GOST 22536.1-88

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  ГОСТ 22536.1-88

GOST 22536.1−88 (ST SEV 5284−85) carbon Steel and unalloyed cast iron. Methods for determination of total carbon and graphite

GOST 22536.1−88
(ST CMEA 5284−85)

Group B09

STATE STANDARD OF THE USSR

CARBON STEEL AND UNALLOYED CAST IRON

Methods for determination of total carbon and graphite

Carbon steel and unalloyed cast iron.
Methods for determination of general carbon and graphite

AXTU 0809

Valid from 01.01.90
to 01.07.95*
______________________________
* Expiration removed
Protocol N 4−93 inter-state Council
for standardization, Metrology and certification.
(IUS N 4, 1994). — Note the CODE.

INFORMATION DATA

1. DEVELOPED AND INTRODUCED by the Ministry of ferrous metallurgy of the USSR

PERFORMERS

D. K. Nesterov, PhD. tech. Sciences; S. I. Rudyuk, PhD. tech. Sciences; S. V. Spirina, PhD. chem. Sciences (head of subject); V. F. Kovalenko, PhD. tech. science; N.N. Gritsenko, PhD. chem. Sciences; L. I. birch

2. APPROVED AND put INTO EFFECT by Decision of the USSR State Committee for standards from 25.08.88 N 3018

3. The standard complies ST SEV 5284−85 in part of carbon steel and unalloyed cast iron

4. REPLACE GOST 22536.1−77

5. REFERENCE NORMATIVE AND TECHNICAL DOCUMENTS

This standard sets by a gas-volume, coulometric methods and the method of infrared spectroscopy determination of total carbon and graphite in carbon steel and unalloyed cast iron for the mass concentration of carbon and graphite from 0.01 to 5.0%.

1. GENERAL REQUIREMENTS

1.1. General requirements for methods of analysis GOST 22536.0−87.

1.2. The error analysis result (at p = 0.95) does not exceed the limit given in table. 1 and 2, under the following conditions:

the discrepancy between the results of two (three) parallel dimensions should not exceed (with a confidence probability =0,95) of the values given in table.1 or 2;

played in the standard sample, the value of the mass fraction of carbon should not vary from certified more than acceptable (at a confidence level =0,85) the value given in table.1 or 2.

If any of the above conditions, a second measurement of the mass fraction of carbon. If in repeated measurements the precision requirement of the results are not met, the results of the analysis recognize the incorrect measurements cease to identify and eliminate the causes of violation of the normal course of analysis.

The divergence of the two middle results of an analysis performed under different conditions (for example, when the control intralaboratory reproducibility) shall not exceed (with a confidence probability =0,95) of the values given in table.1, 2.

Table 1

Table 2

2. BY A GAS-VOLUME METHOD

2.1. The essence of the method

The method is based on the combustion of a sample of steel or iron in a current of oxygen at 1250−1350 °C with subsequent absorption of the formed carbon dioxide with a solution of potassium hydroxide (sodium).

Mass fraction of carbon is determined by difference of the initial volume of gas and volume of gas obtained after the carbon dioxide absorption by a solution of potassium hydroxide (sodium).

2.2. Determination of carbon with the use of audiometry scale up to 1.5% carbon

2.2.1. Equipment and reagents

Installation by a gas-volume for the determination of carbon (see drawing) consisting of a cylinder with oxygen or coloradobased, equipped with a pressure reducing valve for start-up and regulate the flow of oxygen 1; a gas washing bottle containing potassium permanganate solution with a mass concentration of 40 g/lsolution of potassium hydroxide (sodium) with the mass concentration of 400 g/DM2; a gas washing bottle with sulfuric acid 3 (it is allowed to carry out dry cleaning of oxygen); it is bells 2 and 3 are used gorkaltseva tube, the column Astarita and a V-shaped tube, contains the first half (downstream) asbestos, impregnated with manganese dioxide, and the second — anhydro; horizontal tube furnace with silicafume heaters, providing heating to a temperature of 1350 °C 4; a metal casing, which enclosed the furnace 5; regulator type PSR or other similar type 6; voltage regulator type RNO-250−10 or similar type, 7; of porcelain or refractory mullite tube with a length of 750−800 mm with an inner diameter of 20−22 mm, the ends of which must project from the furnace is not less than 200 mm on each side 8; boats unglazed porcelain GOST 9147−80 9; glass tap, by which regulate the flow rate of oxygen 10; a glass tube (spherical or V-shaped), filled with glass or cotton wool to retain solid oxides, entrained from the furnace by a current of oxygen 11; a gas washing bottle with a solution of potassium dichromate in sulfuric acid for absorption of sulfur dioxide (which is allowed to be used as a filter-absorber glass tube filled with manganese dioxide or peroxide granules) 12; gas analyzer Gow-1 or KGA-4, includes a refrigerator coil to cool the incoming furnace gas mixture (CO+ O) 13; two-way tap that connects audiometer with a refrigerator, an absorption vessel and the atmosphere 14; single tap connecting audiometer with the atmosphere 15; 16 audiometry a total capacity of 250 cm. Audiometr has double walls, the space between which is filled with water, thereby reducing the influence of ambient temperature. Here is a hollow float which, when filling in audiometry liquid rises and locks the top hole. The narrow part of audiometry attached is a sliding scale for determining the change in volume of gases during combustion of the sample. The scale corresponds only to audiometry to which it is attached. Transfer it to another audiometer invalid. The division of the scale corresponds to the percentage of carbon in 1 g of the test substance. Audiometry graduated at a temperature of 16 or 20 °C and atmospheric pressure 7448 PA (760 mm Hg.St.), therefore, for other conditions enter a correction for temperature and atmospheric pressure in the appropriate table attached to the detector; a thermometer for measuring the temperature of the gas 17; a vessel for absorption of carbon dioxide 18, is filled with a solution of potassium hydroxide (sodium) and provided with a slide valve floats, which close the sink when it is filled with hydroxide solution. This eliminates the possibility of getting solution of potassium hydroxide (sodium) from the absorber audiometer. The absorption vessel is connected with a cylindrical vessel during the filling of the absorption vessel, a gas mixture is pumped alkali solution; the surge flask 19 with a capacity of 600−700 cmfor transferring the gas mixture of the gas-measuring burette into the sink. The surge bottle is filled with packing liquid.

Drawing

Barometer.

Desiccator, according to GOST 25336−82.

Muffle furnace type SNOL according to normative-technical documentation or any other type providing a heating temperature not lower than 900 °C. Porcelain boat pre-calcined at a temperature not lower than 900 °C for 24 h, if the calcination is carried out in a current of oxygen, enough for 3−4 h. the Calcined boats remain in the desiccator containing the hydroxide of barium. Socket cover of the desiccator should not cover lubricating substances. The hook is made of low-carbon heat-resistant wire with a diameter of 3−5 mm, a length of 500−600 mm, with which the boat is introduced into the tube for flaring and extracted from it.

The oxygen of GOST 5583−78.

Sulfuric acid GOST 4204−77, a solution with a mass concentration of 20 g/DMand dilute 4:1.

Potassium permanganate according to GOST 20490−75, a solution with a mass concentration of 40 g/DMthe potassium hydroxide solution with the mass concentration of 400 g/DM.

Potassium hydroxide according to GOST 24363−80 or sodium hydroxide according to GOST 4328−77, a solution with a mass concentration of 400 g/DM.

Potassium dichromate according to GOST 4220−75, a solution with a mass concentration of 150 g/lin sulphuric acid, diluted 4:1.

Sodium chloride according to GOST 4233−77.

The indicator methyl orange, aqueous solution with a mass concentration of 1 g/DM.

The calcium chloride.

Soda lime or soda asbestos (Askari).

The rate of anhydrous magnesium (anhydro), Mg (СlO).

Gidroperit.

Manganese dioxide according to GOST 4470−79.

Barium hydroxide according to GOST 4107−78.

The ethyl ether according to GOST 22300−76.

Rectified ethyl alcohol GOST 18300−87.

Acetone according to GOST 2603−79.

Packing liquid: sulfuric acid solution with a mass concentration of 20 g/DMsolution of sodium chloride with a mass concentration of 260 g/DMacidified with 2−3 drops of sulfuric acid. In both cases, the solutions contain 2−3 drops of methyl orange solution.

Marshes: tin GOST 860−75 or copper according to GOST 546−79, iron carbonyl for Radiotechnical GOST 13610−79, as well as oxides of these metals.

Allowed the use of other flooded areas. All marshes should be checked for carbon content, which should not exceed the value of permissible differences for the corresponding values of the mass fraction of carbon, are given in table. 1 Il

and 2.

2.2.2. Preparation for assay

Installation (see drawing) lead to a working state. Heat oven to operating temperature and calcined porcelain tube throughout its length. Then the ends of the tubes closed from both sides a well-fitting rubber corks or metal bars, in which hole is inserted a glass or brass tube. Check the tightness of the installation. For this purpose one end of the porcelain tube connecting a rubber hose through the funnel to clean oxygen with an oxygen cylinder containing oxygen and the second gas analyzer. After the installation check for complete sealing at the operating temperature of the furnace. The absorption vessel is filled with a solution of potassium hydroxide (sodium), and the surge flask are poured 400−500 cmsodium chloride solution or sulfuric acid solution. The transition of the red color of the indicator in yellow indicates the penetration of audiometr of the alkali solution from the absorption vessel. In this case, the liquid in the burette should be replaced immediately fresh.

After each replacement liquid burned several samples with high carbon content and flow gases through audiometr the surge bottle to saturate the carbon dioxide contained in it solution, otherwise the first results of determination of carbon after filling equalization flask with fresh liquid may be underestimated.

Then double tap 14 is put in a position of uncoupling audiometer, absorption vessel, and a refrigerator. Opening the valve 15, which connects audiometer with the atmosphere, raise the levelling bottle; eudiometer is filled with fluid. After this, valve 15 is closed, and the tap 14 is put in a situation in which audiometr connects the absorption vessel.

Lowering the levelling bottle and drain it of fluid from audiometry. It increases the level of alkaline solution in the absorption vessel and the float rises. As soon as the float will close the exit from the absorption vessel, the valves 14 and 15 put in a position in which audiometer is connected with the atmosphere. Raising the levelling bottle, fill eudiometer liquid to the upper limit, then close the valve 15 and the surge flask is lowered.

If the installation is sealed, the levels of solutions in the absorption vessel and audiometry remain unchanged during the 10−15 min If the fluid in audiometry is omitted, it means that the sensor is leaking. It should be disassembled, thoroughly wipe the faucets with soft cloth lubricated with vacuum grease and repeat the check.

The wool in the bowl 11 should be replaced as needed.

To control the correctness of the results of the analysis at the beginning and every 2−3 hours burn 2−3 sample standard sample of steel or iron in the presence of flux. Then burn the flux linkage for the establishment of amendments in the reference experiment.

Before combustion of the sample set the zero level of the solution in audiometry and surge bottle. To do this, turning off 14, connect audiometer with the atmosphere and allow the liquid in the burette and levelling the flask to set at the same level.

The movable scale of audiometry set so that the meniscus of the liquid in both vessels were at the zero scale division. The zero position of the test solutions before each determination of carbon.

Before combustion of each sample oven is connected to the atmosphere through the valve 14 and opening the valve 10, connecting the furnace with the system for the purification of oxygen flow oxygen for 1−2 minutes, then close the valves 10 and 14.

If necessary, immediately before analysis, calcined porcelain boat in a current of oxygen at the operating temperature in 3−5 minutes, cool and store them in a desiccator.

2.2.3. Analysis

A sample weight of 0.5−1.0 g of steel, or 0.25−0.50 g of cast iron placed in a porcelain boat, the top is covered with a uniform layer of one of the flooded areas in the amount of 0.5−1.0 g and a hook is introduced into the most heated portion of the porcelain tube, the end of which is closed with a stopper, thus connecting the furnace with an oxygen tank and a gas analyzer.

In the analysis of the carbon steel is allowed to carry out the burning of the sample the sample without flux.

After 10−20 s after the entry of the boat into the tube (the time required to boat and hitch took the temperature of the furnace) is passed through the tube pre-purified oxygen at a rate of transmittance of 0.2−0.4 DM/min (0,03 kgf/cm) for 1 min.

With the help of a crane 14 for some time, disconnect the refrigerator 13 and audiometr 16 so that the burning took place, with some excess oxygen. Then the crane 14 is put in a position in which the gas mixture enters audiometer. The gas mixture was fed to audiometr during combustion of the sample periodically with the help of clip.

The surge bottle is put on the stand at the top of the detector and leave it in this position until the oxygen and the combustion products to displace fluid from the upper part of audiometry. Then put the surge flask in the lower position (on the stand) and leave in this position until, until the liquid level falls approximately to the scale value of 0.20. Disconnect the plug with the porcelain tube and the tube is removed from the boat. The fluid level should be set audiometer at the zero scale division, and the surge flask — on the same horizontal with him. Then, changing the position of the valve 14, the gas mixture is transferred from audiometer in the absorption vessel 18, making sure that at the top of audiometry was free of gas bubbles.

From the absorption vessel 18, the remaining gas is pumped again to audiometer. This operation is repeated again. Then set the tap 14 in a position of complete separation audiometry the absorption vessel and measure the volume of gas in eudiometry. To this end, the liquid in the surge flask and eudiometer set on one level, provide exposure 1 min, to drain the liquid remaining on the walls of audiometer, then, to match exactly the meniscus is, on a scale of audiometry determine the amount of absorbed carbon dioxide (proportional to the carbon content in the analyzed material), recording the corresponding division of the scale. The rubber hose connecting audiometer with equalization flask should be in a horizontal position on the table. Note the temperature of the gas in the burette and atmospheric pressure. Release of gas in the burette and prepare the apparatus for subsequent incineration.

The test temperature and pressure is carried out every 1.0−1.5 h.

In the analysis of high carbon steel and cast iron to control the combustion efficiency of afterburning carbon is additionally weighed, re-take away the gas from the furnace and determine the content of carbon. The results obtained in the two extractions, summarize and accept the final result.

2.3. Determination of carbon (0,01−0,20%) with the use of audiometry scale to 0.25% carbon

2.3.1. Equipment and reagents

Equipment, reagents, solutions and diagram of the installation according to claim 2.2.1 with additions.

Electric dubtronica.

Porcelain or mullite refractory tube No. 7 or No. 8, unglazed, with a length of 750−800 mm, an inner diameter of 20−22 mm. One of them is used for purification of oxygen impurities containing carbon, the other for the combustion of batches of steel.

For cleaning of gases from the first tube, are two washing flasks filled with a solution of barium hydroxide to absorb carbon dioxide contained in the technical oxygen, with concentrated sulfuric acid to absorb moisture.

Audiometer with scale 0,25% of carbon.

Equalization flask with side tube filled with sulfuric acid.

Barium hydroxide according to GOST 4107−78, a solution with a mass concentration of 50 g/DM.

2.3.2. Training equipment

Before commencing work the installing drive. The ends of the porcelain tubes closed with rubber stoppers embedded with glass or brass tubes. One end of the porcelain tube, intended for the purification of oxygen impurities containing carbon, connect a rubber hose through cleaning bottles with the oxygen tank, the other end through the flask for purification of gases connected to one end of the porcelain tube that is designed to burn batches. The second end of the tube to burn through a rubber hose connected to the gas analyzer. After that, the installation check for leaks at operating temperature as given in claim 2.2.2.

2.3.3. Analysis

The weight of steel weight of 1 g, previously washed with ether, ethyl alcohol or acetone and dried, placed in a porcelain boat, pre-calcined in flowing oxygen at operating temperature and then carry out the analysis as given in claim 2.2.3.

2.4. Processing of the results

2.4.1. Find a correction for the temperature and pressure conditions, which was used to determine the mass fraction of carbon.

Mass fraction of carbon () in percent is calculated by the formula

,

where and is an indication of the scale of audiometry after absorption of carbon dioxide from the combustion of batches of sample and reference experiment, respectively, %;

 — correction factor for temperature and atmospheric pressure, is selected in accordance with the terms of calibration of the instrument;

 — the weight of the portion of the sample,

2.4.2. Norms of accuracy and norms control the accuracy of determining the mass fraction of carbon steel is given in table. 1, for iron in table.2.

3. COULOMETRIC METHOD

3.1. The essence of the method

The method is based on the combustion of the sample the sample in flowing oxygen at a temperature of 1250−1350 °C, the absorption of the formed carbon dioxide absorption by a solution with a particular initial pH value and subsequent measurement in the apparatus for coulometric titration, is necessary to restore the original pH value of the electricity quantity, which is proportional to the mass fraction of carbon in the linkage sample.

3.2. Equipment and reagents

Coulometric installing an 7529, 7560 EN with all accessories (comonomer, absorption vessels, pH meter, corrector mass) or any other type, providing the necessary accuracy of the analysis.

Horizontal tube furnace of any type, providing heating to a temperature of 1350 °C.

The oxygen of GOST 5583−78.

Tubes of refractory porcelain or mullite — normative-technical documentation with a length of 600−800 mm, an inner diameter of 20−22 mm.

Boat porcelain with GOST 9147−80.

Muffle furnace type SNOL according to normative-technical documentation or any other type providing a heating temperature not lower than 900 °C. Pumps porcelain pre-calcined at temperatures below 900 °C during the day, if the calcination is carried out in a current of oxygen, enough for 3−4 h. the Calcined boats remain in the desiccator containing the hydroxide of barium. Socket cover of the desiccator should not cover the lubricant.

If necessary, immediately before analysis, calcined boats in a current of oxygen at the operating temperature for 3−5 min. Calcined boats stored in a desiccator.

Manganese dioxide according to GOST 4470−79.

Lead granulated according to normative-technical documentation.

Gidroperit according to normative-technical documentation.

The technical rectified ethyl alcohol GOST 18300−87.

The ethyl ether according to GOST 22300−76.

Acetone according to GOST 2603−79.

Absorption and support solutions are prepared in accordance with the type of the used coulometric setup.

Marshes: copper GOST 546−79, tin GOST 860−75, iron carbonyl for Radiotechnical GOST 13610−79 or oxides of these metals. Allowed the use of other flooded areas. Marshes should be checked for carbon content. Mass fraction of carbon in the flux should not exceed the value of permissible differences for the corresponding values of the mass fraction of carbon, are given in table. 1 and 2.

3.3. Analysis

The device is ready to work in accordance with the instructions and carry out the calibration by standard samples. To remove traces of carbon from the plant before the analysis, through installation allow oxygen and calcined up. The transmission of oxygen and the calcining tube is carried out to obtain the minimum continuous readings.

When analyzing samples with a mass fraction of carbon less than 0.10% of the required additional purification from sulfur dioxide. For this purpose, the filter-absorber between the absorption vessel and the stove, put the manganese dioxide or gidroperit. Use the lead to eliminate the effect of sulphur when the mass fraction of less than 0.03%. To do this, after the establishment of the porcelain tube, and at each subsequent replacement burn a portion of the lead.

To control the correctness of the results of the analysis before beginning work and every 2−3 h during work burn 2−3 sample standard sample of steel and cast iron with a known mass fraction of carbon and close to define.

Weighed samples of ground mounted depending on the type of coulometric setup, placed in a porcelain boat and covered with a uniform layer of flux. The mass ratio of the batches of flux and sample is 0.5:1 or 1:1.

In the analysis of the carbon steel is allowed to carry out the burning of the sample the sample without flux.

In the analysis of steel with a mass fraction of carbon of less than 0.2% chips samples if necessary, washed with ether or alcohol, or with acetone, dried and taken charge.

A boat with linkage and flux is placed in the working part of the furnace and burning the sample in flowing oxygen at a temperature of 1250−1350 °C.

The analysis is complete, if the readings do not change during 1 min or change the amount of idle accounts tool.

3.4. Processing of the results

Mass fraction of carbon is determined by the digital display of the analyzer minus the result of the reference experiment.

3.5. Norms of accuracy and norms control the accuracy of determining the mass fraction of carbon is given in table. 1 and 2. The method used in the dispute in the assessment of quality carbon steel and unalloyed cast iron.

4. THE METHOD OF INFRARED SPECTROSCOPY

4.1. The essence of the method

The method is based on the combustion of the sample the sample in flowing oxygen at a temperature of 1350−1700 °C and determining the quantity of formed carbon dioxide by measuring the absorbed infrared radiation to them.

4.2. Equipment and reagents

Automatic analyzer based on absorption of infrared radiation, of any type complete with all accessories.

The flux and ancillary materials depending on the type of the used analyzer.

4.3. Analysis

Before analysis is carried out the calibration of an instrument with standard samples.

The analysis is conducted depending on the type of analyzer.

To control the correctness of the results of the analysis before beginning work and every 2−3 h during work burn 2−3 sample standard sample of steel or cast iron with a known mass fraction of carbon and close to define.

4.4. Processing of the results

4.4.1. Mass fraction of carbon is determined by digital signal analyzer minus the result of the reference experiment.

4.4.2. Norms of accuracy and norms control the accuracy of determining the mass fraction of carbon is given in table. 1 and 2.

5. METHOD OF DETERMINING GRAPHITE

5.1. The essence of the method

The method is based on the property of graphite is not dissolved when dissolving samples of iron or steel in dilute nitric acid. The precipitate was filtered off, dried, burnt in a current of oxygen, and determine the mass percent of graphite by a gas-volume or coulometric method, or by infrared spectroscopy.

5.2. Equipment and reagents

Apparatus, reagents and solutions — p. 2.2.1, with additions.

Pump Komovskogo or any other type — to create a vacuum during the filtration.

Asbestos for filtering. Fibrous asbestos is cut into pieces with a length of approximately 10 mm and treated by boiling with hydrochloric acid by the GOST 3118−77 as long as new portions of the acid will not cease to be painted in yellow color, indicating the presence of iron. Then the asbestos is washed from acid with hot water, dried and calcined at 800−850 °C for 0.5−1.0 hours until complete burnout of carbon. You need to check the asbestos content of carbon, burning it in the oven in the same amount as in the analysis.

Nitric acid GOST 4461−77 diluted 1:1.

Hydrofluoric acid according to GOST 10484−78.

The indicator diphenylamine according to GOST 5825−70: 1 g diphenylamine dissolved in 100 cmof sulphuric acid according to GOST 4204−77, or 100 cmof phosphoric acid according to GOST 6552−80.

5.3. Analysis

Taken from the analysis of chips of cast iron are triturated in an agate mortar and sieved through a sieve with holes size of 0.10 mm. Remaining large particles rubbing until, until all the chips will not pass through a sieve. The sample average.

Steel shavings, designed to determine the carbon content, annealing, do not RUB.

Prepared chips of cast iron or steel mass depending on the assumed mass fraction of graphite (see table. 3) is placed in a beaker with a capacity of 200−250 cm, and dissolved in nitric acid (1:1), covered with a glass watch glass. If the dissolution proceeds rapidly, the glass is immersed in a bowl of cold water and after the cessation of violent reaction continue dissolving with a moderate heat.

Table 3

If you roll a considerable precipitate of silicic acid, add 1−2 cmhydrofluoric acid and heating was continued.

Dissolution is complete when terminated selection of brown fumes of nitrogen oxides (in this case turbid sediment should slowly sink to the bottom of the glass). In this case, the contents brought to the boil, pour 100 cmof hot water and again bring to a boil. The hot solution is poured through an asbestos filter, specially treated and placed in a porcelain crucible with a mesh bottom, or through a glass funnel porcelain filtration plate. Filtration is carried out under vacuum. The precipitate of graphite is washed in a glass 4−5 times with hot water acidified with a few drops of nitric acid, and transferred to a filter. Adhering particles of the precipitate is removed with a piece of asbestos with glass rods and forceps. After that, the precipitate and the asbestos filter, washed with hot water of 70−80 °C to negative reactions to nitric acid (when mixed on a porcelain plate one drop of washing liquid with two drops of diphenylamine must not be staining).

The precipitate of graphite, together with the asbestos quantitatively transferred with tweezers into a porcelain boat, pre-calcined in flowing oxygen, and dried in a drying Cabinet at 105−110 °C for 30−40 min.

The dried precipitate of graphite is burned in a tube furnace, and the further identification done by a gas-volume method (sect. 2) or coulometric method (sect. 3), or infrared spectroscopy method (sect.4).

5.4. Processing of the results

5.4.1. Mass fraction of graphite () percentage to determine by a gas-volume method is calculated by the formula

,

where and is an indication of the scale of audiometry after the absorption of carbon dioxide from the combustion of batches of sample and reference experiment, respectively;

 — correction factor for temperature and pressure;

 — the weight of the portion,

Mass fraction of graphite () percentage in determining its coulometric method when the sample mass of 0.5 g corresponds to the indication of the digital display device subject to the control of experience; while the sample mass of 0.25 g mass fraction of graphite is calculated by the formula

,

when mounting a mass of 1.0 g mass fraction of carbon is calculated by the formula

,

where and  — the testimony of the scoreboard during the combustion of sample sample and control sample, respectively.

5.4.2. Norms of accuracy and norms of accuracy control of determination of graphite are given in table. 2.