ANALYTICAL CHEMISTRY
288 generally applicable. It may also compensate for other possible interfering elements which were not studied in this paper. I n addition, by reading the perchlorate tilank separately one can obtain :in indication of the prpvnce of some unexpected element. CO3IPARISON
WITH
STANDARD COLORIRIETRIC
METHODS
The sulfate procedurps described lack the sensitivitj. of the thiocj-anate method, so that the latter ha‘ an advantage in the determination of estremrly small quantities of iron. The thiocyanate color lacks stability (8).Iionever, which should make the sulfate method more suitable for accuratt. work in anyt,hing but the lo\re,qt eoncentration rangt.. Thv inttlrference of cwpper in the thiocJ-mate procedure (8) appears to I)e grcater than irr the sulfate nirthod. The o-phenahthroline procedure is subject to many difficulties (8) from which the sulfate method is free. The former cannot be used in estremely acid solut>ions,nor in the presencc of a p p r c ciahle amounts of perchlorates. The itittxrference of man!‘ comnion metals is greater than in the sulfate method. An additional advantage of thc sulfate method over others is that it requires no special reagents. so that the solutions can be recowrcd and tested for other elements if desircd. OTHER METHODS
The procedures utilized abovc, 11y no means exhaust the iinalytical possibilities present in ferric pprchlorate and ferric sulfate solutions, if one is willing to isolate the iron. T o illustrate this, NBS sample 161 (0 34% C, 1.29% N n , 0.012% P, 0.005% S.
1.56y0Si, 0.04% Cu. 64.3% Xi, 16.9% Cr, 0.03% V, 0.005% Mo, 0.47% Co, 15.0% Fe) !\-as analyzed using sulfuric acid alone, the final concentration being 8 nil. per 100 ml. From a solution in which chromium was osidized, iron was isolated by a double precipitation with ammonium h3-droside. The precipitate x-as redissolved, taken t80sulfuric acid fume.;, and the solution trpated with a lit,tle hydrogen peroxide. Duplicate runs gave 15.0 and 15.1 % iron. It is possible that the ferric sulfate co:nples can be used to tleterniine larger amounts of iron accurately by differential or precision spectrophot,ometry. I n this work, however, the temperature sensitivity would be a very important consideration. LITERATURE CITED
.~braliAm. J., A c t a L i t . Sci. Regiae, VILZ‘U. H t c n ~ . FranciscoJ o s e p h i r m e , Sect. Chem., Mineral. P h y s . , 6 , 272 (1938). Glikman, T. S . , D a b , B. T a . , and Kutssya, B. F.,Zhur. Fiz. K h i m , 22, 906 (1948). Kiss, .i.,Aibrahbm,J., and Hepediis, I., Z . U ~ O T Q .allgem. Chem., 244,98 (1940). Iiiss. .$.. CsokBn, P., and S y i r i , G., 2 . p h y s i k . Chern., A190, 65 (1942). Olson, A. R., and Simonsoii. T. R., J . Chent. PhUR., 17, 348 (1949). Ibid., p. 1322. Rabinowitch, E., and Stockmeyer. IT. H., .J. A m Chern. .Soc.. 64, 335 (1942). Sandell, E. B., “Colorimetric Determination of Traces of Metals,” Chap. XXIII. Ken- Tork. Interscience Publishers, 1950.
RECEIVED for review J u n e 12, 1952. Accepted Koveniber 3, 1952. Presented a t t h e Pittsburgh conference on Analytical Chemistry and Applied Spectroscopy, Pittsburgh, Pa., March 1952.
Determination of Polythionic Acids KAYLMONDR . JAY Sinclair Research Laboratories, Inc., Harvey, 111.
Finely divided sulfur, useful for insecticidal purposes, is produced by the reaction of hydrogen sulfide and sulfur dioxide in aqueous solution. Because polythionic acids, formed as by-products, affect the particle size of the sulfur, it seemed desirable to develop a procedure for their determination. A n acidimetric method, based o n the reaction of the polythionates with mercuric chloride, gives check results with a deviation of less than 0.5y‘ from
LELIENTARY sulfur in a finely powdered form has found wide application in insecticidal sprays and as a fungicide. The reaction of hydrogen sulfide and sulfur dioxide in aqueous solution gives free sulfur in a very finelj divided state. However, the milky liquid, known as Wackenroder’s solution, resulting from this reaction also contains pol>thionic acids formed by side reactions. The polythionic acids present in JVackenr oder’s solution consist mainly of tetra- and pentathionic acids with traces of trithionic but no dithionic acids ( 3 ) . The presence of the polythionic acids seems to aid in heeping the elementary sulfur in a finely dispersed condition ( 1 ) . Thus, the determination of the optimum conditions for the production of elementary sulfur by the above reaction entail\ the determination of polythionic acids. Many methods have been proposed for analysis of the polythionates, but many of these are lengthy and time-consuming. Several indirect iodometric methods have been proposed (5,8,11). Other workers have used direct oxidation procedures using various oxidizing agents, including vanadate, iodate, and bromide-bro-
the mean. Analyses of pure polythionate samples indicate that the accuracy is of the same order as the precision. Typical analyses and comparisons with the method of Kurtenacker and Bittner are given. The proposed method is rapid, accurate, and readily applicable to routine testing, and is not affected by the presence of weak acids, as is the method of Kurtenaclier and Bittner. Possible interfering suhstances are discussed.
mate solutions ( 7 , 9, 12). Acidimetric methods involving a reaction with mercuric chloride have been proposed by Feld ( 4 ) and modified by Kurtenacker and Bittner (7’). For the present work, the acidimetric method seemed to offer the most promise, as it affords a quick, accurate procedure for total polythionates which may be easily applied to routine samples. The acidimetric method is more specific than the iodometric or direct oxidation procedures. THEORY AND DEVELOPMENT OF T H E METHOD
The reaction of the polythionates with mercuric chloride is well known :
+ 3HgCln + 4H20 = HgClz.2HgS + S H + + 4C1+ 4SU4-- + (272 -6)s where 7t = 3,4, and 5 for tri-> tetra-, and pentathionates. 2SnO6--
The increase in acidity in accordance with the above equation is thus a measure of the total polythionates present. Each mole of a polythionate radical thus produces 4 moles of hydrogen ion.
V O L U M E 25, NO. 2, F E B R U A R Y 1 9 5 3 The titration of the acid formed is complicated by the fact that the excess of mercuric chloride interferes as the p H is raised near the end point. T o avoid this interference Kurtenacker and Bittner ( 7 ) added a large excess of ammonium chloride and titrated to the methyl orange end point. This procedure is satisfactory for many samples but fails completely in the presence of weak acids or their salts because these cannot, be titrated to the methyl orange end point. For this reason it was necessary to develop a procedure which would be applicable to this type of sample as well as t o the usual i'un of samples. Hroniothymol blue was found to be fairly sat the titration of acetic acid. However, the ammonium chloride, atl(leti to keep the mercuric chloiitte in solution, interferes as the higher p€I of the bromothymol hlue end point is approached. If the :tmmonium chloride is omitted, mercuric oxide begin!: to precipitate and invalidates tht. titration before the end point can be r~ached. Hence it was necessary to find Pome other means of keeI)ing the mercuric chloride in solution and yet obtain a good elid point. \Tith this in mind it was found that a n excess of ~iot:issiumiodide added to thc. solution just before titration succesai'ully coniplexed the mercuric ion m t l still allowed a sharp end point, even in the presence of large quailtities of weak acids, when 1,2ic.nolphthalein was used a3 the indicator REAGEKTS
Sodium hydroxide, 0.1 .T, accurately standardized against potassium acid phthalate. C'arhnatc-fwe reagent is recomn w n d d for sharper end points. Saturated mercuric chloride solution. Potassium iodide, C.P. Phenolphthalein indicator, 5 grams dissolved in 500 ml. of 50% neutralized alcohol. PROCEDURE
\\ righ a sample containing 0 5 to 1.0 inillimole of polythionate (2.0 to 4.0 meq.) into a 250-nil. beaker or flask. Add Mater to make the volume approximately 30 ml. and neutralize to thr phenolphthalein end point. Add 20 ml of saturated mercuric chloride solution and mix well. Tart stand a t room temperature for 5 minutes, dilute to about 100 nil., and heat rapidly on the hot plat tetra-, and pentathionates. Thiosulfates if present are a direct interference, as they react with mercuric chloride in much the same manner as the polythionates, on the basis of the following equation ( 2 ) :
25203--
+ 3HgClz + 2H20 = 2SO4-- + 4 H + + 4C1+ HgC12.2HgS
Unless a correction is made on the basis of the above equation, the presence of thiosulfates will cause high results for polythionates. ~ h i ~ ~may ~ be l feasily ~ tdetermined ~ ~ by a n iodine titration, adding formaldehyde if necessary t o inactivate sulfites. Polythionates do not interfere in this titration, as they do not reduce iodine solution. smallamountsof sulfites do not interfere. L~~~~~amounts are not likely because the alkali sulfites react with tetrathionates and pentathionates to form thiosulfate and trithionate (IO). amounts Of sulfit'es broadens the The presence Of phenolphthalein end point, but this effect may be easily elimi-
ACKNOWLEDGMENT
The author wishes to express his appreciation to Sinclair Research Laboratories, Inc., for permission to publish this paper. REFERENCES
(1) Cacciavillani, B., Boll. soc. ital. biol. sper., 11, 754-6 (1936). (2) Ephraim, Fritz, "Inorganic Chemistry," 4th ed., revised p. 556, New York, Nordemann Publishing Co., 1943. (3) I b i d . , P. 562. (4) Feld, W., 2. angew. Chem., 24,290 (1911). (5) Goehring, Margot, Z . anal. Chem., 128,6-9 (1947). (6) Goehring, M ~ and ~Feldmann, ~ Ursula, ~ ~z, anor*, , allgem. Chem., 227, 223-6 (1948) ( 7 ) Kurtenacker, A. ,and Bittner, K.. Ibid., 142, 119-29 (1925). (8) Kurtenacker, A, and Goldbach, E., Ibid., 166, 177-89 (1927). (9) Lang, R., and Kurtenacker, H., 2. anal. Chem., 123, 169-87 (1942). (10) Raschig, F., 2. angezu. Chem., 33,260 (1920). (11) Samuelson, O., and IVestlin, A., Saensk Papperstidn., 50, K lI-B, 149-54 (1947). (12) Sin&, B.9 and Ilahi, I., J . I n d i a n Chem. SOC., 14,376-80 (193ii. (13) Stamm, H., Goehring, M., and Feldmann, U., 2. anorg. allgem. Chem., 250, 226-8 (1942). (14) Stamm, H., Magers, ITT. IT,,and Goehring, M.,Ibid., 244, 184-90 (1940). (15) Stamm, H., Seipold, O., and Goehring, R.I., Ibid., 247, 277-306 (1941). (16) villiers,A., c o m p t . rend., 106,851, 1354 (1888); 108,42 (1889).
.
RECEIVED for review June 17, 1962. Accepted October 20, 1952. Presented before the Division of Refining, American Petroleum Institute, $an Francisco, Calif., 1952.
Industrial Chrome Ore Analysis An Industry Standard Sample of Metallurgical Chrome Ore WINSLOW H. HARTFORD Research Laboratories, Mutual Chemical Co. of America, Baltimore, M d .
S
EVERAL years ago Lundell (20) pointed out some of the variables influencing the analysis of industrial materials, and stated "the ordinary analyst of things as they are is not so much concerned with keeping his errors below one part in one thousand as he is in keeping them below one part in one hundred." That the problem is still very much present has been shown by Schlecht ( 2 2 )in the difficult field of silicate rock analysis. I n the analysis of industrial raw materials, such as chrome ore, the matter of accurate analytical methods is important, because errors of the order of 1% in the analysis of a single cargo may represent a discrepancy of several thousand dollars. This paper presents some of the information which has been obtained over the past several years with the purpose of reducing the
discrepancies between laboratories. It is in three sections: a study of the experience of representative laboratories in the analysis of ore cargoes over several years, a discussion of several analytical procedures now being used for the analysis, and information on cooperative analysis leading to the establishment of an industry standard for metallurgical chrome ore. RECENT EXPERIENCE IN CHROME ORE ANALYSIS
During the period from 1945 t.o the present, chromic oxide has been determined in 304 samples of chrome ore by this laboratory and a t least one other. The following table summarizes the results:
