1320
ANALYTICAL CHEMISTRY
Procedure. One drop of the acetic acid solution to be tested is treated in a micro test tube with 1 drop of reagent solution. The sample may be the free base or the hydrochloride. The mixture is warmed in the water bath for 1 to 2 minutes. Depending on the quantity of 1-naphthylamine present, a more or less intense violet coloration develops. A blank is advisable when only slight amounts of 1-naphthylamine are involved. Identification limit is 0.5 of 1-naphthylamine. Dilution limit is 1 to 100,000, The test for antipyrine described here seems to be a Qpecial case of a general method for detecting aromatic compounds which yield true C-nitroso derivatives. This follows from the behavior of aniline, diethyl-, and dimethylaniline, phenol, and also 1- and 2-naphthol, Only the first four of these compounds give a distinct violet or brown color after they have been nitrosated, the excess nitrous acid has been removed, and then they have been heated for some time n ith I-naphthylamine. The naphthols yield
no more than a faint color and even this result is probably due to the fact that t.he nitrosonaphthols are not true C-nitroso compounds but instead are, to a large extent, the isomeric quinosiiies. ACKNOWLEDGMENT
The authors gratefully acknowledge the support of this work by the Conselho de Pesquisas. LITERATURE CITED
(1) Knorr, L., Rer.,'17, 2083 (1884).
( 2 ) S h c h e z , J. A,, "Curso de Quimica Analitica Funclonal de lledicamentos Organicos," Vol. 11, 2nd ed., Buenos Aires, 1947. (3) Sommer, F., and Pincus, H.. Ber., 48, 1963 (1915). (4) Wagner, R. B.. and Zook. H. D., "Synthetic Organic Chemistry," p. 1765, Wiley. Kern York, 1953. RECEIVEDfor review February 16, 1955.
Accepted H a y 2 , 1955
Microreflectivity Analysis of Coal J. T. MCCARTNEY, Coal Constitution and Miscellaneous Analysis Section, Bureau o f Mines, Pittsburgh, Pa.
L. J. E. HOFER, Synthetic Fuels Research Branch, Bureau of Mines, Bruceton, Pa. .i proposed objective method of petrographic analysis of coal based on variations in reflectivity of the coal components has been tested. The analysis is made on polished solid blocks or briquets of granular samples, using a specimen scanning device, a reflected light microscope with high resolution of areas of different reflectivity, a photomultiplier photometer, and a recording microammeter. Comparison of results by this method with those of the Bureau of Mines thinsection technique shows that the former can evaluate, probably more objectively than the latter, the proportions of the opaque components that arc relatively resistant to hydrogenation and usually have weak coking properties. Thus this new method should be of value in the selection of coals suitable for hydrogenation to gasoline and coal chemicals, and in the control of blending practices for coal carbonization.
P
ETROGRAPHIC analysis of coal usuallv has been made either on thin sections by transmitted light or on polished surfaces by reflected light. The former method has been favored in the United States, pal ticularly b>- the Bureau of Mines (IO), while the latter has been developed chiefly by German coal petrographers (6). Each has its advantages and disadvantages. The thin-section technique is characterized by striking color differences that are of great value in differentiating various coal components; the polished surface method is favored because of easier specimen preparation and better differentiation of constituents that are opaque in thin section. The German coal petrographers apparently make little use of quantitative reflectivity measurements in their routine anal) ses, but rely mainly on qualitative estimations of degrees of brightness, together mith structural variations to classify the different coal components. Quantitative determinations of coal reflectivity received great impetus from the startling assertions of Seyler (12, IS), who contended that the reflectivities of the woody constituents of all coals were tightly grouped in a discontinuous series and that variations in reflectivity caused either by diagenetic differences or metamorphic changes always occurred in definite steps. Although studies by the Bureau of Mines (9) failed to substantiate Seyler's claims. quantitative measurements of the reflectivities of coal components should have considerable value in improving and supplementing the present methods of petrographic analysis.
Inadequacy of the thin-section method r a s emphasized by a Bureau of Mines investigation of the value of petrographjc analysis in predicting the probable yields of liquid products in the hydrogenation of cool to synthetic fuels and gasoline ( 4 ) . This study showed that there was a rough correlation between the yield of insoluble residue resulting from hydrogenation and the amount of relatively inert components, opaque matter, and fusain! in the original coal. However, in different' coals, the proportions of opaque matter that could be liquefied were found to vary from 40 to SO%, and 10 to 55% of different, fusains liquefied. The varying resistance to liquefaction probably depended on the effective rank of the opaque constituents, but no accurate method of determining this \vas known. However, the degree of opacity was an important factor in determining resistance to hydrogenation and a method for measuring such variations would have considerable value. Unfortunat,ely, the difficulties involved in controlling the thickness of various areas of extremely thin coal sections discouraged attempts to proceed along this line. Because the reflectivities of coal components are approximately inversely proportional to their translucences in thin section, the possibility of developing a method of petrographic analysis based solely on quantitative mcasurenients of reflectivity was explored. Seyler has published some results of this type (II), showing the proport,ions of coal samples having reflectivities equivalent to several of the steps of his series. His analyses a e r e made on both solid blocks of coal and granular samples molded into a briquet with a binder. Seyler measured the reflectivity visually with a photometer attached to a microscope and totaled the amounts of each component x i t h a manually operated integrating stage. This appears to be an extremely laborious and time-consuming procedure. The possibility of utilizing a photoelectric detector, together r i t h a recorder, t o measure reflectivity variations in a coal sample on a moving microscope stage seemed promising, and n-ith this objective the present investigation -+vas undertaken. EXPERIMENTAL PROCEDURE
Description of Coal Samples. Descriptions and analyses of coal samples similar to those used in this investigation are shown in Table I. These analyses do not apply strictly to the specimens studied because in most cases these were selected small portions from different locations in the coal beds. The data are given t o show the general nature and rank of the specimens. Preparation of Coal Specimens. Because it is advantageous to be able to make petrographic analyses on small granular samples representative of large lots of broken coal. a technique
V O L U M E 22, NO. 8, A U G U S T 1 9 5 5
1321
was developed for binding such samples into a briquet suitable
.
.sx.
"
- "-..("."
T*
sized coal, agd excessive proportibns of fine particles in samges crushed to smaller top sizes. The coal should he crushed so RS and waxes were tried.
I t s index of refraction is such t h a t t h e
dye, nigrosine, is disueked in the resin.
."
T& Sa&o!ite is also
. . Figure 2.
Miororefleetivity apparatus
wheel to ensure uniform distribution of coal and hinder CSX
A fresh flat surface is exobsed on t h e 6 r i q u e t by grinding on
ing powdkr. TI& bFiquets polish ;ell, the binder heioming fairly uniformly hleck and the coal particles reasonably free from scratches. Solid pieces of coal are ground and polished in the same manner. Method of Analysis. Figure 1 shows a schematic diagram of the npparatus used in obtaining reflectivity distribution curves
ently unavoidable loss of sensitivity occurs owing to fatigue of the photomultiplier tube. A correction is applied to the test record, assuming t h a t lass of response is linear with time. The chart is analyzed by measuring manually with B map measure the lengths of the regular chart graduations t h a t lie below the curve. Because each line represents a fixed value of refiectivitv
Che results are correct,ed ta-represent only the coal in thk briquet;
plotted. Coal reflect,ivities are measured in cedar oil hecause the con-
flexible cable attached to the nne-pitched stage screw an4 driver
.~~ strains in the stage that dikurh t h e focus on t h e surface.' ~
~~~
~
comuonents are increased, thus d i n g in differentia,tian. T h e
Y
Light from a 6-volt, 5-rtmpere, tungsten-filament lamp, kepi constant by a storage battery whose output is balanced by a re@. lated charging current, is led through a vertical illuminator and reflected from the specimen surface up through a '/Anoh oi: immersion objective t h s t forms an image of the surface a t thc microscope ocular. I n this plane is placed a very fine resolving pinhole, which has an effective diameter of 1.85 microns a t the specimen. Thus a circular area of this diameter is exposed to the photomultiplier detector fastened above the ocular. The output of the photomultiplier is fed through an amplifier to B Speedomax recorder, which balances and records full-scale deflections in 1 second. As t h e specimen moves a t a rate displacing the exposedI area its own diameter in the 1 second necessary to record a CUNC is drawn on the recorder chart of the variations in reflec)tivity 01 the specimen surface. Figure 3 shows 8 sample test record representing about 0.4 mm. of the traverse. At intervals of ahoul 20 minutes during the test, the specimen is ahserved visually through the side observation tube shown and slight variationa from focus are corrected. The Eero setting of the photometer amplifier, which drifts slightly, is also adjusted a t this time, A te& requires about 3.5 hours. The chart is calibrated by recording the reading on a polishedI surface of calcium timgstate, whose reflectivity is similar to that of coal. This is done before and after a test, because an appar-
Figure 1. Schematic diagram of equipment for microreflectivity analysis of coal
partides and on finely divided attrital matter. I
I ~ , .
~
~
~
~
the^ photomultiplier
~~
~~
~
The values of
I
~
~~
~~~
photometer a t maximum sensitivity. Thg output of the photomultiplier tube, after nine stages of nmplifieation within the tube, is of the order of 10-Qampere.
7-I
I
Many 01 uit: mea,ure~~muw I I I Y U I Y ~ UIU MLIC y~v~'ouurn XB ILB~LT the limits of performance of available instruments. The size of the resolving aperture was chosen such t h a t the reading of the photometer meter on the most sensitive range was full scale for the calcium tungstate reflectivity standard. Thus the resolution a t the specimen, 1.85 microns, is limited b y the sensitivity of the photomultiplier. By using a more intense light source or a more efficient condenser, this resolution might he improved, hut in any case the limit of resolution of this optical microscopic sys-
ANALYTICAL CHEMISTRY
1322
Figure 4.
Figure 5 ,
Reflectivity distribution curves
Duplicate briquetted samples of granular coal from bright and splint layers of Alma high-volatile A coal
Reflectivity distribution curves
Solid blocks a n d granules from two coals of different type
100
3 d Q
z
0
1
5
s
75
r I r L
z Y
-
50
>
r 5
8 L
cc
I
3
>
5
-"
25
L
0
z
Y
J
c
5
1
15
2
REFLECTIVITY P E R C E N T
Figure 6.
Reflectivity distribution curves
Figure 7.
Reflectivity distribution curves
Solid blocks and granules from bright and splint layers of 41ma highvolatile A coal
Adjacent solid blocks from bright and splint layers of Alma highvolatile A coal
tem, about 0.5 micron, prevents improvement beyond that point. Because mechanical scanning of a somewhat uneven specimen surface is involved, resulting in uncertainty of focus, the maximum resolution of t h e microscope under these conditions is probablynot much better than 1 micron. Improved light sources, microscope objectives with higher numerical aperture, more sensitive photometers, or more even specimens can under no circumstances improve the resolution of t h e measurements by more than a factor of 4 and probably b y not more than 2 . The speed of scanning is given by t h e scanning area diameter, 1.85 microns, divided b y the response time of the recorder, 1 second, or 1.85 microns per second. This scanning speed is therefore limited by the recorder response time, which for the fastest potentiometer-type recorders is nom about 1 second. Direct-recording galvanometer types are faster but correspondingly less acciirate. h major improvement could be gained by substituting electronic integrating circuits for t h e relatively
s l o w l ~responding potentiometer recorder. By the use of counters or timers that Tvould start and stop a t certain values of reflectivity, the test time could be greatly reduced and mechanical analr-sis of a chart eliminated. T h e length of scan is tnben as about 100 times the diameter of the largest particle in a granular specimen. This is done so that thc scan n ill be subject to statistical fluctuations of not more than 1%. T h e number of scans necessary for any desired accuracy depends on the representativeness of the sample, the homogeneity of the briquet, and the qiiality of the polish. T h e error resulting when the particles being scanned are not much larger than the scanning area causes a false contour of t h e recorded reflectivity curves, which may be described in a simplified wdy. If a scanning area of diameter A microns is used to scan a particle D microns in diameter, the particle will appear to be larger in diameter bv A microns and it \vi11 register its true reflectivity for a distance of A microns less than the true diameter of
.
V O L U M E 27, N O . 8, A U G U S T 1 9 5 5
1323
Table 1. Description and Analyses of C o a l Samples Coal Bed
... A To. 6 So.
5
America
.41ma Layer Layer
...
Hillman
Mine
Proximate Analysis, % Volatile Fixed matter Carbon
County
State Rank Moisture , . . .,. Alberta,. Lignite 13.1 Can. WiseHill Moffat Colo. Subbituminous 13.4 No. 2 A Old Ben Franklin Ill. High-volatile 10.3 No. 15 bituminous B Thermond Gallatin Ill. High-volatile 1.6 bituminous A America Walker Ala. High-volatile 2.6 No. 3 bituminous .i Red Jacket Llingo W. Va. High-volatile No. 6 bituminous A 2 (splint) 1 1 3 (mixed bright and splint) 1.2 ... ... Alberta, Low-volatile 0.6 Can. bituminous Henry Luzerne Pa. Anthracite 4.0
Ultimate Analysis, Yo Nitrogen Oxygen Sulfur ~
Ash
Hydrogen
Carbon
calorific Value. B.t.u.
38.0
42.5
6.4
5.1
56.3
1.2
30.5
0.5
...
30.8
46.9
8.9
5.5
60.2
1.2
23.5
0.7
10,470
33.6
48.6
7,s
5.4
67.3
1.5
17.0
1.3
11,900
37.3
51.8
9.3
5.2
73.4
1.5
7.3
3.3
13.260
31.0
49.8
16.6
4.7
67.1
1.5
8,4
1.7
12.070
39.2 36.4 16.5
57.0 59.2 78.0
2.7
5.4 5.4 4.4
83.1 82.1 84.6
1 3 1.5 1.3
5 9 5,9 4.3
0.2 0.i 0.5
14,930 14,890
4.9
5.7
85,s
4.5
3.0
85.9
0.9
5.1
O.G
13,880
.
the particle. T h e total error on the complete record will be larger v-ith greater proportions of fine particles. RESULTS
Duplicability. The reproducibility of results from this type of test was first determined for two adjacent 20-mm. traverses on the same briquet. Reflectivity distribution curves for two traverses on a briquet of selected anthraxylon (vitrain) from a highvolatile €3 coal from the No. 6 bed of Illinois showed an average difference of 1%. A difference of 37' \vas found for t x o traverses on a briquet of splint coal from the America bed of Alabama. This appears to be very satisfactory reproducibility on the same specimen, and the deviation is understandably much less for the uniform anthraxylon than for the heterogeneous splint, coal. The duplicability for traverses on two different briquets is shovn in Figure 1 for crushed samples from bright and splint layers of .Uma-bed high-volatile A coal from K e s t Virginia. Here are introduced the additional possible differences of sampling and polishing in the two briquets. The agreement is still good, the average difference for both the bright and splint-coal briquets being about GYo. This order of rep:oducibility for single traverses o q two different briquets is reasonable. Of course, a statistical stud)- should be made of results for a number of traverses on briquets containing coals of different ranks and t>-pes to determine the number of traverses required for a given allowable tleviation. There is little or nothing in the literature describing the application of lineal analysis to specimecs of this type. Comparison of Results on Briquets and Solid Blocks. Comparative results on solid pieces of coal and briquets of granular (minus S o . TO-sieve) coal from adjacent locations in the bed $how the effects of possible errors inherent in the analysis of granular c o d . Figure 5 s h o w such reflectivity-distribution curves for Illinois S o . 6-bed high-volatile B anthraxylon, the hlocks and granules of which are f:iirlJ- homogeneous. and for an .\merica high-volatile A attrital sample, vihich consists of verjfinelj- disseminated coal material. The curves for the solid and granular anthraxylon are rensonably similar through most of the range but with marked deviation of the upper portion of the granular cos1 curve towtrd Ion-er reflectivity values. This is probably caused by the previously described edge effects between dark hinder and brighter coal. The difference betn-ten the wflectivity distributions of the solid and granular attrital coal is much less than for the anthraxvlon, possibly because insufficient resolution of very fine detail in the coal itself, both in solid and granules, masks the effect of discontinuity i n the granular coal. Figure 6 s h o w a similar comparison for bright and splint l : t ~ - efrom ~ s the same bed of Alma high-volatile A coal. Here the differences between solid and granular samples appear to be greater, even though thtvx curves represent the averages of traverses on two different blocks or briquets, Tvhile those in Figure 5 are for single tests. I n both these samples of Figure 6, the structural details are larger than in the spliiit simple of
3.2
...
Figure 5 , so that resolution is better for both blocks and granules, and the difference must be caused mostly by particle resolution rather than structural detail resolution. I t is also possible that the block and granule samples are riot quite the same, since they come from different, t,hough adjacent. locations. The curves for the ant,hrasylon of Figure 5 may be closer because it does not all have the same reflectivity. and the selected solid piece may have a lower than average reflectivitJ-. as is indicated by the granular curve showing high reflectivity near the base of the graph. The average order of agreement betmeii d i d and granular coal is probably better represented by Figure 6. The differences are appreciable, but the changes in the distributions are puallel. Therefore, although the results on granular co:il are lower than the true values, the errors on most coals should be reasonably comparable and the great advan tage of analvziiig small granular samples over large columns of solid coal may outweigh the errors involved. Figure i shows a comlxriison of reftectivitJ-tlistiibution curves for traverses on two b1ocl.s of solid coal selected from adjacent locations in the same layer. The cliatrihutiom for the traverses on the splint coal agree closely, p: obably because the a~er:cgedistribution of the finely divided attritus does not vary much within the same layer. The bright-coal distributions deviate more, probably because there is more chance of variation, since some rehtively large anthrasylon bands may not be continuous over appreciable distances. Actually the txr-0 bright-coal traverses x-ere made about I/. inch apart on the same block, but there F a s an evident anthrasylon band about l,'J inch n-ide that was crossed by only one of the trave s. In general, two traveises on adjacent solid-coal pieces would be expected to vary more than those on tn.0 briquets of the same sample of granular coal. The possibility of preparing briquets of granular coal by means of high pressures without the use of binder as investigated. Briquets of minus S o . 200-sieve coals of different types were prepared a t 200,000 pouiids per square inch. -1good polish on these briquets was difficult to obtain! and the high pressure apparently caused excessive alteration of structural details. A trial test on one of these briquets gave a reflectivity-distribution curve that had :I loiver average reflectivity than that of a minus No. 200sieve briquet' n-ith binder. It n-as tentatively concluded t h a t such high pressure briquets Rould be unsuitable for these reflectivity studies. Effect of Rank of Coal. Previous investigator2 have shown that the reflectivity of anthrasylon or vitrain varies more or less regu]ail>- with rank ( 6 ) . Figure 8 shows reflectivity distribution curves for coals ranging in rank from lignite to nrlthracite. The upper parts of the curvefi for anthracite and low-volatile bituminous coal are apparently in error because of insufficient resolution on fine particles and the relatively large difference between the reflectivities of the coal and binder. Coals of high-volatile A rank and lo~vcrappear to be less seriously affected by this error. The coal samples represented are riot strictly comparable by type,
1324 for some are bright coals and others are splint or semisplint coals. The average 1 eflectivitics increase with rank, but there is considerable overlapping. The high-volatile h samples contain some coniponents of higher reflectivity than much of the low-volatile coal, and the subbituminous sample has components of greater reflectivity than some in the high-volatile coals.
Figure 8. Distribution of components of varying reflectivity in coals of different rank
A complicating factor in studies of reflectivity of coal arises with the appearance of anisot,ropy in higher rank coals. Cannon and George ( 1 ) found evidence of anisotropy in a coal of 25% volatile matter, b u t it did not seem appreciable in coals below semian thracitic rank. Dahme and 3Iackowsky ( g ) classified coals with 10 to 18% volatile matter as weakly anisotropic and those b e h v 10% as strongly anisotropic. Van Ilrerelen ( 7 ) stated that coal is anisot'ropic a t a carbon content above 87%? h u t his data do not s h o v appreciable anisotropy below about 91 % carbon. .Ipparently anisotropy becomes marked only in the anthracitic coals! hut may he slight'ly evident in coals of Ion-and medium-volatile rank. This phenomenon is probably of little importance for most granular samples that would be treated by the type of measurement described here, but t,he possible variations of reflectivity in different directions Tvith the bedding planes should be consitlewd in most discussions of coal reflectivity. Effect of Type of Coal. The efficacy of this method of analysis in distinguishing between different types of coal is of great interest. Figures 4 to 7 offer evidence on this point. Figures 4, 6, and 7 shoil- the differences between reflectivity distribution curves for samples of bright, and splint coal from the same bed. The splint coal obviously contains a large proportion of components with greater reflectivit>- than those of the bright coal. This agrees with the conception that opaque constituents that are more abundant in the splints have higher reflectivities than the more translucent, components of the bright coals. T o compare the results by this method more accurately Kith those obtained in the standard Bureau of Mines thin-section analysis, the solid blocks on which reflectivity data were obtained were subsequently used t o prepare thin sections, and t,ransects were made along approximately the same 20-mm. lengths as vere traversed in the reflected light studies. The data obtained t,herehy are tabulated in Figure 7 . The greatest differences hetv-een the bright and splint, samples lie in their contents of opaque attritus. More
ANALYTICAL CHEMISTRY than 40y0 of the splint coals but only lOy0 of the bright pieces useful criterion for assessing consist of opaque constituents. the meaning of t'he reflectivit y-distribution curves as related to translucence might lie in thc average reflectivity of the main anthraxylon component of the coal. For the .Ilma high-volatile A coal this was determined on relatively wide uniform bands of anthraxylon and found to be approximatell- 0.88%. Inspection s h o w that) about 44yo of the components in the solid splint-coal samples have reflectivities higher than that of the major anthraxylon component, vhile about 4 to 11% of the bright samples have higher reflectivities. It is undoubtedly somewhat fortuitous that these figures agree so m l l with the opaque-matter contents determined by thin-section analysis, but this appears to be x useful niethod of interpretation. Figure 5 also shows the differences hetm-een tn-o coal samples of different type. The Illinois anthraxylon has nearly uniform reflectivity throughout, rvhile the sample of Alabama attrital coal selected from a splint layer has components of a v-ide range of reflectivitJ-. Spores or e:\inite in this sample have low reflectivity and opaque matter has high reflectivity. A source of error that has not been mentioned is the presence of mineral matter in t,he coal. Its reflectivity is usually high, but it would he difficult to recognize and subtract its contribution t o the reflectivitj- record. I t probably nould be desirable to remove a good deal of the mineral matter from the granular sample hy gravity separation methods. However, if the mineral content is not excessive, not over 10% by weight, its contribution to the reflectivity analysis based on volume per cent T o d d be usually less t,hm 4% and differencrs hetneen most coals would be much less than this. Possible Applications of Results. The most obvious application of results obtained by this method of analysis appears to lie in prediction of the amenability of coals to hydrogenation into liquid fuels. As previously discussed, the constituents most resistant to liquefaction are those that are opaque in thin section and have relatively high reflectivities. The quantities obtainable from the reflectivity distribution curves that might be t,ried for correlation ivith yirlds of insoluble residues in hydrogenation tests are the proportions of the coals having i,eflectivities greater than their main anthrasylon component, the proportions with reflectivities greater t h a n a fixed value, and the relative distribution of these higher reflectivity components. T o illustrate the latter. the curves for the two high-volatile bituminous coals in Figure 8 are of interest. The Alma and Xnierica coals have about the same proportions of constituents with reflectivities greater than t,hat of the anthraxg-lon, which is about, 0.88% in both coals. Hoiyevcr. the America coal has greater amounts of higher reflective components-for instance, 12% of the -1merica coal has reflectivit'y above 1.40%, while only 6y0 of the Alma coal has this reflectivity, 2nd this contrast continues to higher reflectivity values. Characteristics such as these may be found to have valuable application to prediction of hydrogenation yields. The potential usefulness of the Bureau of Mines t,hin-section technique i n assaying coals proposed for hj-drogenation has been discussed. This neiv reflectivity method. besides being more objective. apparently can characterize more critically the opaque conipoiierits that are difficult to liquefy. To further explore the value of this method, a program of tests should he conducted to determine the possible correlations with the yields obtained in small scale hydrogenation tests. If a good and useful relationship can be demonstrated. this analytical method mould offer a simple, inexpensive means of determining the relative merits of different coals that are economically available for the production of gasoline and coal chemicals by hydrogenation. This more objective met,hod of actually measuring the reflectivity variations in a coal sample should also be of value in supplementing the reflect,ed-light methods of petrographic analysis that are favored by European investigators and are currently attrarting attention in this country. German petrographers, in
1325
V O L U M E 27, NO. 8, A U G U S T 1 9 5 5 particular, are making extensive use of these techniques in controlling the blending of coals for the manufacture of metallurgical coke. Van Krevelen (8)in T h e Netherlands has recently proposed a simplified form of presentation of the results of petrographic coal analysis t h a t he believes has considerable practical value t o t,hose concerned ivith problems of preparing coals and blends for carbonization. Van Krevelen would report an analysis with figures such as these: 5-721, where the number 5 represents the reflectivity or rank of tho vitrinite (anthraxylon) in the coal on a scale of 0 t o 9 similar to Seyler’sst,eps,and t,he figures 721 represent 70% vitrinite, 20% esinite (spores), and 10% inertiriite (opaque matter) as the petrographic composition of the coal. Because the exinite is of lowest reflectivity, the vitrinite intermediate, and the inertinite of highest reflectivity, the reflectivity distribution curves obtained by the method presented here should be amenable to an interpretation that will furnish data similar to that proposed by I-nn Krevelen. LITERATURE CITED
(1) Cannon, C. G.. and George, R’.H., “The Ultra-Fine Structure of Coals and Cokes,” p. 290, British Coal Utilization Re-
search Association, London, 1944. (2) Dahme. A , , and 3lackoB-sky, M,-Th.,Brennsto.#--Chern,, 32, 175 (1951).
(3) Fieldner, A. C., and Selvig, W. ri., U. S. Bur. Mines, Bull. 492 (1951). (4) Fisher, C . H., Sprunk, G . C., Eisner, il., O’Donnell, H. J., Clarke, L., and Storch, H. H., U. S. Bur. Mines, Tech. Paper 642 (1942). (5) Freund, Hugo, ”Handbuch der Mikroskopie in der Technik; Band 11: Mikroskopie der Bodenschitee; Teil I : Mikroskopie der Steinkohle, des Kokses, und der Braunkohle,” Umschau Verlag, Frankfurt am Main, 1952. (6) Hoffman, E., and Jenkner, A , , Gliickauf, 68, 81 (1932); Fuel, 12, 98 (1933). (7) Krevelen, D. TI’. van, Brennsto$-Cheni,, 34, 167 (1953). (8) Krevelen, D. W . , van, “Representation of the Quantitative Petrographic Analysis by Means of a Decimal Code,” Central Laboratory, Staatsmijnen in Limburg, Geleen, Holland, 1953. (9) McCartney, J. T., Econ. Geol., 47, 202 (1952). (10) Parks, B. C., and O’Donnell, H. J., Am. Inst. Mining Met. Engrs., Tech. Publ. S o . 2492; Transactions, Coal Div., 177, 535 (1948); Coal Technol., 3 (1948). (11) Seyler, C.A., Fuel, 28, 121 (1949). (12) I b i d . , 31, 159 (1952). (13) Seyler, C. A . , Proc. S . Wales Ins!. E n g r s . , 63, 213 (1948). (14) Stach, E.. Gliickau;, 73, 330 (1937). RECEIVED for review August 18, 1954. .iccepted .Ipril 4, 195.5. Presented before the Division of Gas and Fuel Chemistry a t the 126th Meeting of the h f E R I C A X C H E Y I C . 4 L S O C I E T Y , New T o r k , s.Y . , September 1954.
Field Determination of Microgram Quantities of Niobium in Rocks F. N. WARD
and A. P. MARRANZINO
U. S. Geological Survey, Denver Federal Center, Denver, Colo. A rapid, simple, and moderately accurate method was needed for the determination of traces of niobium in rocks. The method developed is based on the reaction of niobium(\’) with thiocyanate ion in a 451 hydrochloric acid and 0.5M tartaric acid medium, after which the complex is extracted with ethyl ether. The proposed procedure is applicable to rocks containing from 50 to 2000 p.p.m. of niobium, and, with modifications, can be used on rocks containing larger amounts. Five determinations on two rocks containing 100 p.p.m. or less of niobium agree within 5 p.p.m. of the mean, and the confidence limits at the 95% level are, respectively, =t6 and A4 p.p.m. The addition of acetone to the ether extract of the niobium thiocyanate inhibits the polymerization of the thiocj anate ion and stabilizes the solution for at least 20 hours. The proposed procedure permits the determination of 20 y of niobium in the presence of 1000 y of iron, titanium, or uranium; 500 y of tanadium; or 100 y of tungsten or mol?bdenum or both.
A
S P a R T of its contiibution to a commodity stud? of certain strategic materials, the U. S. Geological Survey is develop-
ing geological information concerning the element niobium. This progi am required a field screening of potential niobium-bearing materials, in order t o eliminate shipment of barren samples to the laboratory and t o permit the field geologista to make appropriate adjustments in their exploration program v-ith miniinurn delay A rapid eemiquantitative method for determining traces of niobium in rocks was needed for this screening operation. Until recently the determination of traces of niobium by chemical methods was unsatisfactory because the available reactions were not sufficiently sensitive, and the niobium had to be separated from numerous intei fering elements such as tantalum, vanadium, uranium, molybdenum, and tungsten. Often these separations were incomplete. Chromatographic proceduies (8),which offer a slightly different approach, are now used to separate niobium
from some of the interferences and t o concentrate it on a suitable absorbent. The niobium can then be estimated by a colorimetric method based on the reaction of niobium either with hydrogen peroxide in strong sulfuric acid ( 9 , 13) or with pyrogallol in alkaline medium ( 7 ) . More than 50 years ago Pennington (12) observed qualitatively that niobium formed a yellow color with thiocyanate in an acid medium. Since then several workeIs (1, S, 1 0 ) have made significant contributions to better methods of determining niobium with thiocyanate. Freund and Levitt (3)studied the effects of different concentrations of acid, stannous chloride, and thiocyanate on the reaction in an acidic-acetone-water mixture. 1,auwZecha, Lord, and Hume ( 1 0 ) made a similar study using ethyl ether to extract the niobium thiocyanate from the aqueous solution. Alarzys (11) applied the reaction to the determination of small amounts of niobium in lov-grade ores and minerals and studied the relative merite of the n-ater-acetone mixture and ether as solvents of the niobium complex. He made involved separations of copper, mercury, platinuni, arid molybdenum, and concluded that classical method. must br used to determine niobium in the presence of vanadium The method here presented contains no involved separations and is not subject t o intrrference from vanadiuni, titanium, or tantalum. EXPERIJI ENTAL
Stability of Niobium Thiocyanate in Ethyl Ether-Acetone. The apparent instability of the yellow-colored niobium thiocyanate in ethyl ether is a serious drawback to methods that use the ether extraction t o increase the sensitivity and make the reaction more specific. The term “instability” is here used cautiously, because the evidence of such is indirect and no one has demonstrated that the niobium complex changes in any manner. Freund and Levitt (3)observed that during a given time the total absorbance of an acid solution of niobium thiocyanate remained constant, but the absorbance of the blank increased. Lauw-Zecha, Lord, and Hume ( I O ) observed that the intensity of
