ANALYTICAL EDITION
March 15, 1942
TABLE111. LAKES" AiYD COLORS O F 3,'kDIHYDROXYBENZALRHODAKINE IN ALKALINE SOLUTIONS OF CATIOKS 9
Cation Al+++ Co++ Mg + +
hln++ Ni++
Excess N a O H Purpie-ikd lake Purple-red lake Purple-red lake Lavender lake
Excess NH4OH Red-brown lake
Excess Pyridine Brown lake
Red lake Pink ppt. Lavender lake Violet p p t . Purple soln.
Deee'biie' s o h . Violkt ppt. Blue soln.
.....
More metals were precipitated b y the hydroxybenzalrhodanines than b y rhodanine itself. The very slight water-solubility of the compounds materially restricts their use as analytical reagents.
..... .....
5 Lake formation was taken t o be affixing of characteristic color t o pre cipitate, so t h a t a clear solution resulted upon filtering.
Summary The analytical possibilities of 0-, m-, and p-hydroxybenzalrhodanines and 3,4-dihydroxybenzalrhodanine were studied.
207
Literature Cited (1) Borgellini, G., Chem. Zentr., 77,Part 1, 1436 (1906). (2) Feigl, F., "Qudit,ative Andyse mit Hilfe von Tupfelreaktionen", 2nd ed., p. 91,Berlin, Julius Springer, 1935. (3) Feigl, F., 2. anal. Chem., 74,380 (1928). (4) Fettig, R.,and Remsen, I., Ann., 168,97 (1873). (5) Griess, P.,Bm., 12,427 (1879). (6) Hann, R.M., J . Am. Chem. Soc., 47,1998-2002 (1925). (7) Nencki, M., J.prakt. Chem., (2)16,4(1877). (8) Rosemand, K.TV., and Boehm, T., Ann., 437,142 (1924). (9) Tschuzaeff. L.. Ber.. 38. 2520 (1905). (10j Fgscrheider, R., Monatsh., 14,382(1893). (11) Zipser, A , , Ibid., 23,960 (1902).
Electrolytic Determination of Iron A Modified Moore Method WILLIAM H. ARMISTEAD, JR.', Vanderbilt University, Nashville, Tenn.
M
iiNY of the volumetric methods for iron are highly satis-
factory for routine determinations. However, they all require standard solutions, and, when iron is determined only occasionally, considerable time is often spent in standardizing the required solution. The electrolytic method presented here requires stock solutions which can be stored indefinitely, and should be particularly convenient in laboratories where electroanalysis of other metals is routine. Both accuracy and precision of 1 to 2 parts per lhousand are readily attained in the presence of the usual substances in iron ores. Only the customary silica separation, followed b y decomposition with hydrofluoric and sulfuric acids to recover the iron combined as silicate, is necessary; chloride does not interfere. The method is based on the deposition of metallic iron from the complex formed b y the addition of excess ammonium carbonate solution to an acid solution containing ferric iron and orthophosphate ions. The hot solution is electrolyzed a t a high current density without stirring. Moore ( 3 ) suggested the use of a ferric phosphate-ammonium carbonate solution for the electroanalysis of iron. Brand (2) used pyrophosphate instead of phosphate. He stated that the last traces of iron were difficult to deposit and that the solution dissolved the metal when current was not flowing. Avery and Dales (1) criticized Moore's method. They found that 5 hours were required to deposit 200 mg. of iron. Their deposits were high in weight, althou h deposition was incomplete. They found a slight amount of ca%onaceous material and some phosphorus in their deposits.
Experimental SELECTION O F h l M O N I U M CARBONATE STOCK SOLUTION. T h e addition of excess ammonium carbonate solution t o a n acidic ferric phosphate solution forms a soluble complex, which is much more soluble in cold than in hot, and in concentrated than in dilute ammonium carbonate. Since electrolysis of the cold solution is unsatisfactory, i t is necessary to prepare a solution sufficiently concentrated to hold moderate amounts of the ferric complex in solution at 70" C. (just below t h e ebullition temperature). V7hen i t precipitates before or during electrolysis, many hours are usually required for resoPresent address, Corning Glass W70rks, Corning, N. Y.
lution and complete deposition of the iron. This precipitation is possibly the cause of the criticism of Moore's method (1).
When the concentration of ammonium carbonate in the electrolyte is at least 3.5 M , the solubility of the complex is such that no precipitation of iron occurs at 70" C. from a solution containing as much as 200 mg. of iron in a volume of 200 ml. I n order to prepare conveniently an electrolyte of such concentration, a 5.0 M stock solution is necessary. PREPARATION OF STOCKSOLUTIONS.The 5.0 M ammonium carbonate stock solution, XH3/COz = 2.05-2.1, was prepared by dissolving 1570 grams of Eimer & Amend reagent quahty lump ammonium carbonate, assay 31.8 to 32.5 per cent ammonia, in 700 ml. of clear reagent quality concentrated ammonium hydroxide, specific gravity 0.90, and sufficient water to make 4 liters. A higher concentration of free ammonium hydroxide is undesirable. With only occasional. shaking, several days. were required for complete solution, Heatin to 65' C. and/or stirring facilitate solution but must be employe$ with suitable precautions because of the volatile nature of ammonium carbonate. The 2.0 -11 ammonium dihydrogen phosphate stock solution nas prepared by dissolving 230 grams of the low-arsenic salt in water and diluting to 1 liter. Other sufficiently pure alkali phosphate salts or phosphoric acid also were found to be satisfactory. PREPAR.4TION AND STANDARDIZATION FERRICAMMONIUM TESTSOLUTION.In 2 liters of mater containing 278 ml. SULFATE of concentrated sulfuric acid 890 grams of ferric alum were dissolved. After filtering, the solution was diluted to 10 liters and used in all the analyses reported; it was 1.0 N with sulfuric acid. It was standardized by the stannous chloride-potassium dichromate procedure of.Willard and Furman (4). The reduction and titration were carried out at 25" C. The averaged result of four determinations was 0.1033 gram of iron in 10 ml. APPARATTJS. The cathode was a 10- ram cylindrical platinum wire gauze, surface area 80 sq. cm. T%e anode was a 1.25-mm. diameter platinum wire loop, surface area 4 sq. cm. The electrolytic stand was arranged so that the electrodes could be r e moved without interruption of the current. Current was taken from a lead storage bank capable of supplying 6 amperes a t 10 volts. Larger electrodes and a higher current are desirable. A 400-ml. Pyrex brand tall-form beaker was used as electrolyte container. A 1.5 x 15 cm. indented upright glass column (similar to that of the familiar Claisen distillation flask) sealed just below the rim served as a spray trap, while evolved ammonia wm drawn off by gentle suction through a side tube near the top. This device was not necessary, but prevented escape of ammonia into the laboratory during electrolysis, since it was not convenient to use a hood. The beaker was covered with a suitably notched split n atch glass.
INDUSTRIAL AND ENGINEERING CHEMISTRY
208
TABLEI. EXAMINATION OF ANODICDEPOLARIZERS Time of ElectrolyDepolarizer Addpd
81.9
(NH4)zS Test
Man. Negative Welch's NazSOa 35 Green 30 E. & A . c P. Na2SO3 Negative 35 30% SO2 NHrHSO3 Green 35 Merck's NazS0s 7Hz0 Negative E. & A. reagent NaHSOs 35 45 Baker's K2SOa.2HzO Pale green 80 Hydrazine sulfate Negative 75 Ammonium oxalate5 Pale green Urea Negative 1 gram K I 105 Pale green Sodium formate 60 Negative Sodium hypophosphite 40 Pale green Ammonium phosphite 75 Did not completely dissolve during electrolysis
Grams
+
a
Weight of Error in Fe Deposit Fe Gram Mp. 0.2104 +3.8 +2.s 0.2094 +3.2 0.2098 +0.7 0.2073 0.2115 +4.9 0.2078 $1.2 0.2074 +0.8 0.2063 -0.3 0.2069 +0.3 0.2066 0.0 0.2123 +5.7 0.2071 +0.5
General Procedure A sample containing 100 to 200 mg. of iron was weighed and dissolved in the clean electrolytic beaker. All iron was oxidized to the ferric condition with persulfate or hydrogen peroxide, the excess being destroyed by boiling. Nitrate must be absent. The solution was cooled, and 15 ml. of stock phosphate solution were added to the cold weakly acidic solution and mixed thoroughly; the volume should now be 50 ml. or less. There must be 3 to 5 moles of phosphate for every gram-atom of metal other than the alkalies. Then 150 ml. of stock ammonium carbonate solution were added, the first part cautiously from a buret to avoid spattering. Not more than 10 ml. should be required for neutralization. The clear tan solution was covered with the split watch glass and heated to 67-70" C. (not higher). Both electrodes were placed a ainst the bottom of the beaker. If this is not done, the slowness o f upward diffusion of metal ions into the effective electric field will greatly prolong the time required for complete deposition. The solution was electrolyzed for 90 minutes with a current of 6 or more amperes ( N . D.100 = 5 to 10) or until deposition was complete. Incomplete deposition is indicated by a green or black color formed upon addition of clear ammonium sulfide to a small portion of the electrolyte. Electrolysis was continued 15 minutes after the first negative test, the deposit being kept covered during electrolysis by use of wash water on the cover glass and sides of the beaker. The current was reduced to 1 ampere and the electrodes were removed without interruption of the current while being continuously washed with a heavy stream of water. The cathode was washed thoroughly with water, then with 95 per cent ethyl alcohol, dried 30 to 35 em. above a spread burner flame, and u eighed.
the sulfite and arsenic in the hypophosphite. The deposits from the sulfite solutions were dark, contained sulfur, and were slightly rusty. Obviously, the depolarizers were added after the ammonium carbonate, since many of them would reduce ferric ion in acidic solution.
SEPARATION OF IROSFROM OTHERMATERIALS BY ELECTable I1 shows that the method is satisfactory in the presence of large amounts of ammonium chloride and
TROLYSIS.
ammonium sulfate. The upper limits for noninterference of aluminum, chromium, and titanium are 50 mg. of aluminum trioxide, 40 mg. of chromium, and 20 mg. of titanium dioxide. I n Table I11 it is shown that moderate amounts of manganese interfere. Crystals of manganese ammonium phosphate, formed during electrolysis, in part adhere to the cathode, causing high results. The time when these crystals were first detected is shown. Ten minutes elapsed between the addition of carbonate and start of electrolysis. It is obvious that it is necessary to deposit the iron completely and stop electrolysis before this crystallization starts in order to obtain accurate results for iron. The presence of other metals, such as aluminum, chromium, and titanium, apparently helps in holding manganese in solution. This effect was not studied quantitatively. An iron ore containing up to about 1 per cent of manganese may be analyzed without interference.
TABLE 11. SEPARATIOX OF IRON FROM OTHERMATERIALS BY ELECTROLYSIS Material Added
(SHdzS Teat
AVQ '.
Green Negative Kegative Negative Green Negative Negative Negative Negative
10,000 'NHrC1 10,000 NHiCl 10,000 (NHa)tSO4 10,000 (NHr)zSOa 70 A 1 2 0 3 50 AltOa 50 .4b03 50 Cr .... 40 Cr .... 40 Cr 20 Ti02 Negative 10 TiOt Negative 10 Ti02 Negative a 10 ml. of stock ohosohate used b Electrolyzed 60'min;tes C Electrolyzed 75 minutes. d Added as potassium alum solution 8 Added a s 5% sulfuric acid solution
Results of Analyses I n all the analyses described below, unless otherwise noted, the same conditions were employed-namely, 20 ml. of standard ferric alum solution (0.2066 gram of iron), 15 ml. of stock phosphate solution, 150 ml. of stock carbonate solution, a 200-ml. volume of electrolyte, and 90 minutes of electrolysis a t 67-70' C. with a current of 6.0 amperes at 5.2 volts. The temperature, current, and voltage remained nearly constant during electrolysis. The ammonium sulfide test was made on the entire electrolyte after removal of the electrodes. Under these conditions, it is sensitive to 0.1 mg. of iron. The iron deposits obtained, unless otherwise stated, were always bright, dense, adherent, highly pure, and readily washed and dried without rusting. Hydrogen sulfide must be absent from the laboratory atmosphere to avoid contamination of the deposit with sulfur. K h e n present, arsenic partly codeposits with iron. EXAMIXATIOK OF AKODIC DEPOLARIZERS. Since nitrate formed by anodic oxidation of ammonia depolarizes the cathode and retards iron deposition, various reducing agents were examined in an attempt to eliminate this difficulty. The results are shown in Table I. Of all the depolarizers examined, only sulfite and hypophosphite were effective in reducing the time required for complete deposition, but neither was satisfactory because impure iron deposits were obtained, sulfide being present in
Vol. 14, No. 3
Weight of Fe Deposit Gram 0.20626 0.2066C
0.2066C
0.2065 0.2060C
0.2065 0.2059 0,2066 0.2065
0.2058 0,2066 0.2067 0.2069 0.2066 0.2068
Error in Fe
MQ. -0 4 0.0 0.0
-0.1 -0.6 -0.1 -0.7 0.0 -0.1 -0.8 0.0
+o.
1
+0.3 0.0 f0.2
TABLE 111. SEPARATION OF IRON FROM MANGANESE BY ELECX n Added (as MnSOd) Fe Added Mu. Gram 10 0.2066 5 5 J
4
4
0.2066
0.1033 0.1038 0.2066 0 2066
TROLYSIS MnNHIPO1, Ap- Time of peared Elec(XH4)PS after: trolysis Test Min. Min. 50 90 Neg. 75 90 Neg. Seg. 60 60 60 60 NW. Feg. 75 90 75 75 Neg
Weight of Fe Deposit Gram 0.2104 0,2078 0.1034 0.1033 0.2069 0.2065
Error in Fe
Ma. +3.8 +1.2
+O.l
0.0 +0.3 -0.1
It is probable that magnesium would not interfere to the same extent as manganese, since magnesium ammonium phosphate is appreciably soluble in hot ammoniacal solution. If it is desired to determine other metals remaining in the electrolyte after separation of the iron, the ammonium carbonate may be boiled off and the precipitated metallic phosphates dissolved by cautious addition of mineral acid. Any silica is removed by filtration before proceeding.
Codeposition of Iron and Other Metals I n Table IV data are given for the codeposition of iron with nickel, cobalt, molybdenum, and tungsten. With nickel or cobalt, the iron alloy deposited more rapidly than nickel or
209
ANALYTICAL EDITION
March 15, 1942
Summary TABLE IV.
CODEPOSITION OF IRON AND OTHERMETALS
Weight of Total Deposit Error Gram Mg. Positive Segative 0.1163 - 0.6 0.1116 0.1 Negative Negative 0.1114 0.3 Segative Negative 0.1077 f 0.2 Segative xegative Segative 0.1037 - 6.4 Negative 0.2114 1.0 Negative 0.3154 0.3 Negative 0.3159 f 0.2 b,c Black 0.0950 -30.1 c Kegatire 0.2181 4- 0 . 6 c,d Negative 0.1144 f 0.2 C,O h-egative 0.1072 - 3.6 C,O Negative 0.1068 4.0 4 Second metals added as Ni804, COSOI. Na2JloO4, and NazN-04 standard solutions to ferric alum before addition of phosphate. Electrolyzed: b 140 d 75, and e 60 min., respectively. e Used 10 mi. of stock phosphate. Weight of Second Weight of Metal Added" Fe Added Gram Gram 0.0126 S i 0 . 1033 0.0084 K i 0.1033 0.0084 pu'i 0.1033 0.0042N i 0,1033 0.1091 c o 0.1091 C O o.io33 0.1091 Co 0.2066 0.1091 Co 0.2066 0.0218 hlo 0.1033 0,0109 110 0.2066 0.0109 410 0.1033 0,0075 W 0.1033 0.1033 0,0075 W
Dimethylglyoxime Test
(SHa)2S Test
-
-
..
-
cobalt alone. Ammonium sulfide is still only a test for iron;
c p to 10 mg. of molybdenum are quantitatively codeposited with 100 mg. or more of iron. Amounts of molybdenum above about 20 mg. depolarize the cathode and prevent complete deposition of iron. The range between 10 and 20 mg. of molybdenum in 200 ml. of electrolyte \vas not examined. In this range, the transition from the platable to the depolarizing concentration occurs' It might be to examine the from a possibility Of plating trolyte containing a very low concentration of molybdate.
Iron can be quantitatively determined as metal by electrodeposition from a hot complex ferric ohosohate-ammonium carbonate solution at a h g h - current density without stirring. The method is accurate and reasonably fast. The highly sensitive ammonium sulfide test is available to prove completeness of deposition. The method may be applied to low manganese iron ores without removal of hydrochloric acid. Small amounts of nickel or molybdenum are quantitatively codeposited with large amounts of iron, and cobalt with a t least twice as much iron. Tungsten must be absent. Large amounts of chloride] sulfate, and phosphate do not interfere. S i t r a t e and all strong oxidizing agents must be absent.
Acknowledtzment
Literature Cited
s., and Dales, B,, Ber., 32, 64 (1899).
(2) Brand, A,, z. anaz. Chem., 28, 581 (1889). (3) Moore, T., Chem. News, 53, 209 (1886). (4) Willard, H. H., and Furman, N. H., "Elementary Quantitative Analysis", 2nd ed., pp. 194-5, New York, D. Van Nostrand Co., 1935. FROM a thesis presented b y William H. drmistead, Jr., to t h e Graduate School of Vanderhilt University in partial ful6llmeut of t h e requirements for t h e degree of doctor of philosophy.
Determination of Ash in Coals Unusually High in Calcite and Pyrite 0. W. REES, Illinois State Geological Survey, Urbana, Ill., AND W. A. SELVIG, U. S. Bureau of Mines, Pittsburgh, Penna.
I
S D E T E R M I N I N G ash in coals containing unusually large amounts of calcite and pyrite, difficulty in obtaining satisfactory results b y the standard A. S. T. RI. procedure (3) may be experienced] because of the varying amounts of sulfur that are retained as calcium sulfate in the ash. Variations in the heating procedure used in the ash determination influence t h e amount of sulfur retained. Lower ash and lower sulfur in the ash are obtained b y slow rates of heating. This paper is a report of cooperative work done b y the Analytical Laboratory of the Illinois State Geological Survey and the Pittsburgh Laboratory of the United States Bureau of Mines for the purpose of studying modified procedures for the determination of ash in such troublesome coals.
Bureau of Mines Determinations
Experimental Tests For this work five sizes of coal prepared by screening from it 1 1 / 4 inch X 0 screenings from the KO. 2 bed, Woodford County, Ill., were used. The larger sizes were crushed t o pass a No. 4 sieve and after mixing and riffling all sizes, two 1-quart samples of each were cut out. One set of samples was sent to the U. S. Bureau of Mines Laboratory and one set was retained in the Illinois State Geological Survey Laboratory. large sample of
The samples are designated as follows: Sample 1 2 3
Sine
Sample
X
t
incli x inch a/'n inch X 10-mesli ll/r 314
314 3/n
Each laboratory prepared its own samples for analysis b y the usual A. S.T. M. procedure ( I ) . Analyses in the two laboratories indicated that the two samples of each size were satisfactory duplicates, with the exception of sample 3. Because the two 1-quart portions differed in ash content by too large a n amount, the ash values reported by the Geological Survey laboratory were obtained on the 60-mesh coal prepared in t h e Pittsburgh laboratory. The coals were analyzed for total sulfur (Eschka method), and for forms of sulfur and carbon dioxide by methods of the U. S. Bureau of Mines ( 7 ) . Moisture at 105' C. mas determined b y each laboratory on the samples according t o the A. S. T. 11.standard method ( 2 ) .
Size 10 X 48-mesh - 48-nicsh
METHOD A. The dried samples were heated on the hearth of a hot muffle furnace for 8 minutes t o drive off volatile matter, then heated at 725' C. t o constant weight (within 0.001 gram). METHODB. The dried samples were placed in a cold furnace and heated t o 725" C. in 1.5 hours. The temperature was kept at 725" C. t o constant weight. METHODC (Parr's sulfated ash method, 5 , 6). The dried samples were burned by Method A and after cooling \yere moistened with a few drops of 1 to 1 sulfuric acid and dried on an air bath until the fumes were largely driven off. The samples were then heated at 725" C. t o constant \wight. This treatment produces a sulfated ash in 1% hich it is assumed that all calcium is present as the sulfate. To correct to a calcium oxide basis the percentage of sulfur trioxide, coal basis, determined in the sul-
,
