1972
ANALYTICAL CHEMISTRY
sented lubricating oils containing a barium sulfonate additive in moderately high concentrations. The third sample contained a suspension of barium sulfate in mineral oil. Other tests were run on blends consisting of barium sulfonate mixed with an oil of high disulfide content. These blends ranged in concentration from approximately 4 t o 20% sulfur. Analytical data on these materials are given in Table 111. On the basis of the above data, the standard deviation for per cent of sulfur is as follows: 70s 0 to 1 1to 5 Over 5
Table 111. Application to Organic Systems Containing Barium Sulfur Wt. % of Sample Added Found Barium sulfonate in lubricating oil 1
2 Barium sulfate suspended in mineral oil Barium sulfonate and disulfide oil
0.006 0.06 0.10
INTERFERENCES
ACKNOWLEDGMENT
The authors wish t o express their appreciation t o E. T. Scafe and Perry Swanson for their cooperation and assistance in the
1 4 4 . 1 51 1 8 0 , l 85
4 84
0.14
0 13,0.14
0 59
7 48
3 4
preparation of this paper, and t o A . G. Herzog for obtaining part of the analytical data. LITERATURE CITED (1) Am. Sac. Testing Materials, Philadelphia, Pa., “Standards on Petroleum Products and Lubricants,” Method 129-52, 1954. (2) Chalmers, A,, and Rigby, G. W., IXD.ENG.CHEM., ASAL.ED , 4, 162 (1932).
CONCLUSION
Total d f u r may be readily determined in materials of high thermal stability by combustion with vanadium pentoxide at 900” t o 950’ C. Elements such as calcium, barium, sodium, and aluminum do not interfere, although acid-forming elements do cause interference. The method is applicable t o organic as well as inorganic substances. I n materials containing molybdenum sulfide, the presence of chromium in the combustion mixture is necessary. Application of the method to the sulfur assay of paints, ceramics, shale, and minerals is suggested.
1.51 1.82
1 2
Std. Dev.
Other acid-forming constituents interfere, in which case a gravimetric determination of the evolved sulfur is required.
Rt. % of Barium Present
(2) Gatterman, L., “Laboratory Methods of Organic Chemistry,” pp. 65-8, blacmillan, Xew York, 1932. (4) Grate, W., and Krekler, H., Angew. Chem., 46, 106 (1938). (5) Hagerman, D. B., ANAL.CHEX.,19, 381 (1947). (6) Kirsten, W., Ibid., 2 5 , 7 4 (1953). (7) Kirsten, W., Mikrochim. Acta, 35, 175 (1950). unpublished paper, Institute of lledical Chemis(8) Kirsten, W., try, University of Uppsala, Uppsala, Sweden. (9) Luke, C . L., IND. ENG.CHEM.,A N ~ LED., . 5 , 298 (1945). (10) Peters, E. D., Rounds, G. C., and .Igasai, E. J., A s ~ L .CHEM., 4, 710 (1952). (11) Rice-Jones, TV. G., Ibid., 25, 1383 (1953). (12) Zinneke, F., Z.anal. Chem., 132, lis (1951).
RECEIVED for
review M a y 12, 1955.
Accepted September 1 1955
Determination of lead in lead Sulfide Ores and Concentrates CHARLES A. G O E T Z and FREDERICK 1. DEBBRECHT lowa State Co//ege, Ames, b w a
The present work was begun to develop a more accurate and rapid method for the determination of lead in lead sulfide ores and concentrates. .-i method employing the perchloric acid dissolution of the sample, electrodeposition of lead as lead dioxide, and complexometric titration of the lead with HexaVer is proposed. The entire procedure for the determination of lead can be completed in less than one hour with a precision of about one part in a thousand. A longer procedure is given for the elimination of arsenic, antimony, and tin if these elements are present in sufficient amounts to interfere in the deposition of lead. The method avoids the time-consuming and inaccurate acetate extraction from separation of lead from barium. Not only is the complexometric titration faster than drying and weighing the lead dioxide deposit, but it also avoids the use of an empirical factor for the deposit.
T
H E soparation of lead from barium in the presence of sulfate ions based upon the acetate extraction of the lead has been shown to be incomplete (f, 5 ) . The Separation of lead as lead dioxide by electrodeposition with subsequent weighing is objectionable, because of the empirical conversion factor that varies with the conditions. This factor varies from 0.845 ( 3 )up to the theoretical factor of 0.8662 ( 7 ) . Loomis ( 4 ) shoJTed that lead and copper couldbesimultaneously
deposited on the anode and cathode, and that the lead could be determined volumetrically using HexaVer (disodium dihydrogen 1,2-diaminocyclohexane iV,,V,‘,S’,S’-tetraacetate), by adding an excess of the HexaVer and back-titrating tT-ith standard magnesium chloride solution. Flaschka ( 2 ) titrated lead directly using Versenate [disodium dihydrogen (ethylenedinitrilo) tetraacetate] in the presence of tartrate to keep the lend in solution at a p H of 10. The authors found that the lead ore samples used for student analysis (prepared and sold by Hach Chemical Co., .hies, Iowa) could be dissolved rapidly and completely in about 5 minutes using boiling 72% perchloric acid, and that the lead could be quantitatively separated from the barium, iron, arsenic, bismuth, and silica present in the ores even when appreciable amounts of sulfate ion were present. The lead dioxide was viashed and dissolved using nitric acid and hydroxylanimoniuni chloride, and the lead determined by direct titration using Hexaver. MATERIALS AYD APPARATUS
Solutions. STANDARD HEXAVER. rlnalytical reagent grade HexaVer (obtained from Hach Chemical Co., h i e s , Iowa) was used in preparing the standard solution, by dissolvihg about 7.8 grams per liter of distilled water and then standardizing against the primary standard lead nitrate, standard calcium chloride solution, and the gravimetriaally standardized lead perchlorate solution. LEADPERCHLORATE. Twenty-one grams of test lead riere dissolved by boiling in 72% perchloric acid for a few minutes. The
1973
V O L U M E 27, NO. 12, D E C E M B E R 1 9 5 5 solution n a s cooled and diluted with about 30 ml. of water, boiled to remove chlorine, and diluted to about 5 liters. This solution n as standardized by precipitating the lead as the sulfate and n-eigliing as such The solution was found to be 0.01581M. SODIL-\ITARTRATE. In 1 liter of water 46 grams of sodium tartrate monohydrate were dissolved to give approximately a 0.2M solution. SoDIr\r HYDROXIDE.To give a 531 solution 200 grams of sodium hydroside were dissolved in water and diluted to about 1 liter. S T A S D ~CRADL C I UCHLORIDE. ~I An accurately weighed amount (0.4 to 0.5 gram) of primary standard calcium carbonate (Mallinckrodt low alkali grade, dried a t 110' C. for 2 hours) mas dissolved in 50 nil. of water containing 5 ml. of 5111 hydrochloric acid. The solut,ion was boiled to expel carbon dioxide, cooled, and diluted t o exactly 250 ml. .In Eriochrome Black T indicator preparation, ISDIC.~TOR. AlanYer, commercially available from the Hach Chemical Co., Amee, I n w a >\vas used. BUFFER( p H 10). The pH 10 buffer solution was prepared by adding 67.5 grams of ammonium chloride to 5 i 0 ml. of concentrated ammonium hydroxide and diluting to 1 liter. Primary Standard Lead Nitrate. Test lead was dissolved by
Standardization of HexaVer Solution. The Hexaver solution was standardized against the standard calcium chloride solution by pipetting exactly 25 ml. of the calcium chloride solution into a clean flask and adding 1 ml. of the buffer solution and about 0.26 gram of sodium cyanide to eliminate interference from traces of copper present in the distilled water. To this were added about 25 mg. of the magnesium salt of HexaVer and about 5 drops of the indicator. The solution was then titrated with HexaL7er until the pink color turned to a pure blue. The results of eight consecutive titrations are given in summary form in Table 11.
I I 10.5 11.0 pn
metal.. Electrodes. The anodes used m r e platinum gauze (45-mesh wire, diameter 0 . O O i i inch) formed into cj-linders l j / 8 inches in diameter rrnd 2 inches long. The cathodes were similar, but were only 0.5 i,nch in diameter and mounted to provide stirring during all depositions. The anodes were roughened by sandblasting. EXPERIlIEh-TA L
Dissolution of Ore. Concentrated, as well as dilute (1 to l), nitric and hydrochloric acids were tried as solvents for the o-e samples, b u t concentrated ( 7 2 % ) perchloric acid was found to be far superior to the nitric and hydrochloric acids as the solvent. The results of t,he dissolution studies are given in Table I. I n each c:iae about 0.2 gram of the ore was placed in a 300-ml. tallform henfirr, 20 ml. of the solvent viere added, and the beaker was placed oil an electric hot plate adjusted to give a surface t,eniperat,ure of about 260' C. The silica residue formed in the perchloric acid solution method was filtered off, treated lq-ith hydrofluoric and sulfuric acids, and tested for lend using chromate. No lead was found. T o di.solre the ore samples promptly and completely 10 ml. of the i 2 ' 3 perchloric acid can be used. When large amounts of silica are present, bumping can be decreased by using 20 ml. of the acid, or 1 ~yadding glass beads. Currenr use of organic flotation reagents may leave a residue of these reagents on the lead sulfide. The question of the action of, T2Y0 perchloric acid on these organic residues immediately arises; t h w , 10 different lead sulfide "flotation concentrates" were t.ested n.ith hot 727& perchloric acid. One-gram samples (considerahly in excess of the recommended sample size) went into solution easily and snioot,hly with no sign of any difficulty.
Table I. Solrent 72% HC'l@r Coned. H S O i
Dissolution Studies of Lead Sulfide Ores Dissolution Time. Minuter fi
15
1 to 1 HSO;
45
Coned. H C I 1 t o 1 HC 1
S o t soluble X o t soluble
Table 11.
Remarks C'ompletely dissolved except for silica residue 130 minutes addibional required t o dissolve sulfur bead formed 120 minutes additional heating failed t o dissolre sulfur bead formed After 120 minutes ore was not in solution After 120 minutes ore was not in solution
Comparison of Standardization Methods for HexaVer
.\Iethod Primary e t d . , CaCO3 Primary std. P h ( S O a ) ? 0.01981.1f Ph.ClOp)t.3H?O
s o . of
Dptn. 6
' 5
Av. lfolarity 0.01987 0.01988 0.01989
A\-. Del-. 0.00001
0,000014 0.000004
Std. Dev. 0.000013 0.000016 0,000007
Figure 1. Effect of variation of pH on titration of lead with HexaVer and Versenate
Direct Titration of Lead with HexaVer. About 0.2 gram of the primary standard lead nitrate was accurately weighed and dissolved in about 50 ml. of water. To this were added 10 ml. of the 0.2M tartrate solution, and 5 M sodium hydroxide was added dropwise until the precipitate of lead tartrate first formed just redissolved. About 1 ml. of the buffer was added, followed by about 0.25 gram of sodium cyanide, and 5 drops of the indicator. This lead solution was then titrated with the Hexaver solution until the violet color changed to a clear blue-green. The results of nine consecutive titrations are given in summary form in Table 11. Also given in Table I1 are the results of five titrations which were similarly titrated using 50-ml. aliquots of the lead perchlorate solution. Comparison of HexaVer and Versenate at Various pH Values. Aliquots of 25 ml. of the lead perchlorate solution were titrated with the standard Hexaver solution and with a standard Versenate solution a t various pH values. The difference in the amounts of solution required to obtain the end point at various pH values (using p H 10 as the reference) is sham-n in Figure 1. A sharp end point was obtained only in the pH region from 5.0 to 10.7. From this study it is apparent that p H control is less critical using HeuaVer. I t also was observed that sharper end points are obtained with HexaVer in the direct titration of lead. Electrodeposition Studies. EFFECT OF ACIDSON DEPOSITIOXS. It was established that perchloric acid was the ideal solvent for the ore samples; hence, in the lead deposition studies 25-m1. aliquots of the lead perchlorate solution were used in each of the studies. Varying amounts of concentrated nitric and 72% perchloric acids were added, and the solution was diluted to about 125 ml. in order to nearly cover the anode in the 300-ml. tallform beakers. It was anticipated that appreciable amounts of sulfate would be present in the solutions resulting from the dis-
1974
Eolution of ore samples; thus 0.25 ml. of concentrated sulfuric acid was added to each run. In each of the studies (Table 111) a current of 2.5 amperes n-as used for 1 hour. I n each case the deposited lead dioxide was dissolved and titrated with HexaVer using the procedure for ore analysis. I t is apparent from the data presented in Table I11 that complete deposition does not result under the test conditions unless the solution is contained in excess of 25 ml. of concentrated nitric acid. The presence of varying amounts of perchloric acid appears to have little effect on the deposition. CURRENT VERSCS TIME. The deposition of the lead was studied using 3, 4, 5, 7.5, and 10 amperes of current to determine the corresponding required deposition time. In each case 35 ml. of nitric acid and 20 ml. of 72% perchloric acid were added to the 25-ml. aliquot of the lead before dilution to about 125 ml. The lead dioxide was dissolved and titrated by the procedure for ore analysis. The data (Table IV) show that about 0.1 gram of lead can be quantitatively deposited very rapidly a t current rates up t o 10 amperes. I n other studies as much as 0.5 gram of lead was deposited on the anode.
INTERFERIKG ELEMENT STUDIES. A qualitative analysis of the ore samples showed that considerable amounts of iron and barium were present, but only traces of arsenic and bismuth were found. To determine whether these ions would interfere in the lead deposition and its subsequent titration, a series of studies was made using the primary standard lead nitrate as the lead source. T o accurately weighed samples of the lead nitrate varying amounts of the foreign ions and 0.25 ml. of concentrated sulfuric acid were added. The mixture was dissolved by boiling with 20 ml. of 72% perchloric acid. The results are given in Table V. The barium ion interference resulted only when a barium sulfate precipitate was formed. The 0.25 ml. of concentrated sulfuric acid added in these studies far exceeds the amount of sulfate likely to be present or formed when ores are dissolved. Further interference studies were made using a lead ore sample as the source of lead. T o the accurately weighed sample, varying amounts of arsenic, antimony, bismuth, silver, manganese, tin, and barium were added and the mixture was analyzed, using the procedure for determination of lead in lead sulfide ore. The results are given in Table VI. The error introduced by interferences is significant if it is more than 0.2 mg. Greater amounts of interfering ions than listed in the table cause a proportionately larger amount of error in the lead deposited. Silica interference is discussed in the section, Dissolution of
Ore.
ANALYTICAL CHEMISTRY Table 111. Variation of Acid Concentrations for Deposition of Lead "Os, HC104, Lead, Gram Error, NO.
.MI.
111.
7 8 9 10 11 12 13 14 15 16 17 18
20 25 30 20 25 30 20 25 30 20 25 30
5 5 5 10 10 10 15 15 15 20 20 20
Table IV.
1 2 3 4 5 6 7 8 9 10 11 12 13 14
?io.
1
2 3 4 5
6 7 8
Found 0.1001 0.1008 0.1011 0.1020 0.1026 0.1026 0.1022 0.1024 0.1026 0.1023 0.1024 0.1026 0.1023 0.1024 0.1026 0.1024 0.1026 0.1026
Jlg. 2.5 1.8 1.5 0.6 0.0 0.0 0.4 0.2 0.0 0.3 0.2 0.0 0.3 0.2 0.0 0.2 0.0 0.0
Effect of Current on Time of Lead Deposition
NO.
Time, hlin. 15 30 45 15 30 45 10 15 30
Current, Amp. 3 3 3
5
7.5 7.5 7.5 10 10
10 15 5
10
Table V.
Taken 0,1026 0.1026 0.1026 0.1026 0.1026 0,1026 0.1026 0.1026 0.1026 0.1026 0.1026 0.1026 0.1026 0 1026 0.1026 0.1026 0.1026 0.1026
4 4 4
: 5
Lead, Gram Taken Found 0.1026 0.1020 0.1026 0.1024 0.1026 0.1026 0.1026 0.1024 0.1026 0.1026 0.1026 0.1026 0.1026 0.1021 0.1026 0.1026 0,1026 0.1026 0,1026 0.1022 0.1026 0.1026 0.1026 0.1026 0.1026 0.1025 0.1026 0.1026
Error, hlg. 0.6 0.2 0.0 0.2 0.0 0.0 0.2 0.0 0.0 0.4 0.0 0.0 0.1 0.0
Interference Studies on Lead Deposition Using Primary Standard Lead Nitrate Interference Amount, mg. Taken Iron 20.0 Arsenic 0.5 1.0 Bismuth 2 0 20
/.o
Barium
10.0 20.0
Lead, Gram Taken Found 0,1004 0.1004 0.1000 0.1000 0.1003 0.0999 0.1004 0.1004 0.1004 0.1007 0 1005 0.0995 0.1003 0.1003 0.1006 0.1003
Error, Mg. 0.0 0.0 0.4 0.0 0.3 1.0 0.0 0.3
PROCEDURE FOR DETERMIYATION OF LEAD IN LEAD SULFIDE ORES
The sample of the ore, containing between 0.1 and 0.15 gram of lead, is weighed out and transferred to a dry 300-ml. tall-form beaker, Approximately 15 ml. of 72% perchloric acid are added and the beaker is swirled to disperse the sample. Glass beads are added to help prevent bumping. The beaker is covered with a watch glass and placed on a Nichrome gauze. Heat is applied with a Tirrill burner adjusted so that it boils 72% perchloric acid very gently. By the time the perchloric acid begins to boil, the sample is in solution, but the solution is allowed to boil very y t l y for about 1 minute to expel any hydrochloric acid formed uring the solution process. The beaker is then cooled for about 2 minutes, and the walls of the beaker are washed don-n with distilled water. The solution is diluted with water to about 50 ml. (about 1 inch in the beaker) and boiled for about 2 minutes to expel chlorine, (This is very essential.) Next, 30 to 35 ml. of concentrated nitric acid are added and the solution j s placed on the deposition apparatus. Distilled water is added until the electrodes are nearly covered (about 125 to 150 ml. total volume). The current used for deposition can vary up to a t least 10 amperes. The length of time required to obtain complete deposition varies inversely with the current used (see Table IV). I t is also important that the solution be stirred during the deposition. (In the analyses that follow, the current was 3 amperes and the time was 1 hour. Stirring was accomplished with a rotating platinum cathode.)
Table VI. Interference Studies on Lead Deposition Using Lead Ore No. 1 SO.
1 2 3
Interference Amount, nig. 0.5 1.0 Antimony 1.0 Taken Arsenic
2.0
4
5 6
7 8 9
10
11 12 13 14 15 16 17 18 19 20 21 22 23
Bismuth
Silver Manganese
Tin Barium
1.0 2.0 j.0 7.0 3.0 4.0 j.0 5.0 0.0 7.0 10.0 3.0 5.0 7.0
5:
10.0 50.0 100.0
Lead, Gram Taken Found 0.1001 0.1001 0.1002 0.0998 0.1000 0.1000 0.1004 0.0999 0.1003 0.1003 0,1005 0.1005 0.1003 0,1000 0.1002 0.0991 0.1003 0.1003 0.1002 0.1000 0,1002 0.0996 0.1001 0.1001 0.1004 0.1005 0.0999 0.1003 0.1000 0.0995 0.1000 0.1001 0.1003 0.1005 0.1003 0.0999 0.1001 0.1001 0.1000 0.1000 0.1002 0.1002 0.1002 0.0952 0,1000 0.0870
Error, LIg. 0.0 0.4 0.0 0.5 0.0 0.0 0.3 1.1 0.0 0.2 0.6 0.0 0.1 0.4 0.5 0.1 0.2 0.4 0.0 0.0 0.0 5.0 13.0
V O L U M E 27, NO. 1 2 , D E C E M B E R 1 9 5 5 Table VII.
Consecutive Analyses of Lead Sulfide Ores
Lead Sulfide Ore
Dev. from
Lead,
%
No. 1 1 2 3
Av.
68.95 68.78 68.83 68.77 68.89 68.90 68.81 68.85 68.85
.4v.
61.80 61.79 61.91 61.84 61.89 61.93 61.96 61.95 61.91
4
5 6 7 8 No. 2 1 3
3 4 5 6
7 b 8
so. 3 1 2 3 4
.4v.
+0.10 -0.07 -0.02 -0.08 -0.04
+0.05 -0.04 io.00
zto.05 -0.11
&O.OO
-0.07 -0.02 +0.02 +0.05 +0.04 10.05
Av.
0.06
Modified Procedure. Arsenic, antimony, and tin that may interfere in the determination of lead (see Table VI) can be removed quantitatively as the volatile bromides (8). This volatilization was used advantageously by Norwitz and Norwitz (6) in the deposition of lead. The following procedure may be used to remove these three interferences. The sample is put into solution as above with 15 ml. of 72% perchloric acid. Following the gentle boiling of the concentrated acid solution, the solution is allowed to cool, 20 ml. of 48% hydrobromic acid are added, and the solution is evaporated on a hot plate to the dense white fumes of perchloric acid. Another 20 ml. of 48% hydrobromic acid are added t o the cooled solution, and the solution again evaporated to fumes of perchloric acid. The solution is boiled gently for 2 minutes to expel the last traces of bromide, after xhich it is cooled for 2 minutes, diluted to about 50 ml. of water, and boiled for about 2 minutes to expel chlorine as in the above detailed procedure. From this point the procedures are identical. This modified procedure adds about an hour to the time required for the determination of lead. RESULTS OF LEAD ORE ANALYSIS
+o.oi
-0.03 t0.03 +0.08 -0.01 -0.08 -0.08 -0.02
44,44
6 7 8
0.062
+0.06
44.43 11.33 44,39
5
Std. Dev.
1975
44,35 44.28 44.28 44.31 44.36
10.05
0.062
No. 3 with 50 mg. of arsenic added (using modified procedure) -0.08 1 44.23 44.29 -0.02 2 41.32 +0.01 3 4 44.40 +0.09 6 44.35 +0.04 44.25 -0.06 -0.06 6 Av. 44.31 f0.05 0.063
Using the above procedure, three different lead ore samples were analyzed (Table VII). Also included in Table VI1 are the results of the determination of sample 3 with 50 mg. of arsenic added using the modified procedure. Though the average ia lower than sample 3 n-ithout the arsenic, the results are within the error of the method. ACKNOWLEDGMENT
The authors are indebted to S. M. Lane of the American Smelting and Refining Co., East Helena, Mont., for the lead sulfide flotation concentrates used in the dissolution studies. LITERATURE CITED
-After deposition is completed, the electrodes are washed with water, and the anode is placed in a 1 5 o - d . beaker containing 25 ml. of water, 0.5 gram of hydroxylammonium chloride, and about 0.25 ml. of concentrated nitric acid. The beaker is tilted sufficiently to allow solution of the lead dioxide. The electrode is washed with rrater and removed. Ten milliliters of 0.2M tartrate solution are added, and 511 sodium hydroxide is added dropn~ise until the precipitate of lead tartrate just dissolves. (-4s the sodium hydroxide is added and the nitric acid neutralized, lead tartrate precipitates. With continued addition of the sodium hydroxide, the lead tartrate redissolves.) Approximately 1 ml. of the pH 10 buffer, about 0.25 gram of sodium cyanide, and 6 drops of 1lanVer indicator are added. The solution is titrated with 0.02W HexaVer until the indicator changes from violet to blue-green.
(1) ~ ~ F., i ~andl mreidenfe1d, , L,, 2. anal. Chem., 84, 220 (1931). (2) Flaschka, H., Mekrochemie Ber Mikrochtm. Acta, 39, 315 (1962). (3) Garcia, Llanuel, Quim. e ind., 9, (1932), (4) Goetz, C. 8 . , and L ~ T, c., ~ Division ~ of Analytical ~ ~ Chem, istry, ACS, Kansas City, Mo., March 1954. ( 5 ) Majdel, J., z, anal. Chem,, 83, 36 (1931), ( 6 ) Nor+itz, G , , and Norwitz, I., lMetallurgia, 46, 318 (1952), (7) Schrenk, w. T.,and Delano, p. H., IsD. ENG, CREM., ANAL. ED.,3, 27 (1931). (8) Smith, G. F., ,,,IIixed Perchloric, Sulfuric and Phosphoric Acids and Their Applications in Analysis,” 2nd ed., p. 61, G . F. Smith Chemical Co., Columbus, Ohio, 1942. RECEIVED for re\iem December 27, 1954. Accepted August 19, 1955. Sixteenth Midwest Regional Meeting, ACS, Omaha, Keh., November 1954.
Determination of Aldehydes Using Unsymmetrical Dimethylhydrazine SIDNEY SlGGlA
and
C. R. STAHL
Central Research Laboratory, G e n e r a l A n i l i n e & Film Corp., Easton, P a .
4 method is presented for determining aldehydes by reaction with unsymmetrical dimethylhydrazine. An excess of hydrazine reagent is added to a sample, and, after the reaction is complete, the excess is titrated with standard acid. Ketones cannot be determined by this method. Aromatic aldehydes can be determined in the presence of ketones, but aliphatic aldehydes cannot. The hydrazine reagent is alkaline and is stable toward decomposition and oxidation, making possible a precision and recovery within &l%.Because the method is nonaqueous in nature, its range is extended beyond just water-soluble samples. Acetals and carboxylic acids do not interfere.
T
HE use of hydrazines for the determination of aldehydes has
been restricted by one or more factors, the most common of which are: ease of oxidation of the hydrazines, use of aqueous reagents limiting analysis to water-soluble samples, and use of hydrazonium salts which are acidic and will react with acetals aa well as aldehydes. Employing dimethylhydrazine makes it possible to overcome these difficulties. Kleber (16) tried the determination of some carbonyl compounds by addition of excess of phenylhydrazine and acidimetric determination of the excess. Phenylhydrazine is a poor reagent, owing to its ease of oxidation by atmospheric oxygen. Blanks can be run to account for the phenylhydrazine lost through oxida-
