Determination of Carbon in low-Carbon Steel A Low-Pressure Gasornetric Method CHARLES E. NESBITT AND J4MES HENDERSOS Carnegie Illinois Steel Corporation, Edgar Thomson Works, Braddock, Po. -4 new apparatus and procedure for determining the carbon content of plain and alloyed steels up to 0.05% carbon, with an accuracy of *O.O003O/c, are described. The procedure requires about one hour for a single determination. It consists of burning a 2-gram sample of steel in a stream of purified oxygen, collecting the carbon dioxide evolved in a special absorber containing a solution of sodium hydroxide, subsequently acidifying this solution, and measuring the carbon dioxide that is evolved under low pressure.
T""
accurate determination of carbon in st,eel has long been a niatt,er of concern. The most important development was a change some 35 years ago from solution methods to direct combust on of t'he sample in purified air or oxygen at elevated temperatures to evolvr the carbon as carbon dioxide, which could be absorbed and weighed. As this met,hod proved both speedy and relatively accurate, its use soon became univc.rsa1 for the determination of carbon in ferrous and nonferrous metals combustible in oxygen, but its general applivation has prrstAntrd several problems, t.h(x solution of which led to modifications in the apparatus and procedure. The methods followtl i n thr steel industry proved entirely satisfactory for application to carbon. ordinary steels, iThich rontain more than O.lOr:c During the last, twenty yrars, many steels containing l w h than 0.1Oc; and in some caws even less than 0.01 C{ carbon halo been developed, and srveral varit,tics of practically pure iron have become of commercial ini; ortance. I t was in the analysis of such materials, containing w r y little carbon, that t,he shortcvmings of thc direct combustion method became so apparent and led Tensen (?d, Murray and ;\shley ( I ) , Wootrn and (;ultiner ( d ) , Zieglvr (61,and others to devise a method of lon--pi~cwui~e combustion, by which extrenit~lysmall amounts of carbon dioxide could be measured. Recently, Stanley and Yensen ( 2 ) have reporttsd another modification, which rcpresrnts an improvement, over the nic.t,hod originally drvi,sed by Tenseri ( 5 ) and later by Ziegler (6). The time for thc, analysis has been reduced to 20 minutes or lws.
/
Figure 1 .
0irec.t (:ornbustion ipparatus
I n the met,hod her(%presented, the authors aimcd at srcuririg the accuracy of the lowpressure combustion procedurr and eliminating thc. shortcomings of t'he direct combustion niet,hod used so univcrsally in the steel industry, especially with respect to such intrrfwing elements as sulfur. They aimed a t reducing the blank to a minimum; at expanding the mixture of gases evolved by nicwx of low pressure, so that the accuracy in measuring the small volumes of carbon dioxide could be greatly improved; at absorbing 100% of the carbon dioxide evolved by design of apparatus and manner of procedure;. and a t correcting the 401
volumes to ztandartl conditionh for temperature and pressure by mwnn of a compensator within the apparatus. APPARATUS
The apparatus for t,he low-pressure combustion method for determining low carbons consists of two parts: Figure 1, t'he universal direct combustion apparatus used in the sterl industry with some modifications drwrihed b(.lo\v, and Figuri, 2, the gasometric apparatus, i n whirh thv cmlion dioxide obtained in an absorbr:r from t he direct combustion apparatus is transferred t o the gasometrir apparatus and t,he carhon dioxide is evolved and determined very acruratrly.
.I (Figure 1 ) is an osygcri t,ank with i t a pressure controls; B is an oxygen-purifying furnace, consisting of a 0.8 cm. (0.75 inch) fused silica tube, packed with copper oxide (CuO), heated by a chrome-nirkel wire-wound furnace, controlled by a rheostat to give a tcmperaturr of approximately 600" ( . C is a L-tuhr with the first k g filled with . h a r i t e (a mixture of sodium hydroxide arid asbrsatos~to remove any carbon dioxide and the, sclcond leg fillcd with Anhydronc (magnesiun perchlorate) to rc'niove any moistuix~. 1) is a mercury manometer for regulating tht. flow of oxygcsri. 8 is a cornbustion tube 1.2 cm. (1.125 inrh) in dianietvr, m i s t a n t t,o iron oxide a t 1450" C. and gas pmrtration. T u i ) ~high in alumina content, have heen found acceptablr.. The eriteringend of thr tuhe is capped Lvith a brass end, usually used in the strel industry. Thia is essentially a connection with a taprred circular end t hrougli rvhich the combustion boat is passed and which is then closed by replacing a cap tapered on the inside to fit and held in place by a sere^ clamp to make the connection prrfrctly gas-tight. This cornbustion tube is heated by two altrrnating current 110-volt Globar units (silicon carbide) or any other material, which will heat, the tuhe to 1.250' C. A rheostat capable of controlling the current t,o produce 25" C. steps from 1100" to 1450" (1. is desirablr. The boats used must be resistant to iron oxide at 1450' ('. and withst,and t,he heat without being too fragile. The sizt. pwferred is approximately 4.9 cm. (4.5 inch ) long, 0.8 m i . (0.75 inch) wide, and 0.6 rm. (0.5 inch) deep. Alumina bedding is desirable. The exit end of the combustion tuhe is a ground gas-tight connection. F is a sulfur-arresting tube filled with activated manganese dioxide of particle size passing t'hrough a 40-mrsh and held on a 100-mesh screen. This rragent is prepared according to (3) and is loosely parked betwern layers of ironized asbestos, reacting very m e r etically wit,h sulfur dioxide and sulfur trioxide. Better efficiency will be obtained, owing to less channeling, if the container is held in an upright position. G is an absorber packed with helical glass rings, the two ball-shaped compartments acting as spray traps. The cup-shaped part above the stopcock is used, when solutions are added to the absorber. H is the gas flow indicator, containing Xvatcr. G (Figure 2) is an absorber, the same as in Figure 1, attached to t'he gasometric apparat,us for transferring the carbon dioxide obtained from the combustion train, in order td determine the amount of carbon dioxide present,. I,, I,, 13,etc., are stopcocks. The manifold from 1, to 19 is 1-mm. tubing with ball and socket ground-glass connections, which are made gas-tight,. J1 and J* I
402
V O L U M E 19, NO. 6
are leveling bulbs, K is the evacuating buret, and L is the measuring buret. M is the compensator used t o correct volumes for standard temperatures (25" C.) and pressure (334 mm.); both L and M are enclosed in a water jacket. N is a water manometer which is very sensit'ive and used in equalizing pressures, when the compensator is used. 0 is a 2OY0 sodium hydroxide pipet, used t o remove the carbon dioxide from the mixture of air, carbon dioxide, and water vapor. PI is an acid wash of pH 4, used t o flush out the apparatus after a determination to eliminate the small traces of hydroxide on the walls of the glass tubing; P2 is an alkaline wash of pH 11.5, used to flush out the manifold to remove the acid from the glassware just before the carbon dioxide is removed from the gas mixture. The manifold from stopcock I2 to IS is filled with mercury, including leveling bulbs J I and,Jn and burets K and L. The mercury is all degassified by loivering the leveling bulbs several times reducing the pressure, and passing the air recovered out of either end of the manifold. With all air eliminated and passageways properly flushed out, the apparatus is ready for a det,ermination. The Compensator is a barometer t,ype, and the pressure can be adjusted by means of stopcock 1 6 to any point below 350 mm. by making connection Ii-ith the receiving buret, K , and nianipu.lating the leveling bulb, JI. For determining carbon in steel, the authors uscd 334 mm. adjusted at 25" C., since at this temperature and pressure, 100 ml. of carbon dioxide from a 2-gram sample are equivalent to and 1 ml. is equivalent to O.O1%jc: The authors prepared the 40% sodium hydroxide by placing selected metallic sodium in a dispensing flask under an atmosphere of carbonate-free air or nitrogen and added carbonate-free wat,er until t,he sodium was converted t o sodium hydroxide. Proper amounts of sodium and wat'er were used t o yield approximately a 40% solution. The solution was allowed to settle out clear and decanted. The clear solution was stored in a dispenser protected by Ascarite tubes and had only a very small trace of carbonates
Before the absorber is attached t o the gasometric apparatus
it is necessary t o flush out that part of the manifold which had
the sodium hydroxide pass through it, with an acid rinse from P degassify the mercury, expel the air recovered through PI, a d fill up the system with mercury from IS to In, including K and L. If necessary the capillary from I 2t o t'he tip is filled with carbonatefree water and the absorber connected. 1 2 and 13 are opened and J 1 is lowered until the mercury level reaches the bottom of K , in order to remove most of the air from the absorber and expel the air from K through PI. This operation is repeated twice. Then 4 ml. of dilute carbonate-free sulfuric acid (1 to 1) are added t,o the cup-shaped part of the absorber, air being carefully excluded and the cup is rinsed three times wit,h earbonate-free n-ater. Before the third rinse is released, conncction is made with carbonate-free air, in order t o empty the cup wit,hout eontaminat,ion. With J1 lowered as far as possible, In and 13 are opened t o connect the absorber \vit,h K . A small flame is applied to the bottom tip of the absorber until the contents are boiling, and gentle heating is c o n h u e d until vapors begin t o condense a t the top of K ; then €2 is closed to the absorber and opened to PI just enough t o sweep the gas in the manifold into K . 1 2 is closed to the absorber and I4 is opened, connecting K with L, and by raising J l the gas mixture is transferred to L, and the last traces of gas are swept out of the manifold. The stopcocks are changed t'o their former posit,ion to connect K with G. With 1 3 open and J 1 lowered as above, the liquid in the absorber is boiled under reduced pressure and about 20 ml. of carbonate-free air are bubbled t,hrough the liquid t o remove the last t'races of carbon dioxide.
PROCEDURE
The determination involves burning the sample in the combustion train, absorbing the carbon dioxide in the absorber, the:i transferring the absorber to the gasometric apparatus, evolving the carbon dioxide by means of acid into the gasometric apparatus, reducing the pressure t o expand the small volume of gases, in order t o read the volume more accurately, then measuring the volume under standard conditions of 25' C. and 334 mm., passing the mixture into the 20% sodium hydroxide pipet to remove the carbon dioxide, and measuring the volume again under standard conditions. The difference after deducting the small blank is the per cent of carbon present. The combustion boat bedded with alumina is heated in the combustion tube in a stream of pure oxygen for 20 minutes a t the temperature to be used in the determination. The combustion of easily fused steels is accomplished a t a temperature as low as l l o O o C., vhile less fusible steels are treated at a temperature as high as 1450" C. The boat is removed from the furnace and kept in a clean covered metal box, until nearly cool, when a 2-gram sample of metal drillings is placed on the alumina bedding, together with 0.1 gram of 30-mesh granular tin, distributed over the drillings. K i t h the oxygen floIving a t the rate of 300 to 350 ml. per minute, the furnace is opened, the boat and sample are placed just inside the furnace end, the furnace is closed, and the boat is preheated for one minute. During this interval the absorber is attached to the exit end of the sulfur-arrester, F , and the inlet end of the gas flow indicator, H . After the absorber has been thoroughly washed and drained, 2 ml. of 40% sodium hydroxide are poured into the cup-shaped part after stopcock I , has been opened; care is taken not to have any of t,he solution drip on the side of t.he cup. After addition of the above solution, 2 ml. of carbonate-free 1vatt.r are used as a rinse and I , is closed. The absorber is rotat,ed IJ the hand to ensure coating the helical rings viith the solution. After the absorber is opened and connected t o the combustion train, the boat is thrust into the hot zone of the combustion tube and the end quickly closed. The rate of florv of the oxygen during the actual combustion of the sample is controlled manually by means of a needle valve on the oxygen regulator, so that the rate does not exceed 60 bubbles per minute as indicated by the oxygen bubbling through H . After 5 minutes the rate is increased t o 300 ml. per minute t o sweep out the last traces of carbon dioxide in the combustion tube. After a minute the oxygen is shut off and the absorber is disconnected and quickly sealed by means of a rubber stopper and stopcock 11,until it is ready t o be attached t o the low-pressure gasometric apparatus.
'I
J iK
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-E
M N I\
Figure 2.
Gasometric Apparatus
403
IUNE 1947
Figure 3. A p p a r a t u s The carbonate-free air is made and stared in two 400-ml. bottlescoiinectedbyglasstubing. Onebottlecontainssmellglassbeads and 20%sodium hydroxide. Air is drawn in and the carbonates are removed. The amount of purified sir used in a determination should bc between 18 and 24 ml., which with tho gas mixture reaches the limitations of the buret for most accurate readmgs. I , is changed from the absorber t o PI carefully to sweep the gas in the manifold into K , then closed. I , is apcned, Jr raised, and Jn lowered, and the gas mixture is transfcrrcd from I< to L by controlling the flow with IS. With I s closed the gas mixture of air, carbon dioridc, and water vapor in L is expanded by lowering J , until the gas pressure is approiimstoly 334 mm. of mercury. Isis then turned t o connect with the water manometer and the final adjustment of the gas pressure to that in the compensator is made by means of the fine leveling screw on the device, which holds the leveling bulbs (Figure 3). Lis allowed to drain 2 minutos and the volume is read with its prcssure balanced exactly against the compensator pressure through the leveled water manometer. After the reading has been recorded, Isis closed, Ja is raised to bring the gas slightly over atmospheric pressure, and the mercury in, the leveling bulb tubing is shut off by turning the screw clamp in tho foot of the apparatus. With I q ' s n d 40open the mercury IS wised in L, the flow being controlled by means of the sercw olsmp. When the water inst shead of the gas volume in the manifold has been shunted towards Ilo, Io is changed quickly, so that all the gas is diverted into the 20% carbon dioxide absorption pipet, 0. While the gas is stored !n the pipet, the manifold and measuring buret arc flushed aut with alkaline water from PZ to remove all traces of acid wator from the walls of the glasswuc. The flush water is forced back to Pz. The gas mixture is passed from 0 t o L two or thrce times to ensure complotu absorption of the carbon dioxide. The gas is drawn off slowly the third time and the strong sodium hydroxide stopped just a t the right-hand end of I,. Alk?line water from P, is usod to sweep thc gas into L. The gas mixture of air and water vapor is measured in t.he same way as shove. From the differenceof the two volumes the determined blank is subtracted and the remainder is the per cent carbon with an rtocuracy of + O.OO( Id%. - -EXPERIMENT.*L
The apparatus ana pruceuuie ueaeribed represent the first successful combination evolved from a sene8 of experiments extending over nearly two years. Numerous changes in design
were necessary before satisfactory performance was obtained. The compensator designed by C. B. Francis WBS the only part that required no alteration. It was chocked for constancy and accuracy, corresponding t o a pressure of 334 mm. and a temperature of 25" C., by measuring the same volume of air stored in the buret over a period of many days at room temperature, which varied from 18' to 30" C. The observed volume, temperature, and pressure were calculated to the volume a t 25' C. and 334 mm. of mercury. The calculated volumes were found to check t h e original volume within *0.02 ml. as measured on a buret less precise than the final one designed. A standard sodium carbonate solution was prepared for t h e purpose of checking the precision and accuracy of the gasometric apparatus from reagent grade anhydrous sodium carbonate dried overnight a t 110' C., due allowance being made for impurities. It was calculated that 1ml. of a sdution containing 1.7653 grams of sodium carbonate per liter would yield I ml. of carbon dioxide measured in the presence of water vapor a t 25' C. and 334 mm. of mercury. Using various aliquots of the standard sodium carbonate solution, which were aecur&ly measured by using the absorber as a weighing bottle, it was found impossible to release and transfer to the measuring buret the last traces of carbon dioxide by boiling, but by passing 20 ml. of carbonate-free air during the boiling theoretical yields were obtained up to 5.0 ml., which corresponds to 0.05% carbon in a %gram sample of metal. This necessitated redesigning L, using B 40-ml. section of larger diameter a t the top and a more accurate reading portion of 53 ml. below, on which one can read 0.05 ml. and with a magnifying glass easily estimate to 0.01 ml. Using high purity sodium carbonate obtained from Alchemia Limited, Montreal, Canada, the authors were able t o check all aliquots up t o 5.0 ml. with deviations from 0.0 to *O.O009% carbon, which was considered too wide B range. Redesigning the absorber with helical glass rings and a change in the procodure improved the range. It was found that all the carbon dioxide was absorbed in mixtures of carbon dioxide and carbonate-free air in a range from 2 to 11%of carbon dioxide, providing the rate of flow through the absorber is properly controlled. The gasometric apparatus now proved a useful tool in
Table Kind of steqi Plain carbon
Method of % AnhiYaiS Szmple Carbon Direct oombustion low- 1 0.0097 pressure gasornetria 0.0095
Deviation, %
0.0099
0,0097 o.oo95
Other low-pressure methods
0.01oo Av. 0.0097 2 0.009 3 0.010 4 0.012 6 0 . 0 1 0
Direct combustion !ow-
1
Other low-pressure methods
2
~
O.OW3
Av. 0.0005 High silicon
pressure ghaometm
0.0032 0.0029 0.0031 0.0029 0.0030 0.0031
A".-
a
-
0.0002
0.0030
Av. 0.0038 Corrosion-resistant Direct combustion I?*heat-resistant p ~ e s ~ u rghmmetrlo e
1 2
0.0220 0.0224 0.0258
3
0.0248
0.0258 0.0248
....
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V O L U M E 19, NO. 6
detecting the small traces of carbon dioxide which go to make up the over-all blank. By checking and making modifications in t h e procedure, the authors were able to reduce the over-all blank t o a reproducible minimum. To test the over-all precision, reproducibility, and accuracy of the method, the authors used two carefully prepared samples, one a carbon steel from the Bureau of Standards and the other a high-silicon steel from the American Rolling Mill Company. Portions of each were sent to four laboratories using the lowpressure method. T o determine whether the apparatus and procedure were applicable to other steels, some samples of stainless, heat-resistant, and corrosion-resistant steels were analyzed. Results of analysis of these steels reported in Table I indicatct t h a t the low-pressure gasonietric method gives results which compare favorably in reproducibility and accuracy n ith thc jesults obtained by other low-pressure niethods.
ACKhOWLEDGRlEYT
The authors gratefully acknowledge the assistance of Guy Burrell and Lloyd Guild of Burrell Technical Supply Company, Pittsburgh, Pa., in supplying special items of glassware required for the experimental work. LITERATURE CITED
(1) Murray, W. M.,and Ashley, S. E. Q., IND.E m . CHEM.,AKAL. E D . , 16, 242 (1944). (2) Stanley, J. K., and Yensen, T. D., Ibid., 17, 699 (1945). (8) U. S. Steel Corp. Chemists, "Sampling and Analysis of Carbon and Alloy Steels,:' Yew York, Reinhold Publishing Corp., 1938. (4) Wooten, L. A, and Guldner, W.G., IXD. E N G .C H E X . ,X h - a ~ . E D . , 14,835 (1942). (5) Yensen, T. D., Trans. A m . Electrochem. Soc., 37, 2 2 i (1920). (6) Ziegler. ?;. A , , I h i d . , 56, 231 (1929).
Determination of Cystine and Cysteine in Altered Human Hair Fibers DOROTHT SANFORD 4 Y D FRED L. HUJIOLLER, Rexenrrh Division, R a y m o n d Laboratories, Znc., S t . P a u l , M i n n .
To determine the amount of cystine in altered human hair in the presence of cysteine, part of the hair is hydrolyzed with 1 to 1 hydrochloric acid for 6 hours at 118" to 120" C. in a closed tube, and the total cysteine plus cystine is determined by the Sullivan method. Another sample is alkylated with the least exposure' to air, using an excess of 1% iodoacetate at pH 8.3, at the temperature of the
0
F THE several methods available for the quantitative esti-
mation of cystine in unaltered human and animal hair fibers, the Sullivan (S), Okuda ( 6 ) , Folin and Looney ( 2 ) , and Brdgcka polarographic (1) methods and their modifications are most frequently used. In the work reported here the Sullivan colorimetric method was used exclusively. To be of any value in the study of the fundamental chemistry of hair waving by the so-called permanent methods, a n i method for the quantitative estimation of cystine must be capable of being modified in such a manner that cystine can be determined in the presence of cysteine. This is necessary in order to follow the degree of reduction produced by the e\periniental alteration of the hair. I n all quantitative cystine methods it is necessary t o hydrolyze the hair with acid for several hours in order t o break the keratin down into its amino acid constituents. Obviously, such treatment may lead to the iroxidation of somt' of the cysteine formed in the experiment if hydrochloric or sulfuric acids are used for hydrolysis, for hair which ha? hcrn reduced by commercial waving solutions always contains traces of heavy metals such as iron or copper and these are efficient catalysts for the reoxidation of cysteine. Since thorough vashing after the reduction step, in the authors' experience, will lead to considerable oxidation of cysteine, the metallic impurities will be carried over into the final hydrolysis mixture. On the other hand, if hydriodic acid is used in the hydrolysis, all cystine is reduced to cysteine. Sullivan, Hess, and Howard (9) have published a method for the estimation of cystine and cysteine in mixtures of these two amino acids and applied it to purified proteins (3). A careful study of their method &s well as of the practical problem of analyziyg
boiling water bath for 30 minutes. The hair is then dried, chopped into small pieces, and hydrolyzed, and the amount of residual cystine is determined by the Sullivan method. Subtracting the latter values from the former gives the amount of cysteine formed. Studies with cold waving reducing and oxidizing solutions show that at room temperature reactions are practically complete within 4 minutes.
altered human hair for these two amino acids in the presence of each other convinced the authors that it was not suitable for their purpose and hence was not tried. Since hydrolysis of the hair is the first step in the determination of cystine, a study was carried out to determine the optimum conditions of hydrolysis-that is, that condition which would cause a minimum amount of destruction of either cystine or cysteine. The open flask method of hydrolysis using 1 to 1 hydrochloric acid, a mixture of formic and hydrochloric acids as recommended by Miller and Du Vigneaud ( 4 ) , or constantboiling hydriodic acid failed to give cystine values in this laboratory for unmodified hair which are consistent with those reported in the literature. Therefore, a study of the sealed tube technique of hydrolysis was undertaken.
T o this end, about 50-mg. samples of accurately weighed hair which had been dried in an oven a t 110' C. for 2 hours were placed in Pyrex test tubes, 5 ml. of 1 to 1 hydrochloric acid (prepared by diluting commercial C.P. hydrochloric acid with an equal volume of water) were added, and the tubes were sealed. In order to prevent accidents, each glass tube was placed inside a piece of gas pipe, closed by screwing caps on both ends. These tubes were then placed in an oven set at 118" to 120" C. for varying lengths of time. After the heating period, the tubes were allowed to cool and opened. The contents were then quantitatively transferred to a 100-ml. beaker and the excess hydrochloric acid was neutralized t o pH 3.5 by the droptvise addition of 5 8 sodium hydroxide; a glass electrode was used to detect the end point. The solutions were then diluted to 100 ml. with a solution of hydrochloric acid adjusted to pH 3.5 and the amount of cystine was determined on an aliquot by the Sullivan method.
