increase the solubility of PAN and its copper complex. RESULTS AND DISCUSSION
Examples of some typical results obtained by this method are given in Table I. The accuracy of this method compares favorably with that of other methods for Pb(I1) analysis, and no problems due to the low solubility of PbHPOa, Pb3(P04)2, or PbdPOJdOH)? are encountered. At pH 5, the titration can be carried out without interference from the alkaline earths and can be performed at a pH as low as 3.5 (3, 4). However, many metal ions will interfere. Some of these
Table I.
Sample Lead(l1) Analyses
Sample PbHPO, Pbd’zOi Pbio(PO4)dOHh PbCL
Theoretical, %
Found, %
68.4 70.4
68.6 69.8 77.2 74.4
are: Cu(II), Ni(II), Hg(II), Fe(III), Cd(II), Zn(II), and Al(II1). This principle of using the dissolution point of an insoluble phosphate as a guide for the amount of EDTA required for titration has also been applied in this laboratory to the titration of calcium in the presence of orthophosphate. This analysis consists of the titration of calcium with EDTA a t
pH 10 using [l-(l-hydroxy-4methyl-2phenylazo) - 2 - naphthol - 4 - sulfonic acid, Calmagite] or murexide as an indicator and Mg(I1) as a back titrant. LITERATURE CITED
(1) Flaschka, H. A., “EDTA Titrations,,’ pp. 90-1, Pergamon Press, ?Jew York, 1959. (2) Flaschka, H., Abdine, H., Chemist A n ~ l y s45,58-61(1956). t (31 Flaschka. H.. Abdine. H.. “The EDTA TiGation,” pp. 25-7, J. T. Baker Chemical Co., Phillipsburg, N. J., 1957. ( 4 ) Reilley, C. N., Schmid, R. W., ANAL. CHEM. 30,947 (1958). 1 - 1
~
FRANKLIN H. BLOOD WILLIAM H. NEBERGALL De artment of Chemistry d a n a University Bloomington, Ind.
The Use of Raney Nickel in the Rapid Determination of Small Concentrations of Nitric Acid in Sulfuric Acid SIR: Many industrial processes require sulfuric acid of known and low nitric acid content. Allen’s modification (1) of Devarda’s method for determination of nitric acid uses Devarda’s alloy, consisting of 45 parts aluminum, 50 parts copper, and 5 parts zinc, to reduce nitric acid to ammonia in alkaline solution, with subsequent Kjeldahl distillation and titration of the ammonia. Devarda’s alloy did not work well for low concentrations of nitric acid and neither did aluminum. Therefore, a Raney nickel alloy catalyst was tried to determine whether rapid and quantitative reaction a t lower levels of nitric acid was possible. EXPERIMENTAL
Reagents. Methyl purple indicator solution, Fleisher’s, available from Fisher Scientific Co. Raney Nickel Alloy, KO. 2813 Raney Catalyst Powder, Raney Catalyst Co., Inc., Chattanooga, Tenn. Procedure. Weigh an appropriate amount of sample to the nearest milligram (Table I) into an 800-ml. Kjeldahl Table I. Sample Weight and Normality of Acid Recommended for Various HNOa Concentrations HNOa in Sample Raney X, sample, weight, Nil HtSO,
%
0.005toO.l 0.1 t o l . O 1.0 to10
1090
grams grams 10 1 f 0.01 10 3 d= 0.01 1 3 f 0.01
ANALYTICAL CHEMISTRY
Titrant 0.005 0.1 0.1
flask. Add 200 ml. of deionized water. Cool the mixture to about room temperature. Add 20 ml. of 50% sodium hydroxide by tilting the flask and pouring in a manner to minimize mixing of the sodium hydroxide and the diluted sample. Without delay add the appropriate amount (Table I) of Raney nickel catalyst and connect the Kjeldahl flask to the Kjeldahl distillation apparatus. Place 25 ml. of saturated boric acid in the Kjeldahl apparatus receiver (a 500-ml. Erlenmeyer flask). While the Kjeldahl flask is connected, swirl the contents to cause mixing. Heat gently and intermittently to maintain a steady and rapid formation of fine bubbles until no further bubbles form (about 30 to 45 minutes). Increase the heat to cause 100 ml. of the solution in the Kjeldahl flask to distill and be collected in such a manner that the condensate passes directly into the boric acid in the Kjeldahl receiver. Remove the receiver, add 3 to 6 drops of methyl purple indicator solution, and titrate with the appropriate sulfuric acid solution (Table I). The color change of the indicator is from green to grey to purple, and the first detectable purple color is the end point. Some analysts may prefer to use a reference solution during titration as a matter of preference. The authors did not use it in the work reported. Determine a reagent blank, following exactly the same procedure as specified above for the analysis of an actual sample. A blank shall be run with every set of samples. Samples containing ammonium salts require separate distillation of a sample for ammonia which is prepared as above
Table 11. Recovery of HNOa in 70% Sulfuric Acid by Reduction with Raney Nickel Alloy Catalyst and Kjeldahl Distillation HNOi “01 HNOs added, found,
% 0.005 0,010
...
0.05
...
mg. 0.58
1.00
...
5.02
...
0.10
10.0
1.0
95
10.0
95
. .
...
...
mg. 0.59 1.05 0.99 4.99 4.84 9.8 10.2 92.4 92.9 90.1 91.8
except that the Raney nickel alloy is omitted. The ammonia found is deducted from the total nitrogen found. RESULTS
Synthetic blends of known composition were prepared and analyzed as shown in Table 11. LITERATURE CITED
(1) Furman, N. H., [‘Skndard Methods of Chemical Analysis, Vol. 1, 6th ed., p. 748, Van Nostrand, New York, 1962.
CHARLES WANBAT D. A. KEYWORTH v. A. BRAND
Universal Oil Products Co. Des Plaines, Ill.
