V O L U M E 20, N O . 11, N O V E M B E R 1 9 4 8 Table VI. Sample XO.
56a 120
Table \-II. Sample
1055
used in this investigation, thus making it possible to reproduce the new mixed indicator from various batches of these indicators. This research was sponsored by a grant from the Research Fund of the University of Alabama.
Results Obtained with Bureau of Standards Phosphate Rocks
Sample Gram 0.1088 0.1102 0.1100 0.0793 0.0560
PZOS Ce tified 3afalue %
PZOK Exptl.
Fez02 70
AlzOs 70
F-~ %
Si02
%
70
%
32.90 32.90 35.20 35.20 35.20
32.89 32.88 35.18 35.23 35.22
2.18 2.18 0.89 0.89 0.89
2.02 2.02 0.80 0.80 0.80
3.56 3.56 3.76 3.76 3.76
11.01 11.01 7.40 7.40 7.40
0.08 0.08 0.07 0.07 0.07
Value
_____Other ~ Materials _ _Present
Ti02
Synthetic Potassium Acid Phosphate Solutions Containing Impurities P*Osin 25-M1. Aliquot Calcd. Exptl. value
CaO
Fer01
MQ.
MQ.
Gram 0.03
Gram 0.005
0.005
0.1
0.03 0.03 0.06 0.03
0,005 0.010 0.005 0.005
0.005 0.010
0.1
0.005 0.005
0.1
0.03
0.005
0,005
0.1
A
31.18
B
20.92
C
10.10
D
5.53
(1) Assoc. Official Agr. Chem.,
Impurities Present in 25-111. .Iliquot
value
31.14
31.16
20.94 20.95 20.92 10.03 10.12 5.52 5,82
Wash Solution. Either potassium nitrate or cold water may be used for xashing the yellow precipitate. According to Kolthoff and Sandell (5), water peptizes the precipitate and causes it to run through the filter; however, for the volumetric procedure, cold water is recommended (1). Experiments show that identical results are obtained when either potassium nitrate or cold water is used as the wash solution, provided the amount of wash solution when water is used is kept a t a minimum. APPLICATION OF METHOD
A number of synthetic potassium acid phosphate solutions, ranging from 32 to 6.0 mg. of phosphorus pentoxide per 25-ml. aliquot, were analyzed (Tables IV and V). The data show that the results are independent of the amount of phosphorus pentoxide in the sample. The maximum deviation was 0.1 mg. and the average deviation 0.05 mg. of phosphorus pentoxide. Two Bureau of Standards samples of phosphate rock were analyzed, along with several synthetic solutions that contained certain impurities (Tables VI and 1’11). ACKNOWLEDGMENTS
The authors are indebted to the Eastman Kodak Company, Rochester, S . Y., for standardizing the purity of the indicators
-41~0s Gram
H~SOI Gram
... ...
LITERATURE CITED
MnO Gram ,..
0.OOSo 0.0005
Official and Tentative Methods of Analysis. 5th ed., p. 23 (1940). (2) Graftiau, F., Atti V I Congr. intern. chim. applicata, Rome, 1, 64 (1906).
W. F., and Lundell, G. E. F., “Applied Inorganic Analysis,” p. 563, New York, John Wiley & Sons, 1929. (4) Ibid.,p. 568. (5) Kolthoff, I. M., and Sandell, E B., “Textbook of Quantitative Inarganic Analysis,” p. 371, New York, Macmillan Co., 1937. (6) Lipowitz, Pogg. Ann., 119, 135 (1860). (7) Lundell, G. E. F., and Hoffman, J. I., “Outlines of Methods of Chemical Analysis,” p. 46, New York, John Wiley & Sons, I
.
.
...
(3) Hillebrand,
1938. ENG. (8) MacIntire, W. H., Shaw, W. M., and Hardin, L. J., IND. CHEM.,AXAL.ED.,10, 143 (1938). (9) Pauling, L., J. Am. Chem. Soc., 51, 2863 (1929). (10) Pellet,,H., Bull. assoe. belge chim., 3, 51 (1888-89). (11) Smith, G. F., “Pzrchloric Acid,” 4th ed., Columbus, Ohio, G Frederick Smith Chemical Co., 1940. (12) Vincent, V.,Ann. fals., 23, 475 (1930). (13) Wiley, H . W., “Principles and Practice of -4grioultural Analysis, Vol. 11, Fertilizers and Insecticidea,” 3rd ed., p. 63, Table VII, Easton, Pa., Chemical Publishing Co., 1931. (14) Ibid., p. 186. 42, 2208 (15) Willard, H. H., and Cake, W. E., J. Am. Chem. SOC., (1920). (16) Willard, H. H., and Diehl, Harvey, “Advanced Quantitative Analysis,” p. 8, New York, D. Van Nostrand Co., 1943. RECEIVED October 4, 1947. Presented before the Division of Physical and CHEMICAL Inorganic Chemistry, at the 100th Meeting of the AMERICAN SOCIETY, Detroit, Mich. Report on citromolybdate aolution presented before the Division of Physical and Inorganic Chemistry, at the lOlst meeting of the AMERICAN CHEMICAL SOCIETY, St. Louis, AVO.A part of this work was presented by Howard P. Crammer in partial fulfillment of the reqoirements for the degree of master of science, 1941.
CHEMISTRY OF THORIUM Quantitative Estimation of Thorium by a Titrimetric Iodate Procedure THERALD MOELLER AND NANCY DOWNS FRITZ, University of IEZirwis, Urbana, I l l .
T
HE lack of rapid methods for the accurate estimation of thorium in the presence of yttrium and the rare earth elements has been emphasized repeatedly (1, 5, 8). Of the recorded reactions of the thorium ion, that involving its precipitation as iodate from solutions containing nitric acid appears most promising as a basis for a direct and potentially rapid method for estimating the element under these conditions. Not only does this reaction yield a thorium salt containing an ion that may be determined by familiar oxidimetric procedures, but i t also effects complete separation of thorium from yttrium and the tripositive rare earth
elements, the iodates of which are soluble in nitric acid solutions (6).
While iodate precipitation is an established procedure for freeing thorium of yttrium and the rare earth elements prior to its estimation by gravimetric means ( 8 ) , reports on its adaptation to a direct titrimetric method have been fragmentary. Chernikhov and Uspenskaya (5)described a procedure in which thorium was precipitated from nitric acid solution by excess potassium iodate, and the precipitate was washed with nitric acid containing potassium iodate, treated with 95% ethanol, dried, and dissolved in
A N A L Y T I C A L CHEMISTRY
1056
Separation of thorium from yttrium and the rare earth elements by precipitation as the iodate from solutions containing considerable quantities of nitric acid has been extended to titrimetric estimation of thorium through iodometric determination of the iodate content of the precipitate. By this means, some 99% of the thorium in a pure salt solution, in a synthetic mixture containing yttrium and the rare earth elements, or in a natural monazite sand may be estimated rapidly and with excellent precision. Although lacking in abselute accuracy, the procedure gives results comparable with those obtained by accepted procedures and is much more rapid. Lack of absolute quantitative character apparently stems from the impossibilitl- of freeing precipitated thorium iodate from adsorbed iodate and nitrate without some loss because of dissolution and hj-drolysis.
acidified potassium iodide solution. Titration of the liberated iodine with thiosulfate gave the thorium content based upon the composition 4Th(103)a.K103.18H20 as characterizing the precipitate. An alternative approach, based upon treatment of a slightly acidic thorium salt solution with excess standard potassiumiodate solution and determination of the excess after filtration by addition of acid and iodide and potentiometric titration using standard thiosulfate solution, has been proposed by Spacu and Spacu (9). Except for some measurements in the presence of cerium (S), no attempt has been made to extend these procedures to systems containing yttrium and the rare earth elements. Direct application of the method of Spacu and Spacu to such systems appears unlikely because of the apparent impossibility of preventing precipitation of the iodates of yttrium and the rare earth elements while maintaining the nitric acid concentration a t a sufficiently low level to avoid interference with the iodometric procedure (7'). The method of Chernikhov and Uspenskaya offers more promise, but the data given by these authors are insufficient to permit direct extension of their procedure. Chernikhov and Uspenskaya limited their investigations to pure thorium salt solutions containing the equivalent of 0.08 to 16 mg. of the element and to thorium-cerium combinations in which the thorium concentrations were within this same range. Inasmuch as their reported errors of 6 to 7% a t low concentrations were reduced to some 370 in the range of 4 to 16 mg. of thorium, it would appear that perhaps an even greater accuracy would characterize determinations a t still higher concentrations where the method should be most useful. However, as these errors were somewhat higher, on the average, in the presence of cerium, the utility of the method as applied to materials containing the rare earth elements might be questioned. The lack of specificity in experimental directions and the unusual composition reported for the precipitate also suggest further study of the Chernikhov and Uspenskaya procedure. Accordingly, a number of phases of the method have been examined, and the modified procedure which resulted is offered here as an extremely rapid method for estimating thorium in the presence of yttrium and the rare earth elements. MATERIALS
All thorium salt solutions used were prepared from a sample of chemically pure thorium nitrate tetrahydrate obtained from the Lindsay Light and Chemical Company. This material gave no evidence of the presence of yttrium and the rare earth elements. Rare earth materials used were obtained from the stocks accumulated a t the University of Illinois. Other chemicals, including cerium (IV) ammonium nitrate, were of analytical reagent quality and were used without further purification. Samples of monazite sands used for analysis were provided by the Lindsay Light and Chemical Company. Thorium salt solutions were standardized by precipitating aliquots with ammonia, washing, igniting, and weighing as thorium dioxide (8). Potassium iodate solutions Fere prepared directly from the pure dry salt, Sodium thiosulfate solutions were standardized against potassium iodate by the usual iodide procedure.
C03IPOSITION OF THE PRECIPITATE
The composition 4Th(I03)~.K103.18H20 reported by Chernikhov and Uspenskaya (3) would indicate a ratio of 4.25 moles of iodate to 1 of thorium in the precipitated product. Because of the some!\ hat unusual nature of this formulation and because of the bearing which the ratio of iodate to thorium v, ould have upon the analytical results, some preliminary analyses of thorium iodate samples prepared under a variety of conditions were made. Iodate was determined in these samples by dissolution of the weighed material in 4 S sulfuric acid, addition of excess 10% potassium iodide solution, and titration of the liberated iodine with standard sodium thiosulfate solution. After titration, thorium was recovered from these solutions by precipitation with aqueous ammonla. Such precipitates were then dissolved in hydrochloric acid solution and thorium was determined by precipitation with ammonia and ignition to weighable oxide. ' For a sample of thorium iodate precipitated with 0.2 M potassium iodate solution from a solution 0.2 S in nitric acid, the mole ratio of iodate to thorium was 3.99 to 1. For a sample of thorium iodate precipitated by a solution containing 15 grams of potassium iodate in 50 ml. of concentrated nitric acid and 30 ml. of water ( 6 ) , this mole ratio was 4.10 to 1. In no instance did the ratio exceed 4.10 t o 1, and it averaged 4.02 to 1. One must conclude, therefore, that regardless of the over-all composition of the precipitate, iodate and thorium are present in the ratio corresponding to that in the pure compound Th(IO3)r. Excessive washing of the thorium iodate precipitates not only caused appreciable dissolution but also dropped the ratio of iodate to thorium toas low as 3.7 to 1,probably because ofpartial hydrolysis. CONDITIONS NECESSARY FOR FORMATION, WASHING, AND DISSOLUTION OF PRECIPITATE
Although preliminary studies showed thorium to be completely precipitated by 0.1 M potassium iodate solution over a nitric acid concentration range of 0.02 to 1.60 N , the rare earth elements were also a t least partially precipitated under these conditions. Subsequent studies confirmed the observations of hleyer and Speter (8) relative to completeness of precipitation and separation from the rare earth elements a t higher nitric acid concentrations, providing excess iodate is present. The recommended quantity ( 6 )of 15 grams of potassium iodate dissolved in 50 ml. of concentrated (specific gravity 1.42) nitric acid and 30 ml. of water per 100 ml. of solution containing 100 to 200 mg. of thorium was found eminently satisfactory and m-as used consistently in the remainder of the work. Separation from ytt,rium and the tripositive rare earth elements was ordinarily complete in one operation. HoTever, double precipitation is often desirable if the quantities of these elements are comparatively large. Thorium iodate precipitated under these conditions is often too finely divided to be removed directly by filtration. Sufficient agglomeration to permit retention of the precipitated particles by filter paper may be effected by either a 2-hour period of digestion
V O L U M E 20, NO. 11, NOVEMBER 1 9 4 8
1057
on the steam bath or frequent stirring a t room temperature over a 30-minute period. Because prolonged digestion often renders such precipitates difficult to dissolve in acid, the latter procedure is preferred. Separation by centrifuging was inefficient because of the tendency of the precipitate to adhere to the containers. Washing precipitated thorium iodate with a solution of potassium iodate in nitric acid (6) effectively removes adsorbed yttrium and rare earth materials without effecting decomposition or dissolution of the precipitation. The removal of adhering iodate and nitrate after this operation is essential to the accuracy of the titrimetric determination, but i t is complicated by the measurable hydrolysis of thorium iodate and by the appreciable solubility of the compound in water (varying, as roughly determined in this investigation, from 13.8 mg. per 100 ml. of water a t 0" C. to 66 mg. a t 100" C.). Chernikhov and Uspenskaya ( 3 ) are extremely indefinite as to this point, and the treatment with 95% ethanol which they recommend does little if anything to remove excess potassium iodate because of the limited solubility of this salt in alcohol. Methanol and acetone were found to be equally ineffective as wash liquids. Sulfuric acid solutions cannot be used a t concentrations above 0.005 N because of solvent effects, while a t lower concentrations they offer no advantages over water alone. Ammonium nitrate and chloride solutions peptized thorium iodate and could not be used satisfactorily. As a result of these studies, water rvas selected as the most suitable wash liquid. A series of aliquots of a standard thorium nitrate solution containing the equivalent of 8.17 mg. of thorium dioxide per millliter was precipitated a t room temperature with 10 to 20-ml. portions of the potassium iodate-nitric acid reagent described above. In each case, the precipitated thorium iodate was removed and washed on the filter paper with 20 ml. of a solution containing 2 grams of potassium iodate in 50 ml. of diluted (specific gravity 1.2) nitric acid and 200 ml. of water. Washing was then completed Tyith distilled water, the quantity and temperature being varied from one set of samples to another. The precipitates were dissolved in 4 N sulfuric acid solution, excess 10% potassium iodide solution was added, and the liberated iodine was titrated with standard 0.2 Y sodium thiosulfate solution. The thorium recoveries, as calculated from the ratio of 4103- to 1Thf4, were then compared with the original quantity of thorium taken. Data so obtained showed the thorium recovery to decrease with increase in the temperature and volume of the wash water. However, if the washing were effected with ice water in the amount of 75 to 100 ml. for each 100 to 200 mg. of thorium, complete removal of adsorbed iodate and recovery of an average of approximately 99% of the thorium R-ere effected That absolutely
Table I.
E s t i m a t i o n of T h o r i u m in Presence of Y t t r i u m a n d Rare E a r t h E l e m e n t s
.
Material Added Oxide
ThOz Taken
ThOz Found
Thorium Recovery
Ndz03n
435.3 290.2 290.2
141.0 141 .O 141 .O
142.1 141.5 140.2
100.7 100.3 99.4
CeOn b
344.0 344.0 344.0 344.0 172,O 172.0
176.3 176.3 176.3 176.3 176.3 176.3
175.0 175.0 173.0 173.0 173.0 171 .O
99.3 99.3 98.1 98.1 98.1 97.0
Added as Kd(X0a)s. Free from other rare earths. Added as Ce(K'Oa)r.ZNH4?jOs. llnalytical reagent quality. Added as mixed yttrium and yttrium group chlorides. Average atomic weight 120.3. a
b
quantitative recovery was never attained is due undoubtedly to the dissolution and hydrolysis effects mentioned. The most suitable solvent for precipitated thorium iodate is 4 iV sulfuric acid. This material works efficiently and causes no interference with the procedure through liberation of excess iodine. Hydrochloric and nitric acids cannot be used for this reason. Best results were obtained when the filter paper containing the precipitate was transferred directly to the titration flask for treatment with sulfuric acid solution. ESTIMATIOY OF THORIUM 13' PRESENCE OF YTTRIUM A N D CERTAIN RARE EARTH ELEMENTS
The generally favorable results obtained with pure thorium salt solutions prompted extension of the method as described to thorium estimation in the presence of yttrium and the rare earth elements. Determinations were made in the presence of individual members of the cerium group and of mixtures of yttrium group elements. Special emphasis was placed upon analyses in the presence of cerium (IV) because of the chemical similarities between compounds of this material and those of thorium. To a 100-ml. sample containing the equivalent of approximately 175 mg. of Tho., 50 ml. of concentrated (specific gravity 1.42) nitric acid are added. If cerium (IV) is present, a few drops of 30% hydrogen peroxide are added, and the excess is removed by boiling. To the cooled solution, 15 grams of potassium iodate dissolved in 50 ml. of concentrated nitric acid and 30 ml. of water are added. The resulting suspension is alloved to stand for 0.5 hour with frequent stirring. The white precipitate of thorium iodate is then removed by filtration through a b7hatman No. 50 paper and is washed on the paper with 20 ml. of a solution containing 2 grams of potassium iodate in 25 ml. of concentrated nitric acid and 225 ml. of mater. The precipitate is then washed into the original precipitation beaker with hot mater. The suspension is heated to boiling, and 30 ml. of concentrated nitric acid are added with constant stirring to dissolve the precipitate. The solution is allowed to cool to room temperature, and the thorium is reprecipitated by the addition of 4 grams of potassium iodate dissolved in 7 ml. of concentrated nitric acid and 20 ml. of water. The suspension is filtered through the original filter paper and the precipitate allowed t o drain and then washed on the filter with not more than 100 ml. of ice water, added in small portions. The filter paper containing the precipitate is transferred to a 500-ml. Erlenmeyer fla-k and the sample is dissolved in 100 nil. of 4 iV sulfuric acid solution. .Ibout 50 ml. of xater and 30 to 35 ml. of 10% potassium iodide are added, and the liberated iodine is titrated immediately with standard 0.2 N sodium thiosulfate solution to the starch end point. The thorium dioxide (or thorium) content is then calculated on the basis of the ratio 4IOj- to l T h - + * + . Data in Table I summarize results obtained for a number of typical synthetic mixtures. iilthough the thorium recoveries are not quantitative, they deviate but little from the true values, and the percentage errors are small. The method is applicable, therefore, under the conditions outlined. DIRECT ESTI\I4TIOY OF THORIUM 1Y MOYAZITE SANDS
The method was then extended to determination of thorium in monazite sand concentrates. The follon-ing procedure is recommended as the result of many analyses:
h 10- to 20-gram sample of screened (100-mesh) monazite sand concentrate is added to concentrated sulfuric acid which has been evaporatcd to sulfur triovide fumes. The mixture is boiled until the sand has completely disintegrated, and the resulting pasty mass is cooled to room temperature. Crushed ice is added directly to the mass, and when the ice has melted, the suspension is filtered through a Buchner funnel with filter paper pulp added as a filter aid. The residue on the paper is washed with mater and the combined filtrate and washings are diluted to 500 ml. in a volumetric flask. For analysis, an aliquot of this solution corresponding to 1 to 2.5 grams of the original sand is diluted to 100 ml. and treated exactly as outlined for the estimation of thorium in the presence of the rare earth elements. Reduction with hydrogen peroxide is recommended for all samples as a precautionary measure to prevent interference by cerium (IW.
ANALYTICAL CHEMISTRY
1058 Table 11.
Estimation of Thorium in Monazite Sands
Monazite Designation Source Travancore U-1 Travancore u-2 Brazil u-3 Brazil u-4 Travancore u-5 Bra$ U-6 v-1 1 v-2 ? v-3 Brazil Brazil Travancore
Per Cent ThOz (Average) kolumetric Iodate 2 precipitation tations Hexamine 9.33 9.87 9.93 9.15 9.13 9.21 6.31 6.09 LBO 5.97 5.95 8171 8.66 8.88 6.13 5.99 6.07 8.75 8.68 5.77 6.07 8.62 8.90 5.99 6.54 6.35 6.43 8.84 8.90
1 precipi-
cases. The accuracy of the iodate procedure so demonstrated is supported by the fact that data may be obtained with it in less than 8 hours as compared with the 2 days required for the hexamine. The pyrophosphate procedure of Carney and C a m p bell ( 2 ) is even more time-consuming. ACKNOWLEDGMENT
The authors wish to express their appreciation to the Office of Naval Research for support received during this investigation. LITERATURE CITED
Banks, C. V., and Diehl, H., ANAL.CHEM.,19, 222 (1947). Carney, R. J., andcampbell, E. D., J. Am. Chem. SOC.,36, 1134 ( 19 14).
Average results obtained for a number of monazite sands of varying thorium contents are summarized in Table 11. Data for both single and double iodate precipitatims are included for certain samples for purposes of comparison. Included also are data for the same samples as obtained by the hexamethylenetetramine (hexamine) procedure of Ismail and Harwood (4),which yields quantitative results but is excessively tedious because of the multiple precipitations required for clean separations. Data obtained by the volumetric iodate procedure do not check the hexamine data exactly, but the agreement is very good in almost all
Chernikhov, Yu. A., and Uspenskaya, T. A . , Zavodslzaya Lab., 9, 276 (1940).
Ismail, A. M., and Harwood, H. F., Analyst, 62, 185 (1937). Justel, B., Die Chemie, 56, 157 (1943). Meyer, R. J., and Speter, M., Chem.-Ztg., 34, 306 (1910). Moeller, T., and Fritz, N. D., SCI.Rept. N6ori-71, T.O. VII, University of Illinois, Jan. 23, 1948. Moeller, T., Schweitzer, G. K., and Starr, D. D., Chem. Rev.,42, 63 (1948).
Spacu, G., and Spacu, P., Bull. Sect. sci. acad. romaine, 26, 295 (1945)
I
RECEIVED December 26,
1947.
Quantitative Determination of Hydrazine R. A. PENNEMAN AND L. F. AUDRIETH, University of Illinois, Urbana, Ill. Methods recorded in the literature for the quantitative determination of hydrazine were surveyed and those which promised both speed and accuracy were studied experimentally during the analysis of hundreds of hydrazine samples. Excellent and reproducible results were obtained using either the direct iodine or the direct iodate method with solvent or with indicator. The direct acid titration of free hydrazine with 0.5 N hydrochloric acid to either the methyl red or methyl orange end point, followed by
I
N COKNECTION with studies involving the chemistry of
hydrazine, the need for a rapid and convenient method for the quantitative determination of the free base made it necessary to check recorded procedures experimentally, especially because no summary of methods had appeared in the literature since 1924 (1,9). Procedures for quantitative determination of hydrazine are based on its behavior either as a weak base or as a reducing agent. Consequently, available methods involve either direct titration with standard acids (6, 14) or oxidation to nitrogen by such oxidants as iodine (1, 9 ) , bromine (f), permanganate (9), bromate (9, 10,f6),iodate (9, IS),ferricyanide ( 5 ) ,chloramine (fd), or hypochlorous acid (1). Both types of procedures must be carried out under carefully controlled conditions if accuracy and reproducibility are to be achieved, first, because hydrazonium hydroxide is a weak base (Ka = 8.5 X lo-') and secondly, because oxidation often leads to formation of appreciable quantities of ammonia and hydrazoic acid, in addition to nitrogen ( 3 ) . Methods which make use of iodine, iodate, and permanganate may involve direct titration or these reagents may be used to effect oxidation of hydrazine, followed by determination of a product of the reaction or of the excess of standard oxidant. The ferricyanide procedure is likewise an indirect method in which the ferrocyanide equivalent to hydrazine is determined ceriometrically.
iodate oxidation, is a useful combination where ammonia and/or other basic constituents are also present. The use of micropipets is recommended for the analysis of concentrated hydrazine solutions. Prompt acidification of hydrazine samples prior to analysis avoids absorption of carbon dioxide or moisture or loss of hydrazine by air oxidation. Because of oxidation of free hydrazine by atmospheric oxygen, methods involving the determination of hydrazine in alkaline solution are not recommended.
Inasmuch as a direct titration is better in principle, and more convenient where analyses must be made frequently, the indirect iodate (f), iodine (f), and ferricyanide (5) methods were not checked, even though excellent accuracy is claimed for them (1, 9). The bromine and hypochlorous acid methods were not evaluated, because the reagents are of an objectionable nature. Because of the similarity between the iodate and the bromate methods, the latter was not checked. The experience gained through hundreds of analyses has shown that the direct iodate procedure and a combination acid-iodate method developed by the authors are the most suitable, especially where solutions containing free hydrazine are to be analyzed. The latter procedure was found especially useful where ammonia or some other base is present in solutions containing hydrazine. RECOMMENDED TECHNIQUES FOR HANDLING HYDRAZINE SOLUTIONS
As solutions containing hydrazine are subject to oxidation bg atmospheric oxygen (1-4, '7, f4), fume badly, and absorb carbon dioxide, weight burets or especially constructed pipets should be usled for all sample weighings. The hydrazine should be added to water containing a slight excess of acid, followed by dilution in avolumetric flask to approximately 0.025 M . Where iodate oxidation is to follow, hydrochloric acid should be used. Such acid solutions are stable indefinitely.
