524
INDUSTRIAL AND ENGINEERING CHEMISTRY
curacy which includes this factor was undertaken. To six of the fertilizer samples selected at random, definite amounts of boron, manganese, and copper were added and the samples were reanalyzed. The results and comparisons are shown in Table 111. COhlPARISOPi WITH CHEhfICAL RESULT^. A comparison Of the average of the spectrochemical determinations with the chemical results obtained by Lundstrom and Mehring (3) are included in Table I. Khile in a few cases the ratios of the chemical to the spectrochemical values vary appreciably from unity, in general these ratios are within a twofold variation. There is no significant trend in the comparison of the two methods, although the spectrochemical results for boron and manganese tend to be somewhat higher than the chemical, while the opposite is true of copper. Study to determine a possible cause for the discrepancy between the two methods has not been attempted. Khen the difficulties encountered in the separation of these small amounts from the complex mixed fertilizers for their chemical determination are considered, a twofold variation is, perhaps, not surprising. The spectrograph provides a method whereby the usual analyses for the important primary plant nutrients in the fertilizer can be supplemented by a ready procedure for the determination of the secondary elements important to plant nutrition. Once the method described is established as a routine procedure, an individual could maintain an average of complete analysis of two or three photographic plates a day. This would involve the determination of three elements in from 14 to 21 samples, or from 42 to 63 determinations a day. Working curves permitting determination from a few parts per million to a few per cent could be established to correspond to the composition of the average fertilizer with supplemental working curves for the unusual samples-i. e., a fertilizer containing practically no lime. Upon the completion of the usual chemical analyses for the major constituents the spectrochemical analyst would have sufficient information for selecting the most appropriate working curve, and the deter-
Vol. 13, No. 8
mination of the concentration of essential secondary elements and the absence (above guaranteed values) of those elements producing toxic effects could rapidly follow.
Summary Using the low-voltage direct current arc and a method involving a step sector and internal standard, a procedure for the simultaneous determination of three of the more important secondary elements in mixed fertilizers, boron, manganese, and copper, has been found to give satisfactory results with an accuracy of about * 5 per cent. Study has shown that unavoidable background is the greatest single source of inaccuracy, and that preparation of base material to correspond to the average composition of fertilizers is satisfactory to avoid any error due to the effect of one ion on the excitation of another. The spectrochemical method can be used to supplement the chemical analysis of fertilizers for primary nutrients by providing B rapid method for guaranteeing the concentrat’ion of the essential trace elements. Literature Cited (1) Daniel, E . P., p. 213, Yearbook of E. S.Dept. Agr., 1939. (2) Gerlach, W., and Schweitzer, E., “Foundation and Methods of
Chemical Analysis by the Emission Spectrum” (authorized translation of “Die chemische Emissionspektralanalyse”, Vol. I, L. Voss), London, Adam Hilger, 1929. (3) Lundstrom, F. O., and Mehring, A. L.. IND.E s c . CHEM., 31, 354 (1939). (4) McMurtrey, J. E., Jr., and Robinson, W. O., p. 807, Yearbook of U. S. Dept. Agr., 1938. (5) Melvin, E . H., and O’Connor, R. T., “Proceedings of Seventh
Summer Conference on Spectroscopy and Its Application”, p. 42, New York, John W7iley& Sons, 1940.
(6) Myers, A. T.,and Brunstetter, €3. c., IXD.ENG. CHmr., Anal. Ed., 11, 218 (1939). (7) Scheibe, G., Z.angeu. Chem., 42, 1017 (1929). (8) Scheibe, G., and Neuhausser, A,, I b i d . , 41, 1218 (1928). (9) Scribner, B. F., Proceedings of Fifth Summer Conference on Spectroscopy and Its Application”, p. 51, New York. John Wiley & Sons, 1938.
Routine Determination of Phosphorus and Sulfur in Coke Catalytic Nitric-Perchloric Acid Digestion Method LOUIS SILVERRIAN, 5559 Hobart St., Pittsburgh, Penna.
W
ET oxidation of coal and coke to determine sulfur has been suggested (2, 11). This paper outlines a n analogous procedure for phosphorus and presents a modification of the Smith (11) procedure for sulfur in coke. Recent investigations of the structure of coke have shown that nitric acid oxidation converts a large percentage of coke into mellitic and oxalic acids ( 3 ) . As graphitic carbon is easily oxidized by perchloric acid when chromium and manganese are present, no difficulties should be encountered in the rapid oxidation of coke. I n the procedures described below phosphorus is considered present wholly as phosphate, while sulfur may occur as ferrous sulfide, sulfate, free adsorbed sulfur, and sulfur-carbon solid solution (7, 8 ) . The hazards involved are no greater than those encountered in the digestion of rubber or of cast iron. It is best to add nitric acid to coke first, to take care of any volatile matter.
Coke and perchloric acid should not be heated unless nitric acid is present.
Reagents Csed Zinc oxidenitric acid solution, prepared by adding 200 grams of sulfur-free zinc oxide to 1 liter of concentrated nitric acid. Catalyst. Equal weights of potassium permanganate and potassium dichromate, ground separately, and then mixed. Use about 60 mg. for each determination. Procedure for Phosphorus Keigh 1 gram of 60-mesh coke and about 60 mg. of catalyst. Transfer to a tall-form, narrow-mouthed 500-cc. Erlenmeyer flask, and cover with 20 cc. of fuming nitric acid (specilk gravity 1.5), 18 cc. of technical phosphorus-free perchloric acid (60 or 70 per cent grade), 1 drop of liquid bromine, and about 1 cc. of hydrofluoric acid. Place on a hot plate and boil gently for 10 minutes, then increase the heat to boil out the nitric acid and oxi-
August 15, 1941
dize the chromium to chromic acid (203" (2.). This should take not less than 45 minutes. Cool somewhat and add about 25 cc. of n-ater to dissolve the solid matter and 5 cc. of 3 per cent hydrogen peroxide. (The titanium content may be determined at this point, if required, 9.) Filter, wash with 1 per cent nitric acid, boil out the peroxide, adjust the acidity, and test for phosphorus (4). The following technique may be used: To the filtered solution add 6 cc. of nitric acid (specific gravity 1.42), boil out the peroxide, cool to room temperature, and dilute to 75 t o 100 cc. Add 10 grams of ammonium nitrate and 50 cc. of molybdate solution ($), stir well, and let settle. If the phosphorus content is low, estimate by comparison with a standard steel from nhich phosphorus has been precipitated at the same temperature as from the coke. Otherwiqe, filter and determine by the customary alkalimetric method. If the titanium content is over 0.3 per cent, add 2 cc. of hydrothloric acid (specific gravity 1.2), and allow the precipitate to settle overnight. TABLE I. DETERMISATION OF PHOSPHORUS Pioposed Method
w
0 012,0.012 0.012,0.012 0,024, 0,024 n 032~ 0 040, 0.042d 0.044
525
ANALYTICAL EDITION
Perchloric Acid lfethoda
?
:
Nitric-Hydrofluoric Acid Methodb c-
0 012
0 608 0.020 0 :&0d
...
0:Ok n. 032 0.040d 0.042
.ish 1 gram, add HF-HClOI, fume, and complete as usual b .Ish 1 gram, add HF-HSOa, evaporate, t a k e up u i t h H S O s , and complrtr a s usual C Manufacturers' result, 0 028 per cent d Titration by another analyst
Procedure for Sulfur \Yeigh 1 gram of 60-mesh coke and about 60 nig. of catalyst. Transfer to a tall-form narrow-mouthed 500-cc. Erlenmeyer flask, and cover with 10 cc. of the zinc oxide-nitric acid solution. Add 20 cc. of fuming nitric acid (specific gravity 1.5), 20 cc. of c. P. perchloric acid, 1 drop of liquid bromine, and about 1 cc. of hydrofluoric acid. Cover with a watch glass, place on a hot plate, and boil gently. After 10 minutes increase heat, boil out the nitric acid, and oxidize the chromium to chromic acid 203" C. This should t,ake not less than 45 minutes. ALTERXATEA. Remove watch glass, add 5 to 6 drops of concentrated hydrochloric acid from a dropping bottle, and repeat the additions of hydrochloric acid after the chromium has been reoxidized t o chromic acid, but remove the flask from the hot plate to prevent the remaining chromium from being reoxidized also (6).
ALTERSATEB. Remove the flask from the hot plate, add 2 cc.
of hydrochloric acid, reheat, and then cool somelvhat. Add about 25 cc. of water, heat to boiling, filter, and Tvash with hot water. Using methyl orange, neutralize the filtrate with ammonium hydroxide, and then make acid with hydrochloric acid, adding 2 cc. excess. Add about 0.25 gram of hydroxylamine hydrochloride to reduce iron and chromic acid, dilute to 200 cc., heat to boiling, and s l o ~ l yadd 10 cc. of a 10 per cent barium chloride solution, while stirring. Continue boiling gently until the solution has cleared and the sulfate has settled. St,ir in a little paper pulp. Filter through a Yo. 42 Whatman paper. Wash with hot barium chloride wash solution (6) (1 per cent hydrochloric acid and 0.1 per cent barium chloride). Finally, wash with water, burn, and weigh as usual.
Discussion The procedure is therefore: (1) oxidizing the carbon rings with fuming nitric acid, (2) dissolving the ash with hydrofluoric acid, (3) consuming the residual carbon with perchloric acid in the presence of the catalyst., and (4) preparing the resulting solut'ion for either phosphorus or sulfur precipitation. The range of phosphorus in the samples of coke available was from 0.01 to 0.04 per cent, and the range of sulfur was Sulfur was run by the Eschka from 0.5 to 1.0 per cent. method ( I ) and checked against the wet method (Table 11). I n Alternate B the conditions are those of the final steps in the determination of sulfur in steel (IO), while in Alternate A most of the chromium could be volatilized without loss of sulfur.
In determining phosphorus it is not necessary to volatilize the chromium or even to reduce from hexavalent to trivalent. When run side by side, the sulfur digestion is slower than the phosphorus, as only fuming nitric acid is used in the phosphorus determination while in the sulfur determination some nitric acid of 1.42 specific gravity is present. This indicates that the strong nitric acid is important and should not be boiled out too rapidly. Mechanical loss is also a t a minimum when digestion is not too rapid. Omitting hydrofluoric acid with cokes of 10 per cent ash gives low results for phosphorus and sulfur. Bromine is deemed essential with organic compounds containing sulfur, and the zinc compound retards volatilization of sulfuric acid if too much perchloric acid is inadvertently boiled out. The catalyst and the perchloric acid oxidize any remaining carbon, break up the ash, and indicate completeness of digestion. In Table I results obtained with the proposed method are compared with those employing dry-ashing for the rleterniination of phosphorus. I s compared with Smith's method for sulfur in coke ( I I ) , this modification probably owes its success to the use of fuming nitric acid, hydrofluoric acid, and bromine. Johnson, who based his sulfur method ( 2 ) on the permanganate oxidation of coke, used too small a sample (0.2 gram) and too much reagent ( 5 grams of permanganate, 50 cc. of nitric acid, 60 cc. of perchloric acid, and 50 cc. of hydrochloric acid). The proposed method gives the same precision of results as the Eschka method (Table 11), and is more rapid and easier to handle. Phosphorus and sulfur can be digested and later filtered side by side. Since the analyst need not wait for ashing before proceeding with the phosphorus analysis, both the phosphorus and sulfur determinations may be completed well within 5 to 6 hours. TABLE11. LschLa Method
DETERMISATIOS O F SULFUR
Alternate -4
Alternate B
7
0
0 . ,56 0 GD
0:88
0.70 0.75 0.T i 0.80
0.81 0.86
0 :S l
0.88 0.96
0 : SD 0.9ti
1.03
l'OG
0.58, 0.58 0.68 0.68 I). 75, 0 . 7 4 , 0 . i 4 0 . 7 4 , 0.73 0.81. 0 80, 0 . 8 0
n 79
o:si, 0.86
0.86
0.96
1.05,1 . 0 2 1.0s
Summary An improved procedure for the wet determination of sulfur in coke and a n original procedure for phosphorus are given, using the newer theories on the structure of coke as a basis for the method. The digestion acids are nitric and perchloric, not perchloric acid alone.
Literature Cited Am. SOC.Testing Materials, D271-37. Johnson, C. M., I r o n Age, 143, 33 (1939). Juettner, J. Am. Chem. Soc.. 59, 208, 238 (1937). Lundell et al.. "Chemical Analysis of Iron and Steel", p. 220, New York. John TViley 8- Sons, 1931. Ibid.,p. 237. Lundell and Hoffman, "Outlines of Chcniical Analysis", p. 47, New York, John Wiley & Sons. 1938. Powell, J. Am. Chem. SOC.,45, 1 (1923). Powell and Thompson, Carnegie Institute of Technology, Coal Mining Investigations, Bull. 7, 16 (1923). Silverman, Chemist-Analyst,23,4 (1934). Silverman, IND.ENG.CHEM.,Anal. Ed., 7, 205 (1936). Smith, G . F., and Deem, A. G., Zba'd., 4, 227 (1932).
