- Email: [email protected]
Precipitation of lead sulphate from homogeneous solution by hydrolysis of sulphamic acid
Short communications
297
REFERENCES 1 A. R. Vasudeva Murthy and B. Sanjiva Rao, Proc. Indian Acad. Sci., 1952,35A, 7. 1 E. Bishop and V. J. Jennings, Talanra, 1958,1,197. * B. Sanjiva Rao, Proc. Indian Acad. Sot., 1939,10,423. ’ B. Sanjiva Rao and M. R. A. R,ao, 10th ZnternaIional Congress of Ckernistry, 1938,3,462. 6 M. R. A. Rao, Proc. Indian Acod. Sci., 1940,11,162.
Precipitation of lead sulphate from homogeneous solution by hydrolysis of snlphamic acid (Received 10 June 1964. Accepted 6 December 1964)
THEtechnique and advantages of precipitation from homogeneous solution have been amply presented by Gordon, Salutsky and Willard.’ They also reviewed the methods that have been employed to generate sulphate ions for the determination of barium, calcium, strontium and lead. Elving and Zook’ precipitated lead sulphate by hydrolysis of dimethyl sulphate in 70-80x methanol. Satisfactory accuracy and precision were obtained for amounts of lead in the range of 10 to 100 mg, except in the presence of large amounts of iron(II1) and aluminium(II1). The conditions under which small quantities of lead are precipitated arc somewhat stringent. The concentration of the methanol, amount of dimethyl sulphate added and digestion t‘ime required are dependent upon the quantities of lead and foreign ions present. There is also a tendency for the precipitate to “creep.” Jamagin and Kenneth precipitated lead sulphate by hydrolysis of sulphamic acid catalyzed by the presence of potassium chlorate. A small-sized, uniform precipitate was formed, the volume of which was measured after centrifugation. The successful use of the hydrol sis of sulphamic acid for the precipitation of barium sulphate *s6led to the present investigation oP the precipitation of lead sulphate by a similar procedure. EXPERIMENTAL All reagents met American Chemical Society specifications of purity. Stdek solutions of lead nitrate. Prepared by dissolving the reagent in distilled water. Definite, volumes of these solutions, measured by means of pipettes, were used in subsequent analyses. The quantity of lead present in the solution delivered by a given pipette was determined by evaporating the solution with an excess of sulphuric acid in a platinum dish. The lead sulphate thus obtained was ignited to constant weight in an electric muflle furnace at 550-600”. Stock solutions of possible interfering ions were prepared by dissolving the corresponding salts in distilled water. National Bureau of Standards copper-base alloys were aqalysed to check the analytical procedure. Apparatus Filtering media. Both porcelain filtering crucibles (Coors, fine porosity) and filter paper were used
successfully for the filtration. Some difficulty was encountered in bringing the porous porcelain crucibles to constant weight if the excess sulphuric acid solution was not removed by a final wash with ethyl alcohol. With either medium, the precipitate was ignited to constant weight in-an electric muffle furnace at 550-600”. Preliminary experiments
Preliminary tests were made to determine the optimum conditions necessary to effect complete precipitation of the lead sulphate. For these tests, 25 ml of lead nitrate stock solution containing approximately 100 mg of lead ion were ipetted into 250-ml beakers. A weighed portion of reagent grade sulphamic acid and suIEcient disti Eed water to give a solution volume of 100 ml were added to each sample. These solutions were heated to incipient boiling for varying times up to 2 hr. Portions of the supematant liquid were tested for completeness of precipitation by adding dilute sulphuric acid. Optimum conditions were obtained when 2 g of sulphamic acid were added to the solutions and the period of heating was 1 hr. The use of O-5- and l-g portions of sulphamic acid gave results which were sli htly low. The heating time and temperature were more critical than the amount of sulphamic acl*d.
298
Short communications
In the analysis of many materials containing lead, such as brass and other alloys, the sample is dissolved in nitric acid. After the removal of tin, frequently the solution is evaporated almost to dryness to remove the excess nitric acid, either before or after the addition of sulphuric acid. In the I, sulphamic acid procedure, if nitric acid is present, sulphate ions are produced homogeneously by the following reaction in addition to the hydrolysis reaction: NHISOII- + NOs- -+ SO,*- + N1O + H*O. TABLE I.-DETERMINATION
Cation added, mg
_
None
Taken 10.6
ii%
Av. None
99.7
Av.
WY
Al(II1) 100
99.7 9R
Av. AI
10
Av. Al(W) 10
Av. Cu(II) 100
Av. Cu(I1) 10
99.2
9= 11.7
ii? 99.7
Gi 99.2
Av.
99.2
Cu(II) 10
10.6
Av.
m
Fe(W) 100
99.7
Av.
W7
Fe(II1) 10
99.2
Av.
OF LEAD IN PRESENCE OF FOREIGN CATIONS
Lead, mg Found Error
Cation added, W
Taken 99.7
10.7 10.5 10.7 10.6
+01 -0.1 so.1 0.0
Mn(II) 100
99.8 99.9 99.8 998
$01 $02 +01 Gi
Av.
99.8 99.5 99%
+@l -0.2 -0.1
98.7 99.1 99.9 -_ 99.2
-0.5 -0.1 +07 0.0
11.5 11.9 11.8 li
--02 +02 $0.1 0.0
99.8 99.8 99.7 !%G
$01 +0*1 0.0 +0*1
99.1 99.0 98.9 %G
-O*l -0.2 -0.3 -0.2
10.2 10.3 IG?
-0.4 -0.3 -_.__ -0.4
99.8 99.8 100.4 1BiI
+0*1 +0*1 +0*7 $0.3
99.1 99.3 99.0 99.1
-0.1 so.1 -0.2 -0.1
9m
Mn(II) 10
99.2
Av.
!%G
Mn(lI) 10
106
Av.
iG%
Ni(II) 100
99.7
Av.
99.7
Ni(II) 10
Av. Ni(I1) 10
99.2
9!z 11.7
Av.
11.7
Zn(I1) 100
99.7
Av. Zn(II) 10
Av. Zn(II) 10
W 99.2
9X 10.6
Lead, mg Found Error 99.0 99.4 99.7 99.9 99.7 9%
-0.7 -0.3
99.4 99.4 99.2 _99.3
+0.2 +0.2 0.0 +0*1
10.4 10.3 10.8 iiG
-0.2 -0.3 +0*2 -0.1
99.8 99.5 99.5 99.6
to.1 -0.2 -0.2 -0.1
99.4 99.2 99.3 9!G
$0.2 0.0 so.1 +0*1
11.6 11.6 11.6 -. 11.6
-0.1 -0.1 -0.1 -0.1
99.9 99.9 99.9 99.9
+0.2 $0.2 +0.2 +0*2
99.4 99.4 99.2 99.3
+0*2 $0.2 0.0 +0*1
t-X.: 0.0 -0.2
10.2 -0.4 10.4 -0.2 10.6 0.0 Av. 10.6 104 -0.2 Mean deviation of all results: 0.18 mg
Short communications Thus, in the procedure the nitric acid.
developed,
299
the sulphamic acid was added before the evaporation
to remove
Procedure The following procedure is based on the preliminary investigations. Acidify the solution, containing up to 100 mg of lead ion, with 10 ml of dilute nitric acid, or use the filtrate from the tin determination of a copper-base alloy. Dilute to approximately 50 ml and add 2 g of solid sulphamic acid. Cover the beaker with a raised watch glass and heat on an electric hot plate at incipient boiling until the volume is reduced to 2-5 ml. Add 25 ml of water and digest for 30 min on a hot-plate or steam-bath. Cool to room temperature and filter, using a weighed porcelain filtering crucible or ashless filter paper. Wash the precipitate five times with 1: 20 sulphuric acid, then five times with small portions of 50% ethyl alcohol to remove traces of sulphuric acid. Ignite the precipitate to constant weight in an electric muffle furnace at 550-600”. TABLE II.-DETERMINATION
Standard
OF EAD IN NATIONAL BUREAU COPPER-BASE ALLOYS
OF STANDARDS
Sample No. 37 Sheet Brass
Composition
%”
Lead found, %
Error, %
Lead (as sulphate) Lead (as oxide) Copper Iron Nickel Tin Zinc
0.964 0.989 70.290 0.290 0.520 1.013 26.890
0.952 0941 0.930
-0.012 -0G23 -0.034
0941 0*007
-0.023
Lead found, %
Error, %
Mean Mean deviation
Standard Composition
%’
Lead Antimony Copper
1.52 0.16 88.33
Iron Nickel Tin Zinc
0.12 0.13 790 1.89 Standard
Composition Lead Aluminium Antimony Arsenic Copper Iron Nickel Phosphorus Sulfur Tin Zinc
Sample No. 52 Cast Bronze
150 -1.49
-0.02 -0.03
1.50 0.005
-0.02
. Mean Mean deviation
Sample No. 63 Phosphor
Bronze Bearing Metal
%”
Lead found, %
9.74 0.05 0.55 0.09
9.67 9.71 964 -
-0.07 -0.03 -0.10
0.02 967
-007
78.05 027 z8
Mean deviation
Error, %
z:: 048
a National Bureau of Standards Analyses. Interferences In order to study the effect of foreign cations on the determination of lead b the foregoing method, a series of tests was conducted in which 10 or 100 mg of the cation were a L!ded to the lead nitrate solution before the addition of sulphamic acid. The cations employed in this study were those which are most commonly encountered m the analysis of lead alloys.
Short communications
300
Table I shows the results of these analyses. The pmsence of the foreign cations listed in the table does not appear to have any effect on-the determhration of lead by thd method. Several determinations were made in which the preci itation was accomplished in a 50% ethyl alcohol solvent. Comparable results were obtained, but Pore&n cations at high concentrations were partially precipitated as the sulphates. Analysis of standard samples Results of the analysis of National Bureau of Standards copper-base alloys by the sulphamic acid procedure are given in Table II. A l-g sample of alloy was dissolved in dilute nitric acid. Insoluble oxides were removed by filtration following the evaporation of the solution almost to dryness and redissolving the soluble nitrates. The filtrate was then analysed for lead by the foregoing procedure.
DISCUSSION The determination of lead as the sulphate can be accomplished b generation of the sulphate ion homogeneously in solution by the slow hydrolysis and oxidation orysulphamic acid in an aqueousnitric acid solution. Excellent results were obtained in the anal&s of samoles containine 10-100 ma of lead. Coarse, well-formed crystals of lead sulphate are prod&d which &e readily tran;ferred fro; the reaction beaker to the filter. Troublesome %reeping” of the precipitate does not occur and the lead sulphate is easily washed free from adsorbed ions. Photomicrographs in Figs. l-3 show that there is little, if any, difference in the size of crystals of lead sulphate produced by the ordinary sulphuric acid method and by the homogeneous precipitation methods in alcohol-water solutions using dimethyl sulphate or sulphamic acid. Fig. 4 shows the remarkable increase in sire and regularity of the shape of the crystals of lead sulphate formed by homogeneous precipitation with sulphamic acid in aqueous solution. The crystals produced by the sulphuric acid procedure are more needle-shaped than those formed by homogeneous precipitation. All photographs are at the same magnification. As shown in Table I, the average deviation of all results from the true value was @18mg. This average deviation did not vary signdlcantly with either the amount of lead taken or the amount of foreign cation present. The accuracy and precision of the method for the analysis of three National Bureau of Standards cop r-base alloys are given in Table II. The method is believed to be superior to the other methods p” or the gravimetric determination of lead as the sulphate, in that the conditions for quantitative precipitation are less stringent. Acknowle&ement-The authors wish to express their appreciation to Dr. 0. F. Edwards, Department tals and to the National Science of Microbiology, for the photomicrographs of the lead sulphate Foundation for partial support of the project by a grant fromciKs t e Undergraduate Research Participation Programme. Department of Chemistry University of Kentucky Lexington, Kentucky, U.S.A.
J. E. KOLES P. A. SHINNERS W. F. WAGNER+
Summary-The determination of lead as the sulphate is accomplished by generation of the sulphate ion homogeneously from the slow hydrolysis and oxidation of sulphamic acid in an aqueous-nitric acid solution. Samples containing 10-100 mg of lead from copper-base alloys or solutions containing varying amounts of aluminium(I11). copper(H), iron(II1). manganese(H), nickel0 and zinc@) ions have been analysed successfully. Coarse, well-formed crystals are obtained, which filter easily. Zusanunenfassuag-Die Bleibestimmung als Bleisulfat wurde so durchgefilhrt, daB das Sulfat homogen durch langsame Hydrolyse und Oxydation von Amidosulfont&ure in w&&iger, salpetersaurer Losung erxeugt wurde. Proben mit 10-100 mg Blei aus Legierungen auf Kupfergrundlage oder aus Liisungen mit wechselnden Mengen Al(III), Cu(II), Fe(W), Mn(II), Ni(II) und Zn(II) wurden mit Erfolg analysiert. Grobe, gut ausgebildete Kristalle wurdqn erhalten, die sich leicht flltrieren l&en. l
To whom correspondence concerning this work should be sent.
FIG. 1.-Lead
FIG. 2.-Lead
sulphate precipitated by conventional sulphuric acid method.
sulphate precipitated from homogeneous solution by hydrolysis of dhnethyl sulphate.
300
FIG. 3.-Lead
sulphate precipitated from homogeneous solution by hydrolysis of sulphamic acid in 50 % ethanol.
FIG. 4.-Lead
sulphate precipitated from homoge?eous solution by hydrolysis of sulphamic acid in water.
Short communications
301
R&rum-n a dose le plomb a Petat de sulfate en g&&ant l’ion sulfate en milieu homogene par hydrolyse lente et oxyda@nt de l’acide sulfamique en solution eau-acide nitrique. On aanalysc avec succ&sde.sBchantillons d’alliages base de cuivre contenant 10 a 100 mg de plomb, ou des solutions contenant des quantites variables de Al(III), Cu(II), Fe(‘lII), Mn(II), Ni(I1) et Zn(II). On obtient de gros cristaux bien form&s, aisement filterables. REFERENCES 1 L. Cordon, M. L. Salutsky and H. H. Willard, Precipitation from Homogeneous Solution. John Wilev and Sons, Inc., New York, 1959. * P. J.~Elving and W. C. Zook, Anily$. Chem., 1953,25,502. ’ R. C. Jarnaain and C. T. Kenner. ibid.. 1952.24.2016. 4 W. F. Wag& and J. A. Wuellner, ibid:, 1952,24, 1013. 6 L. Cordon and L. Rowley, ibid., 1957,29,34.
297
REFERENCES 1 A. R. Vasudeva Murthy and B. Sanjiva Rao, Proc. Indian Acad. Sci., 1952,35A, 7. 1 E. Bishop and V. J. Jennings, Talanra, 1958,1,197. * B. Sanjiva Rao, Proc. Indian Acad. Sot., 1939,10,423. ’ B. Sanjiva Rao and M. R. A. R,ao, 10th ZnternaIional Congress of Ckernistry, 1938,3,462. 6 M. R. A. Rao, Proc. Indian Acod. Sci., 1940,11,162.
Precipitation of lead sulphate from homogeneous solution by hydrolysis of snlphamic acid (Received 10 June 1964. Accepted 6 December 1964)
THEtechnique and advantages of precipitation from homogeneous solution have been amply presented by Gordon, Salutsky and Willard.’ They also reviewed the methods that have been employed to generate sulphate ions for the determination of barium, calcium, strontium and lead. Elving and Zook’ precipitated lead sulphate by hydrolysis of dimethyl sulphate in 70-80x methanol. Satisfactory accuracy and precision were obtained for amounts of lead in the range of 10 to 100 mg, except in the presence of large amounts of iron(II1) and aluminium(II1). The conditions under which small quantities of lead are precipitated arc somewhat stringent. The concentration of the methanol, amount of dimethyl sulphate added and digestion t‘ime required are dependent upon the quantities of lead and foreign ions present. There is also a tendency for the precipitate to “creep.” Jamagin and Kenneth precipitated lead sulphate by hydrolysis of sulphamic acid catalyzed by the presence of potassium chlorate. A small-sized, uniform precipitate was formed, the volume of which was measured after centrifugation. The successful use of the hydrol sis of sulphamic acid for the precipitation of barium sulphate *s6led to the present investigation oP the precipitation of lead sulphate by a similar procedure. EXPERIMENTAL All reagents met American Chemical Society specifications of purity. Stdek solutions of lead nitrate. Prepared by dissolving the reagent in distilled water. Definite, volumes of these solutions, measured by means of pipettes, were used in subsequent analyses. The quantity of lead present in the solution delivered by a given pipette was determined by evaporating the solution with an excess of sulphuric acid in a platinum dish. The lead sulphate thus obtained was ignited to constant weight in an electric muflle furnace at 550-600”. Stock solutions of possible interfering ions were prepared by dissolving the corresponding salts in distilled water. National Bureau of Standards copper-base alloys were aqalysed to check the analytical procedure. Apparatus Filtering media. Both porcelain filtering crucibles (Coors, fine porosity) and filter paper were used
successfully for the filtration. Some difficulty was encountered in bringing the porous porcelain crucibles to constant weight if the excess sulphuric acid solution was not removed by a final wash with ethyl alcohol. With either medium, the precipitate was ignited to constant weight in-an electric muffle furnace at 550-600”. Preliminary experiments
Preliminary tests were made to determine the optimum conditions necessary to effect complete precipitation of the lead sulphate. For these tests, 25 ml of lead nitrate stock solution containing approximately 100 mg of lead ion were ipetted into 250-ml beakers. A weighed portion of reagent grade sulphamic acid and suIEcient disti Eed water to give a solution volume of 100 ml were added to each sample. These solutions were heated to incipient boiling for varying times up to 2 hr. Portions of the supematant liquid were tested for completeness of precipitation by adding dilute sulphuric acid. Optimum conditions were obtained when 2 g of sulphamic acid were added to the solutions and the period of heating was 1 hr. The use of O-5- and l-g portions of sulphamic acid gave results which were sli htly low. The heating time and temperature were more critical than the amount of sulphamic acl*d.
298
Short communications
In the analysis of many materials containing lead, such as brass and other alloys, the sample is dissolved in nitric acid. After the removal of tin, frequently the solution is evaporated almost to dryness to remove the excess nitric acid, either before or after the addition of sulphuric acid. In the I, sulphamic acid procedure, if nitric acid is present, sulphate ions are produced homogeneously by the following reaction in addition to the hydrolysis reaction: NHISOII- + NOs- -+ SO,*- + N1O + H*O. TABLE I.-DETERMINATION
Cation added, mg
_
None
Taken 10.6
ii%
Av. None
99.7
Av.
WY
Al(II1) 100
99.7 9R
Av. AI
10
Av. Al(W) 10
Av. Cu(II) 100
Av. Cu(I1) 10
99.2
9= 11.7
ii? 99.7
Gi 99.2
Av.
99.2
Cu(II) 10
10.6
Av.
m
Fe(W) 100
99.7
Av.
W7
Fe(II1) 10
99.2
Av.
OF LEAD IN PRESENCE OF FOREIGN CATIONS
Lead, mg Found Error
Cation added, W
Taken 99.7
10.7 10.5 10.7 10.6
+01 -0.1 so.1 0.0
Mn(II) 100
99.8 99.9 99.8 998
$01 $02 +01 Gi
Av.
99.8 99.5 99%
+@l -0.2 -0.1
98.7 99.1 99.9 -_ 99.2
-0.5 -0.1 +07 0.0
11.5 11.9 11.8 li
--02 +02 $0.1 0.0
99.8 99.8 99.7 !%G
$01 +0*1 0.0 +0*1
99.1 99.0 98.9 %G
-O*l -0.2 -0.3 -0.2
10.2 10.3 IG?
-0.4 -0.3 -_.__ -0.4
99.8 99.8 100.4 1BiI
+0*1 +0*1 +0*7 $0.3
99.1 99.3 99.0 99.1
-0.1 so.1 -0.2 -0.1
9m
Mn(II) 10
99.2
Av.
!%G
Mn(lI) 10
106
Av.
iG%
Ni(II) 100
99.7
Av.
99.7
Ni(II) 10
Av. Ni(I1) 10
99.2
9!z 11.7
Av.
11.7
Zn(I1) 100
99.7
Av. Zn(II) 10
Av. Zn(II) 10
W 99.2
9X 10.6
Lead, mg Found Error 99.0 99.4 99.7 99.9 99.7 9%
-0.7 -0.3
99.4 99.4 99.2 _99.3
+0.2 +0.2 0.0 +0*1
10.4 10.3 10.8 iiG
-0.2 -0.3 +0*2 -0.1
99.8 99.5 99.5 99.6
to.1 -0.2 -0.2 -0.1
99.4 99.2 99.3 9!G
$0.2 0.0 so.1 +0*1
11.6 11.6 11.6 -. 11.6
-0.1 -0.1 -0.1 -0.1
99.9 99.9 99.9 99.9
+0.2 $0.2 +0.2 +0*2
99.4 99.4 99.2 99.3
+0*2 $0.2 0.0 +0*1
t-X.: 0.0 -0.2
10.2 -0.4 10.4 -0.2 10.6 0.0 Av. 10.6 104 -0.2 Mean deviation of all results: 0.18 mg
Short communications Thus, in the procedure the nitric acid.
developed,
299
the sulphamic acid was added before the evaporation
to remove
Procedure The following procedure is based on the preliminary investigations. Acidify the solution, containing up to 100 mg of lead ion, with 10 ml of dilute nitric acid, or use the filtrate from the tin determination of a copper-base alloy. Dilute to approximately 50 ml and add 2 g of solid sulphamic acid. Cover the beaker with a raised watch glass and heat on an electric hot plate at incipient boiling until the volume is reduced to 2-5 ml. Add 25 ml of water and digest for 30 min on a hot-plate or steam-bath. Cool to room temperature and filter, using a weighed porcelain filtering crucible or ashless filter paper. Wash the precipitate five times with 1: 20 sulphuric acid, then five times with small portions of 50% ethyl alcohol to remove traces of sulphuric acid. Ignite the precipitate to constant weight in an electric muffle furnace at 550-600”. TABLE II.-DETERMINATION
Standard
OF EAD IN NATIONAL BUREAU COPPER-BASE ALLOYS
OF STANDARDS
Sample No. 37 Sheet Brass
Composition
%”
Lead found, %
Error, %
Lead (as sulphate) Lead (as oxide) Copper Iron Nickel Tin Zinc
0.964 0.989 70.290 0.290 0.520 1.013 26.890
0.952 0941 0.930
-0.012 -0G23 -0.034
0941 0*007
-0.023
Lead found, %
Error, %
Mean Mean deviation
Standard Composition
%’
Lead Antimony Copper
1.52 0.16 88.33
Iron Nickel Tin Zinc
0.12 0.13 790 1.89 Standard
Composition Lead Aluminium Antimony Arsenic Copper Iron Nickel Phosphorus Sulfur Tin Zinc
Sample No. 52 Cast Bronze
150 -1.49
-0.02 -0.03
1.50 0.005
-0.02
. Mean Mean deviation
Sample No. 63 Phosphor
Bronze Bearing Metal
%”
Lead found, %
9.74 0.05 0.55 0.09
9.67 9.71 964 -
-0.07 -0.03 -0.10
0.02 967
-007
78.05 027 z8
Mean deviation
Error, %
z:: 048
a National Bureau of Standards Analyses. Interferences In order to study the effect of foreign cations on the determination of lead b the foregoing method, a series of tests was conducted in which 10 or 100 mg of the cation were a L!ded to the lead nitrate solution before the addition of sulphamic acid. The cations employed in this study were those which are most commonly encountered m the analysis of lead alloys.
Short communications
300
Table I shows the results of these analyses. The pmsence of the foreign cations listed in the table does not appear to have any effect on-the determhration of lead by thd method. Several determinations were made in which the preci itation was accomplished in a 50% ethyl alcohol solvent. Comparable results were obtained, but Pore&n cations at high concentrations were partially precipitated as the sulphates. Analysis of standard samples Results of the analysis of National Bureau of Standards copper-base alloys by the sulphamic acid procedure are given in Table II. A l-g sample of alloy was dissolved in dilute nitric acid. Insoluble oxides were removed by filtration following the evaporation of the solution almost to dryness and redissolving the soluble nitrates. The filtrate was then analysed for lead by the foregoing procedure.
DISCUSSION The determination of lead as the sulphate can be accomplished b generation of the sulphate ion homogeneously in solution by the slow hydrolysis and oxidation orysulphamic acid in an aqueousnitric acid solution. Excellent results were obtained in the anal&s of samoles containine 10-100 ma of lead. Coarse, well-formed crystals of lead sulphate are prod&d which &e readily tran;ferred fro; the reaction beaker to the filter. Troublesome %reeping” of the precipitate does not occur and the lead sulphate is easily washed free from adsorbed ions. Photomicrographs in Figs. l-3 show that there is little, if any, difference in the size of crystals of lead sulphate produced by the ordinary sulphuric acid method and by the homogeneous precipitation methods in alcohol-water solutions using dimethyl sulphate or sulphamic acid. Fig. 4 shows the remarkable increase in sire and regularity of the shape of the crystals of lead sulphate formed by homogeneous precipitation with sulphamic acid in aqueous solution. The crystals produced by the sulphuric acid procedure are more needle-shaped than those formed by homogeneous precipitation. All photographs are at the same magnification. As shown in Table I, the average deviation of all results from the true value was @18mg. This average deviation did not vary signdlcantly with either the amount of lead taken or the amount of foreign cation present. The accuracy and precision of the method for the analysis of three National Bureau of Standards cop r-base alloys are given in Table II. The method is believed to be superior to the other methods p” or the gravimetric determination of lead as the sulphate, in that the conditions for quantitative precipitation are less stringent. Acknowle&ement-The authors wish to express their appreciation to Dr. 0. F. Edwards, Department tals and to the National Science of Microbiology, for the photomicrographs of the lead sulphate Foundation for partial support of the project by a grant fromciKs t e Undergraduate Research Participation Programme. Department of Chemistry University of Kentucky Lexington, Kentucky, U.S.A.
J. E. KOLES P. A. SHINNERS W. F. WAGNER+
Summary-The determination of lead as the sulphate is accomplished by generation of the sulphate ion homogeneously from the slow hydrolysis and oxidation of sulphamic acid in an aqueous-nitric acid solution. Samples containing 10-100 mg of lead from copper-base alloys or solutions containing varying amounts of aluminium(I11). copper(H), iron(II1). manganese(H), nickel0 and zinc@) ions have been analysed successfully. Coarse, well-formed crystals are obtained, which filter easily. Zusanunenfassuag-Die Bleibestimmung als Bleisulfat wurde so durchgefilhrt, daB das Sulfat homogen durch langsame Hydrolyse und Oxydation von Amidosulfont&ure in w&&iger, salpetersaurer Losung erxeugt wurde. Proben mit 10-100 mg Blei aus Legierungen auf Kupfergrundlage oder aus Liisungen mit wechselnden Mengen Al(III), Cu(II), Fe(W), Mn(II), Ni(II) und Zn(II) wurden mit Erfolg analysiert. Grobe, gut ausgebildete Kristalle wurdqn erhalten, die sich leicht flltrieren l&en. l
To whom correspondence concerning this work should be sent.
FIG. 1.-Lead
FIG. 2.-Lead
sulphate precipitated by conventional sulphuric acid method.
sulphate precipitated from homogeneous solution by hydrolysis of dhnethyl sulphate.
300
FIG. 3.-Lead
sulphate precipitated from homogeneous solution by hydrolysis of sulphamic acid in 50 % ethanol.
FIG. 4.-Lead
sulphate precipitated from homoge?eous solution by hydrolysis of sulphamic acid in water.
Short communications
301
R&rum-n a dose le plomb a Petat de sulfate en g&&ant l’ion sulfate en milieu homogene par hydrolyse lente et oxyda@nt de l’acide sulfamique en solution eau-acide nitrique. On aanalysc avec succ&sde.sBchantillons d’alliages base de cuivre contenant 10 a 100 mg de plomb, ou des solutions contenant des quantites variables de Al(III), Cu(II), Fe(‘lII), Mn(II), Ni(I1) et Zn(II). On obtient de gros cristaux bien form&s, aisement filterables. REFERENCES 1 L. Cordon, M. L. Salutsky and H. H. Willard, Precipitation from Homogeneous Solution. John Wilev and Sons, Inc., New York, 1959. * P. J.~Elving and W. C. Zook, Anily$. Chem., 1953,25,502. ’ R. C. Jarnaain and C. T. Kenner. ibid.. 1952.24.2016. 4 W. F. Wag& and J. A. Wuellner, ibid:, 1952,24, 1013. 6 L. Cordon and L. Rowley, ibid., 1957,29,34.