Anal. Chem., 135th Meeting, ACS, Boston, April 1959. (58) Miller, It. D., J.Assoc. Agr. Chemists 31, 373 (1918). (59) hfisson, G., Chemiker-Ztg. 32, 633 (1908). (60) Muller, It. H., ASAL. CHEM. 30, No. 1, 53 A (1958). (61) I’errin, C. H., Zbid., 21, 984 (1949). (62) Perrin, C. H., J. Assoc. Ojic. Agr. Chemzsts 41,758 (1958). (63) Reuss, J. L., Graves, H. B., Northcott. E..“ I ~ e v e l o ~ m e noft a Continuous ‘l.,C&,haly&r,” Meeting of Am.
Inst. Mining Engrs., Sew York, February 1958.
(64) Saint-Chamant, H. de, Vigier, R . , Bull. SOC. chzm. France 1954, 180. (65) Schall, E. I)., ANAL. CHEJI. 29, 1044 (1957). (66) Scharrer, K., Kuhn, H., Luttmer, J., Landwzrtsch. Forsch. 8, 26 (1955). (67) Scheel, K., Angew. Chem. 66, 102 (1954). (68) Shuey, P. McG., J . Assoc. O B . Agr. Chemists 38, 761 ( 1955). (69) Stettbacher, A., 21.Iatt. Gebaete Lebensm. u. Hyg. 34,90 (1943). (70) Stout, P. It., Johnson, C. M., Yearbook Agr., U. s. Dept. Agr. 1957, p. 139.
(71) Taylor, D. S., J . .lssoc. Ogic. A g r . Chemzsts 32, 422 (1919). (72) Thornton, S. F., Conf. on Chem. Control Problems, p. 37, S a t l . l’lant Food Inst., Washington, U. C., 1957. (73) Van Thiel, H. L,Tucker, W. J., J. Agr. Food Chem. 5, 442 (1Y.57). (74) Watt, G. W., Chrisp, J. U., ANAL. CHEM.26, 452 (1951). (75) Wilson, H. N., Analyst 76, 65 (1951); 79, 535 (1954). (76) Wilson, H. N.,Lees, I). S., Broomfield, W., Zbid., 76,355 (1951).
RECEIVEDfor reviem Xugllst 2 5 , 1959. Accepted August 25, 1059.
Some Recent Developments and Current Problems in Metal Analysis ROBERT M. FOWLER Technology Department, Union Carbide Metals Co., Division of Union Carbide Corp., Niagara Falls, N.
,Determination of carbon in steel is discussed as an example of the progress in metal analysis in 40 years. The real revolution has come in the last 15 years with the direct-reading spectrograph and x-ray spectrometer. The future of analytical chemistry lies in development of specialized tools.
T
Fisher Award honors Dr. Hoffman for his contributions to analytical chemistry, which have been many, but does not mention the great influence his clear and direct approach to problems has had on the thinking of others. It may be interesting to consider the advances in metal analysis that have been macle during the time the Award winner has been concerned with this field. His first publication was in 1921, on the determination of cobalt and nickel in steel (6). This was a thorough classical approach to the problem. He showed that to obtain precise results a nuniber of separations and recoveries had to be made. It was a lengthy and time-consuming procedure, but the important thirg a t that time was not how long it took but that it was possible, b y applying all the necessary corrections, t o obtain prrcise results. I would estimate that 6 to 10 determinations by this procedure ir-ould require 3 mandays. Although many papers have been published since on this determination, the procedure developed in 1920 was the standard procedure for cobalt until the late 30’s and is still used. Because the field of metal analysis is so very broad, it is impossible to even mention all the. progress that has been HE
made in the nearly 40 years since Dr. Hoffman published his first paper. Instead of trying to cover the field, I would like to consider only one determination-the estimation of carbon in steel as a n example of the progress that has been made-chosen because in 1920 i t was one of the fastest determinations the steel chemist could make. CARBON IN STEEL
At that time, the bible of the steel chemist was Blair’s Chrniical Analysis of Iron and Steel (3) which originally appeared in 1888 and had gone through seven editions by 1920. Incidentally, the seventh edition makes no mention of standard samples. Even common volumetric solutions were standardized by very time-consuming methods that lacked precision except in the hands of a very skilled ninnipulator. nIost steel methods were suitable only for plain carbon steels and, even then, in many cases, the situation vas little better than the somewhat earlier experience of F. W, Sniither of the Sational Bureau of Standards. Sniither a s employed a t a sninll blast furnace to determine carbon in pig iron. There was also an old fellow named Jim n-ho estimated the carbon and gradcd the iron by fracturing a pig and looking a t the fracture. As Smither told it, it was many nioiiths before he could convince the blast furnace superintendent, in the event of a dispute, that the chemically determined figure for the carbon content was the correct one. While platinuni had been relatively cheap and some of the steel works still used platinum combustion tubes and
Y.
boats, the common reagents were of doubtful quality. Fortunately, most of the steels were either plain carbon or low alloy. Imagine trying to detcrmine carbon in one of the highly alloyed materials n’e run routinely today using a gas-fired furnace with a maximum temperature of perhaps 1100” C. as recommended by Blair. The precision some of these early workers attained was attained a t a cost of time which made most of their analysc~historical. Many will recall H. V, Churchill’s definition of a control analysis as one that is received by the mctallurgist i n time for him to do sonicthirig about it, and a historical analj.sis as one rcceivetl too late for the customer to do anj’thing about it. If one follon-ed Blair’s procedure, a carbon noultl rcquire a t least a n hour. Of course, the chemist made more than eight per day bccausc 8-hour days n’ere unknown then, and faster procedures than those dmcribed by Blair were used in some places. Many people h a w contributctl t o the progress in this ratlwr simple operation of burning a n-cighetl amount of a metal in oxygcn and estimating the amount of carbon dioxide formed. Fen. radically new idcns have been introduced, but as progress \KIF macle in furnaces and devices for purifying an(l estimating the carbon dioxide, the timc has been shortcncd and the precision improved. The nickel-chrorre alloy resistor furnace n-as a big iniprowment over the gas-fired furnace and tl:c silicon carbide resistor furnaces were a further improvement. These furnaces rcquiretl superior combustion tubes ant1 boats of more refractory matcrials, but now for low-carbon materials a new difVOL. 31, NO. 12, DECEMBER 1959
1949
ficulty appeared. Good as the new refractory tubes were, the sample was heated by transmission, so the tube n'as always hotter than the sample. This led to blank troubles and shortened tube life. With the advent of small induction furnaces, the sample could be heated faster than the tube, with the resultant smaller blank, and a cheaper tube could be used. This materially reduced blanks due to adsorption and desorption of carbon dioxide by the ceramic tube. Likewise, for absorption of the C02, soda asbestos was a big improvement over soda lime or the cunibersome Liebig bulb recommended by Blair, Those who had to clean P205out of a n absorption bulb welcomed the more convenient magnesium perchlorate. But n-eighing a n ahsorption bulb n-as too slow, so volumetric apparatus for estimating the carbon dioxide was developed and is widely used. Meanwhile, lower and lower carbon contents became of interest to the metallurgist, and this led to bhe conductometric and gasometric methods. Khile carbon determinations in less than 5 minutes ha1.e become common, the demand is for faster and faster analyses. Because much greater progress has been made in the estimation of most of the other elements in metals, even ivith all the improvements, carbon has changed from one of the fastest analyses to one of the slowest. To meet the demand, future progress in this area will come from indirect spectrographic or x-ray niethotls, rather than from further refinements of t,he combust'ion method. llagnetic methods are widely used for preliniiiiary carbon estiniations. K h e n the .In,ard winner and his colleagues were writing their classic book on steel analysis, they inquired about the utility of a magnetic carbon estimation device that a prominent steel chemist had imported a few years before. With his reply to their inquiry. he enclosed the brass nameplate from this device and stated that this was all that was left of it and he hoped lie never s a x even that again. Y r t three decades later, such devices arc widely and successfully usrd to control carbon in Fteel. STANDARDS
The r c d revolution in nic'tnl annly~is has come in the last 1.5 years 115th the advent of the direct-rrading speetrograph and the x-ray spectrometer. These have made true control analyws for nietallic elements possible. *It the same time, thry have increased the pressure on the Award n-inner and his colleagues a t the Sational Bureau of Standards-for standards to use as bench marks. Kearly all the nen' rapid niet)hods measure only differences, so 1950
ANALYTICAL CHEMISTRY
must be calibrated on a standard or standards. As craftsmanship has declined in the machining of metals with the advent of automatic controls on machine tools, likewise, there has been a decline in analytical craftsnianship to the point where the preparation of standards or, rather, finding people and methods to prepare standards sufficiently precise for the new instrumental methods, is a problem. Fortunately, the Sational Bureau of Standards has continued and expanded its very valuable ivork in this area. The need is increasing. For example, a proposed specification for one of the less common metals calls for analysis for 22 other elements, most of them in the less than 100 p.p.m. range. Our Bureau of Standards has done a magnificent job in this area, which has been copied by several other governments, including the R u=ians. .~.~'
silicon or a silicon alloy, but lie badllneeds a11 indication to tell him when he has added sufficient silicon. In today's rxpid electric furnace melting. some rapid means for measuring the redox poteiitisl of the molten slag and, thus. tlie end point of the titration, would revolutionize alloy steel protluction. I t is not an easy problem, but such a device would be as valuable to the metallurgist as the p H meter has been to the chemist. Likewise, tapped nietal is still reacting in the ladle and continues to react nith ladle refractories. Presentday spectrographic analyses are ver!. fast compared to anything known when the ;In.ard winner started in analytical chemistry, but still the metallurgist must wait for analyses. A means of analyzing niolten metal would gire him a n opportunity to improve his product materially and prevent many scrapped heats. Ideally, such a device THE FUTURE should monitor the metal stream as infrared devices are used t o monitor Progress in analytical chemistry has organic streams. Perhaps a future alrvag-s been in the direction of norking Fisher -In.ard will be for a waterwith smaller and smaller samples. cooled x-ray spectrometer or similar Where the chemist used 5 to 10 grams device. a century ago, we niay use 50 nig. toYacuum technology \Till expand in day, but commercial alloys are not metallurgy, and here the need for a homogeneous. so in the future more device to aiialyze metal while it is in :I thought must be given to w y s of vacuum chaniber is very great. Onl!. securing samples that truly represent historical annlj-ses can be provided at the material under examination. Much present 011 vacuum-produced heats. progress has Iieen made in statistical arch analysis of metals, methods in the four decades the .%\yard in man>-cases: it is no longer sufficient \rinner hns been working in analytical to estimate the weight per cent of an chemistry, but sampling is a nrglected elenient prcsent. The compounds presarea. Much hettcr sampling techniques ent and their states of aggregation should be developed. Some niay come rather than the simple weight per cent of from the use of w r y rapid methods for elements determine t,he properties of estimating tlic coniposit'ion of many materials. Some work has been reparts of the sample and intrgrating the ported on conipound extraction and results. Rapid instrumental methods estimation. The excellent paper of based on solid saniples enable t'he Beeghley ( 1 ) 011 the aluminum-nitrogen chemist to integrat'e analyses rather conipounds present in steel is an exthan to composite samples to achieve ample of this type of analysis. Tlicrc. the same result,. Still the results arrive is a deniarid for more n.ork in this too slowly for even present-day pracarea, so that we can secure a bettor tices. understanding of the factors that Metallurgical furnace practice is degovern and control the grontli of termined to a larger extent than most structures in metals and alloys. I k metallurgists will admit 1)). the availcause there are no metals preselit in the nbilit>-(or nonnvailahilitj~jof analytical earth's crust that have not been tried in control. If fastclr rnctliocis of anal!-eis steel, the only hope of improving steels could be niatle nvai1:il)lc. optimum furnace practice. in many,cs~es. ~ o u l d is to lwrn hoiv to put them t o g p t h hrtter. Here the role of the analytical hear littlr rcsembl:~nce to that used chemist is to devise new methods for todaJ-. This is i m n e out hy the big vhanges direct-reading sp~ctrographs cstiniating inorganic compounds similar to the functional group analyses that i m r e made possihle in sterl production. have hcen so useful in organic analysis. One of the present nicthods for I s the mctal industries have becomr niaking st:iiiilrss steel involws nic,lting more scicntific, a greater hurdm is htainless scrap, tlien bloi~ing with placed on the analytical cheniist t o oxygen until the carbon is reduced to a help answer the question, "IVhj. (lo very lon, value (
