5.3.6.3. When the mass fraction of chromium in excess of 0.5 to 1.0% in seven volumetric flasks with a capacity of 100 cmpour 2.5 cmof a solution of aluminium 5 cmof hydrochloric acid (1:1), six of them measure 2,5; 3,0; 3,5; 4,0; 4,5; 5,0 cmstandard solution B, which corresponds to 0,00025; 0,0003; 0,00035; 0,0004; 0,00045; 0,0005 g chrome.

5.3.7. The solutions in flasks in PP.5.3.6.1, 5.3.6.2 5.3.6.3 and topped to the mark with water and mix.

5.3.8. The sample solution, solution control experience and solutions to build calibration graphs sprayed in a reducing flame acetylene-air, and measure the atomic absorption of chromium at a wavelength of 357,9 nm.

According to the obtained values of atomic absorption and corresponding mass concentrations of chromium to build the calibration graphs.

Mass concentration of chromium in sample solution and in the solution of control and experience determined by the calibration schedule.

5.4.Processing of the results

5.4.1. Mass fraction of chromium () in percent is calculated by the formula

, (5)

where is the mass concentration of chromium in the sample solution found by the calibration schedule, g/cm;

mass concentration of chromium in solution in the reference experiment, was found in the calibration schedule, g/cm;

 — the volume of the sample solution, cm;

 — the weight of the portion of the sample or the weight of the portion corresponding to aliquote part of the solution, g

.

5.4.2. Discrepancies in the results must not exceed the values given in table.6.

Table 6