V O L U M E 20, NO. 3, M A R C H 1 9 4 8
27 1
relative radioactivity of a carbonate containing solution is calculated as follows:
1.0 _____
A = -v1 w V*X%XC where A is the activity in V I volumes of carbonate solution, V , is the volume of the aliquot of VI used in the preparation of the precipitate, W is the weight of the precipitate in milligrams per square centimeter, and C is the counts per minute corrected for
--
7.8 4.>
.-+
2.6
.-7
resolving time losses and background.
t
z .4
2
.2
n -
5
0
IO
15
20
25
35
30
When a precipitate thinner than 20 mg. per sq. cm. is counted, the activity can be referred directly to a standard prepared with an identical thickness of precipitate, or the method of Reid (6) R hereby a thin sample count is calculated to thick sample activity can be employed. - . LITERATURE CITED
Milliqrams BaCO3 per cm? Figure 2. Relative Activity of Various Thicknesses of Barium Carbonate of Uniform Specific Activity
the “saturation thickness”-i.e., that thickness of sample which absorbs completely all beta rays produced in layers of greater depth-is 20 mg. per sq. cm. Their results are also in’good agreement with the data reported by Reid (6) and with the results of Yankwich, Rollefson, and Norris (6), who present data on the absorption of beta-radiation of radiocarbon by barium carbonate. With precipitates weighing 20 mg. per sq. cm. or more the total
(1) Henriques, F.C.,and Margnett, C., IND.ESG.CHEM.,ANAL.ED., 18, 417 (1946). (2) Henriques, F. C., Kistiakowsky, Margnetti, C., and Schneider, W.G.,I b i d . , 18, 349 (1946). (3) Libby, w.F . v CHEM., 191 (Ig47). (4) Miller, IT. W., Science, 105,123 (1947). ( 5 ) Reid, A. F., in “Preparation and hleasurement of Isotopic Tracers,” p. 83,-4nn Arbor, Mich., J. W.Edwards Co., 1946. (6) Yankwich, P. E., Rollefson, G. K.. and Norris, T. H., J . Chem. Phys., 14, 131 (1946). . RECEIVED ~ p r i24, i 1947. Work carried out under and Mary Markle Foundation.
B
grant from the j o h n
Determination of Silver with Ascorbic Acid E. C. STATHIS, Athens University, Athens, Greece paper (1) Bhowed that gold may be determined ARECENT with accuracy by reduction of gold chloride with ascorbic
acid. This same reagent is effective for the reduction of silver. 2AgNOa
+ CeHSOa +2A4g + C6H606 + 2HN03
Table I. Silver Added Gram 0.1376 0.1063 0.0908 0.0753 0.0695 0.0501 0.0436 0.0351 0.0168 0.0113
Determination of Silver Silver Found Gram
Difference Gram
Table 11. Precipitation of Silver from Solutions Containing Other Ions Silver Added Gram 0.0497 0.0229 0.0450 0,0284 0.0768 0.0887 0.0794 0.0403 0.0772 0.0365 0.0761 0.0395 0.0768 0.0948
Other Metal -4dded Gram Pb++ 0.0325 0.0162 Cu++ 0.0050 0.0031 0.0154 0.0100 Bi++f 0.0300 0.0150 Cd++ 0,0299 0.0149 Ni+f 0.0315 0.0157 Zn++ .O.0103 Cu++ Zn++0.0451Cu 0.0112 Zn
+
Silver Found Gram 0.0496 0.0230 0,0452 0.0284 0,0767 0.0886 0.0794 0.0404 0,0772 0.0364 0.0763 0.0396 0,0770 0.0949
Difference Gram -0.0001 +0.0001 +0.0002 0.0000 -0.0001 -0.0001 0.0000 0.0001
+
0.0000
-0.0001 +o. 0002 +o ,0001 +0.0002 +0.0001
As a result of the investigation of this reaction a new method was developed for the determination of silver, by precipitation with ascorbic acid.
Solutions. Sitric acid, 6 X . Ascorbic acid, 2 grams per 100 ml. of solution. Standard silver solutions, made by dissolving weighed portions of pure silver (Schering pro Analyis) in 6 N nitric acid, removing the acid by evaporation, and diluting the residue to 20 ml. with distilled water. Copper and nickel solutions, made by dissolving weighed portions of pure electrolytic copper and pure nickel wire in 10 ml. of 6 N nitric acid and diluting to 100 ml. with distilled water. Solutions of lead, bismuth, cadmium, and zinc were made by dissolving a suitable pure salt or pure oxide in water or dilute nitric acid and diluting to 100 ml. Their exact strength was determined by the usual analytical methods. Procedure. meigh out 0.1 gram or less of silver into a 100-ml. beaker and add 5 ml. of 6 N nitric acid. Heat gently until solution is complete and then evaporate almost to dryness over a steam bath. Dilute to 20 ml. with distilled water, heat the solution to 90” to 100” C., and s l o d y add 10 ml. of the freshly prepared ascorbic acid reagent. Continue the heating for 15 minutes and promptly filter the precipitate by a porcelain filter crucible. Wash the precipitate with hot water and ignite. Results obtained are given in Table I. Tests upon the effect of added amounts of lead, copper, bismuth, cadmium, nickel, and zinc show (Table 11) that there is no interference. The proposed method has been applied to the analysis of silver-copper alloys. X U. S. silver coin (one dime, 1929) was found t o contain 89.95% silver. The certified figures for this alloy are 90Yc silver and 10% copper. A Greek silver coin (50h. K.II.1901) was found to contain 83.51% silver. The certified figures for this alloy are 83.57, silver and 16.5% copper. LITERATURE CITED (1) Stathis and Gatos, IND. ENCI.CHEM.,ANAL.ED.,18, 801 (1946). RECEIVED May 12, 1947.
