Aqueous Sodium Borohydride Chemistry Lead, Barium, Mercury, Cadmium, a n d Zinc G. W. SCHAEFFER,' MARY CONCETTA WALLER,2 and 1. F. HOHNSTEDT3 Department of Chemistry, Saint louis University, Saint louis 4, Mo.
b By taking advantage of differences in redox potentials and differences in solubility of reaction products a t various controlled pH values, it is possible to accomplish analytical separations based on the reducing action of aqueous sodium borohydride solutions. Procedures have been developed for the quantitative separation of lead and barium, of cadmium and mercury, and of lead and zinc. A semiquantitative separation of cadmium and zinc can b e achieved.
T
HE first trial experiments of the reducing action of sodium borohydride on inorganic substances in aqueous medium were reported by Hyde, Hoekstra, Schaeffer, and Schlesinger in 1946 ( 2 ) . These studies showed that sodium borohydride qualitatively reduced Ce(1V) t o Ce(II1) and Hg(I1) to Hg(1) and the metal, and that it quantitatively reduced Fe(II1) to Fe(11) in acid solution ( 2 ) . Since that time many of the elements have been investigated a t least in a qualitative way. The reduction can be made the basis for a quantitative determination, as has been illustrated with Pb(I1) (3) and Pt(1V) (6). The standard oxidation potential of this unique reducing agent has been calculated as 1.24 i.olts in alkaline and 0.48 volt in acid solution. However, solutions of the substance exhibit sufficiently high hydrolytic stability to allow their use as a reagent for reduction. The boric acid or borate formed by the oudation of the borohydride does not interfere with the determination of most substancps possibly present in the reduction mixture. If necessary, the boric acid or borate can be separated as the. yolatile trimethouyborane. Any excess boroh?.dride can be readily destroycd by heating or increasing the acidity. Thc procedures emplo5ing sodiuni borohydride are rapid and simplc.. These distinct advantages of-
Deceased.
* Present address, Department of Chem-
istry, Crsuline College, Louisville 6, Ky. Present address, Department of Chemistry, Polytechnic Institute of Brooklyn, Brooklyn 1 , N. Y.
fered by sodium borohydride suggested the utilization of the reagent in the development of analytical schemes for some mixtures of elements that had proved difficult to separate by classical procedures-lead and barium, cadmium and mercury, cadmium and zinc, and lead and zinc. APPARATUS
All precipitates were collected on No. 2001 Selas crucibles. The filtrations were made by connecting the filtering flasks t o a filtering manifold obtained from Aloe and Co. The manifold in turn was connected to a vacuum pump. Ignition of Precipitates. The precipitates were ignited to constant weight in an electric furnace. Reductions. The reductions were carried out in a well ventilated hood. The reduction medium was mixed with a magnetic stirrer, while the sodium borohydride solution was added from a dropping funnel, and subsequently for an hour after the addition of the sodium borohydride solution. I n all cases sufficient NaBH, solution was added to ensure an appreciable concentration of BH4- ion in the final solution after reduction. Filtrations.
REAGENTS
Sodium Borohydride. Approximately 1% aqueous solution was prepared just before use from 98+% sodium borohydride purchased from Metal Hydrides, Inc. Solution concentrations were approximated on a weight basisfor example, 1% NaBH4 was made by dissolving 1 gram of N'aBH4 in 100 ml. of solution. Lead nitrate, 0.0614N and 0.099LV. Barium nitrate. 0.0694N and 0.0814N. Cadmium nitrate, 0.0981N --and 0.0988N. Zinc nitrate, 0.1065X. Zinc sulfate, 0.1504N and 0.0991N. Lead and barium nitrate solutions were standardized by precipitation of P b f 2 and B a f 2 as the sulfates. Cadmium and zinc nitrate solutions and solutions of zinc sulfate were standardized by the pyrophosphate method. hlercury(I1) Nitrate. An approximately 0.1N solution of mercuric nitrate was prepared by dissolving reagent grade Hg(NO&. Nitric acid was added sloTvly until all the salt was dissolved. The mercuric nitrate solution, standard-
ized volumetrically by titrating with a standard potassium thiocyanate solution using ferric alum as the indicator, was 0.0989N. Diammonium Phosphate Solution. The solution was prepared fresh a t the time of use. Reagent grade diammonium phosphate was dissolved in water, phenolphthalein was added, and ammonia solution was added until a pink color just appeared. PROCEDURE
Separation of Lead and Barium. Sodium borohydride is known to reduce lead(I1) quantitatively t o the metal (S), but it has no reducing effect on the barium, as the potential value for the reduction of barium is greater than that of sodium borohydride in either acidic or basic solutions. At high concentrations of hydrogen ion the reduction of lead is incomplete, being subordinate to the water oxidation of the reducing agent. As the acid concentration decreases, reduction of the lead increases until it is complete, under the conditions studied, a t pH 5.0 to 6.0. Calculations based on the Nernst equation and the standard potentials for the couples involved indicated that a t pH 5.63 the potential for the couple BH4- e B(OH)r- is 0.78 volt, assuming an equal activity for both oxidation states, and that this potential would be sufficient to reduce the concentration of the Pb+2 ion in solution to a value of lO-7M. Therefore i t was considered probable that lead could be quantitatively reduced by use of excess NaBH4 a t a p H near 5.6, under which conditions Ba+2 ion should be unaffected. Twenty-five-milliliter aliquots of lead nitrate and 25m1. aliquots of barium nitrate solutions were mixed, and the pH of the solution was adjusted to 5.6 as measured on a Beckman Zeromatic pH meter. Sodium borohydride solution was added and caused an immediate formation of a black precipitate and rapid evolution of hydrogen. After the solution had been mixed for an hour, the reduced lead was collected as a cohesive, metallic gray-black precipitate on a crucible and washed with a special wash solution of pH 6.0. (The wash solution was prepared by dissolving boric acid in boiling water to form a saturated solution. The VOL. 33, NO. 12, NOVEMBER 1961
1719
saturated boric acid solution was cooled, decanted, and treated with sodium borohydride until a p H of 6 was reached.) Samples of the filtrate failed to show any unreacted lead by the lead sulfide test. Various procedures were employed for drying the lead, with the objective of developing a procedure in which the element could be weighed as the free metal. Although the metal appears to be the sole reduction product, assays by direct weighing of the precipitates yield high results. In the case of lead, visual color changes occur after the initial precipitation, ranging from a white to yellow coating on all or part of the gray-black metal surface. Xray diffraction data of the lead precipitates indicate that the samples contain only a mixture of lead and lead oxide ( 3 ) . It is believed that the precipitates are the pure metal which undergoes surface oxidation during the drying process. It does not seem likely that a convenient desk-top procedure based on NaBH, reduction could be developed for the determination of lead by direct weighing of the precipitated metal. Therefore the reduced lead was dissolved in the least possible amount of hot 6N nitric acid. The analysis for lead was made according to the methods and special procedures outlined by Hillebrand and Lundell (1) and by Lundell and Hoffman (4). The average percentage lead recovered was 99.93 i.0.15% (95% confidence limits). The barium solution was acidified, and the barium was determined as the sulfate. The calculated barium recovered after the reduction and separation of the lead was 100.00 0.15y0 (95% confidence limits) of that originally present. The percentages given above are the average results of 14 determinations. The lead content of the stock solutions used ranged from 6.365 mg. per ml. (0.0615 meq. per ml.) to 10.36 mg. per ml. (0.1 meq. per ml.). The barium content of the stock solutions ranged from 4.76 mg. per ml. (0.0694 meq. per ml.) t o 5.60 mg. per ml. (0.0814 meq. per ml.). Separation of Cadmium and Mercury. Cadmium and mercury in oxidation state I1 are usually listed in Group I1 in analytical procedures as elements forming sulfides n-hidh are insoluble in acid solutions. To determine the pH a t which cadmium and mercury individually could be quantitatively precipitated in an analyzable form, a systematic study was made of the percentage recovery of known amounts of the element after reduction of the $2 ions by sodium borohydride a t different initial p H values. Acid solutions of Cd+2 or Hg+* ions or basic solutions containing 1720
ANALYTICAL CHEMISTRY
Table I.
Effect of pH on Reduction of Cd(ll) and Hg(ll) (Based on 4 determinations each)
Initial
Average Recovery,
(9570 Confidence Limits)
PH
Cd
2 5 7 9
100.2 d= 0 . 5 99.54 =t0.9 99.39 f 1.1
11
No visually detectable reduction No visually detectable reduction
Hg 98.89 99.90 99.95 99.76
=I= 0.13
f 0.15
f 0.10 f 0.29
99.63 & 0.53
the precipitated Cd(I1) or Hg(I1) species were stirred during the dropwise addition of the sodium borohydride solution and subsequently for an hour. The resulting solids after reduction were collected on crucibles and washed nith distilled water. The precipitated cadmium was analyzed by direct weighing in the same way as the precipitated lead had been studied and again unacceptably high results were obtained. Again there was evidence of surface oxidation during the drying process. The finely divided black precipitate became covered with a white coating which formed when the precipitate came in contact with air. There was nothing to indicate that Cd+* present in insoluble species in contact with solutions of pH above 7 undergoes any change when a SaBH4 solution is added to the mixture. However, a t a pH of 7 or lower, a finely divided black precipitate is obtained on addition of N a B K solution to the Cd+2 solutions. This precipitate can be pressed easily into a film with a metallic foil appearance. The finely divided precipitate dissolves readily in BH4- free acid with the evolution of gas (presumed to be H2); after the digestion to larger particle size the precipitate dissolves only slowly. These observations on dried samples of the precipitate lead us to conclude that it is Cd metal, which is partially oxidized during the drying process and, perhaps, also during the washing process. The precipitated mercury appears to be pure, and preliminary studies indicate that the weight of precipitate collected corresponds within a few parts per thousand to the weight of mercury in the test samples. In determinations of the percentages of elements recovered, the precipitates were dissolved and standard methods of analysis were employed. In the case of cadmium, the collected solid was dissolved with dilute sulfuric acid. In some cases several drops of nitric acid were necessary to effect complete solution. The cadmium was analyzed gravimetrically by the pyrophos-
phate method. In the study of mercury the reduced metal precipitate was dissolved in hot 6N nitric acid. The Hg(I1) solution was treated with LVnO, and FeSO, solutions to ensure the absence of Hg(1). The mercury was determined volumetrically by titration with a standard thiocyanate solution using ferric alum as the indicator. The results of these studies are given in Table I. A consideration of the values in Table I shows that the maximum recovery and greatest precision were obtained for mercury a t pH 7-the pH value for which the poorest results n-ith cadmium were obtained where there was any reduction of the cadmium. For the analytical separation of cadmium and mercury 25-ml. aliquots of cadmium nitrate (0.0946N) and of mercuric nitrate (0.0989N) were mixed, and the pH of the solution was adjusted to 7. At this pH there was a bright orange precipitate present. Fifty milliliters of 1% SaBH4 solution were added dropwise, and the mixture was stirred for an hour. -4 black precipitate was formed. iit the conclusion of the reaction the pH w-as between 10.5 and 11.0. It was adjusted t o 6.0 with dilute nitric acid. The cadmium species which had precipitated went back into solution, and there was left a gray precipitate of metallic mercury. This mercury was collected on crucibles and rrashed with a solution consisting of a saturated boric acid solution which had been adjusted t o pH 6.0 by the addition of KaB&. After washing, the Hg was dissolved in hot 6N nitric acid and was determined by titration with standard thiocyanate solution. The average percentage of mercury recovered from nine determinations was 99.92 i 0.03% (95% confidence limits). The filtrate was analyzed for cadmium by the pyrophosphate method. The average percentage cadmium recovered was 99.81 =t0.307, (957, confidence limits). The Cd-Hg separations were all approximately equimolar.
Separation of Cadmium and Zinc. Cadmium is often found in association with zinc, which it resembles. The complete separation of cadmium from zinc is difficult, particularly if the zinc is present in large excess. Standard methods call for reprecipitations with hydrogen sulfide and report values that are slightly highby approximately 3%. The method of separation of cadmium and zinc considered in this study is based upon the redox potentials of the ions in their reactions with sodium borohydride and the solubility of zinc hydroxide Ih sufficiently basic solutions. Preliminary experiments with aliquots of the zinc solution, similar to those for cadmium and mercury, indicated no reduction a t any of the pH values studied. Sodium borohydride
added to a mixture of the cadmium and zinc solutions with initial pH values of 2, 5, and 7 reduced the cadmium, increased the pH, and precipitated the zinc as the ‘lydroxide or the borate. The pH of the solution after reduction could not be brought below 6 in an effort to dissolve the white zinc compounds without dissolving the finely divided cadmium precipitate. Therefore, the possibility of reducing the cadmium a t initial pH 2 and dissolving the precipitated zinc compounds before filtration by the formation of the [Zn(NH3)4]+zion was studied. However, on the addition of ammonia solution both the cadmium precipitate and the zinc compound(s) dissolved, despite the presence of excess BH4- ion. The next approach was the addition of KaOH solution to the reduction mixture to form the zinc anionic species. When an excess of sodium hydroxide was added to the reduction products, part of the precipitate dissolved, and the black precipitate was changed to a very fine gray-white precipitate. The mixture was warmed on the hot plate for a half hour to facilitate filtering. The gray-white precipitate then was collected hy filtration and dissolved in dilute sulfuric acid, aiid the solution analyzed for cadmium to give for four determinations a value of 107.5 0.3% (95yo confidence limits) on the basis of tlic original Cd present. A sample of the Cd precipitate Iyas dissolved in 2 S H2S04and gave a positive zinc test with potassium hexacyanoferrate(I1) and diphenylamine. This suggested that careful reprecipitations are necessary t o free the cadmium from the zinc. A sample solution of 25 ml. of Cd(S03)z solution (0.0988N) and 25 ml. of ZnSOl solution (0.15045) was prepared. This test solution contained Zn(I1) ion in excess of Cd(I1). It was water clear when the p H of the solution was adjusted to 2. Fifty milliliters of lY0 NaBH4 solution were added, and a thick black precipitate formed. After the reduction mixture had been stirred for an hour, 40 nil. of 3N S a O H were added with stirring. The resulting mixture was digested on a hot plate for 30 minutes and filtered. The precipitate was washed with hot water and dissolved in 20 ml. of 2N sulfuric acid. The pH of the resulting solution was adjusted to 2 , and a second reduction of the Cd(I1) was effected with sodium borohydride. The reduced cadmium was digested in the presence of 3N NaOH, collected on crucibles, washed with hot water, dissolved in 2N HzS04 and determined by the pyrophosphate method. The cadmium recovered after a second reduction with sodium borohydride analyzed for four determinations 99.96 i. 0.5% (95% confidence limits). The filtrates containing the Zn+2ions were combined and treated with 10 ml. of methanol and 8 ml. of concentrated sulfuric acid. The resulting solution was boiled to expel the boron present as
trimethoxyborane and then evaporated to about 150 ml. The solution was analyzed for zinc according to the pyrophosphate method. The average percentage zinc recovered in four determinations was 97.80 + 0.6% (95% confidence limits). Considering the cadmium alone, good results are indicated, but if one considers the zinc recovery, one questions whether the calculated 99.96% Cd recovered represents only cadmium or whether there are small amounts of zinc present. Polarographic studies of the Zn2P201 and CdzPz07 precipitates dissolved in 2N HCI helped solve this problem. The polarograms for ZnzPzO, proved this product to be uncontaminated by cadmium. However, the polarograms for the CdzPz07showed a small percentage of zinc present. Another reduction may have completely freed the cadmium of the zinc. The fact that the percentages of the cadmium and zinc do not add up to 200% is due to the volatility of the cadmium during the solution process, when the precipitated cadmium metal was heated in an acid medium to hasten the oxidation of the Cd(0) to Cd(I1). When the ratio of the Cd(I1) to Zn(I1) ions present was approximately 1 meq. of Cd(I1) to 1.5 meq. of Zn(II), the final value for the recovery of the Zn(I1) present for four determinations was 97.80 =t 0.6% (95% confidence limits). When the Cd(I1)-Zn(I1) ratio was approximately 1 meq. of Cd(I1) to 7.5 meq. of Zn(II), the average results in four determinations gave a value of 98.07 f 0.11% Zn (9570 confidence limits). Separation of Lead and Zinc. The reaction of sodium borohydride with a mixture of Pb(I1) ions is somewhat similar to the reaction taking place when the sodium borohydride is added to a mixture of Pb(I1) and Ba(I1) ions. The redox potential of the sodium borohydride is high enough to reduce the lead but too low to reduce the zinc. The procedure is complicated by the precipitation of zinc hydroxide or zinc borate in the presence of excess sodium borohydride, and also by the passage of minute particles of reduced lead through the filtering crucibles. This passage of the lead particles through the crucible can be eliminated or greatly retarded by washing the lead precipitate with 6N ammonia solution. A 25-m1. sample of lead nitrate (0.0995N) and a 25-ml. sample of zinc nitrate (0.1065iV) were mixed. The p H of the solution was adjusted to 5.6. Sodium borohydride (50 ml. of 1% aqueous solution) was added, and the reduction medium was stirred for an hour. Fifteen milliliters of concentrated ammonia solution were added, and the
solution was stirred to form the [Zn(KH3)4]+2ion. The reduced lead was filtered from the zinc solution. I t was washed with 6N K ” 3 solution and dissolved in the least amount possible of hot 6N nitric acid. The filtrate was evaporated to one half its volume. The pH of the filtrate was again adjusted to 5.6, and 50 ml. of NaBH4 were added. An immediate darkening of the reduction medium indicated that the first reduction of the Pb(I1) ion had been incomplete. Fifteen milliliters of KH3 solution were added to form the soluble zinc species. The small amount of lead m-as collected on crucibles, washed with 6147 ammonia solution, dissolved in 6N HSO,, and combined with the product of the first reduction. The percentage lead recovered was determined by the sulfate method to be 99.82 0.09% (9570 confidence limits).
*
The percentages given above are the results of seven determinations. The concentrations tried in the Pb-Zn separations were approximately equimolar. The lead content of the stock solutions used was the same-namely, 10.3 mg. of P b f 2 per ml. (0,0995 meq. per ml.). The zinc content of the stock solutions was 3.48 mg. of Zn+2 per ml. (0.1065 meq. per ml.). The zinc solution was treated with 10 ml. of methanol and 10 ml. of concentrated sulfuric acid. It was boiled to expel the boron present as trimethoxyborane. The percentage zinc recovered as determined by the pyrophosphate method x a s 99.92 + 0.22% (95% confidence limits). RESULTS
By making use of the reducing properties of sodium borohydride and the effect of pH upon the solubilities of the products formed, it is possible to separate lead quantitatively from barium, cadmium from mercury, and lead from zinc, and to separate cadmium semiquantitatively from zinc when these metals are mixed as the f 2 ions in the concentrations used in this work. Lead and barium are separated by adding the sodium borohydride solution with constant stirring to the mixture of the +2 ions at pH 5.6, and after reduction separating the lead from the barium by filtration. Satisfactory determinations for the separated barium and lead can be accomplished on each by conversion to the sulfate. The separation of cadmium from mercury is effected by adding the sodium borohydride solution with constant stirring to the mixture of the + 2 ions a t p H 7, and after reduction adjusting the p H to 6, thereby dissolving precipitated species of cadmium. (The cadmium precipitate is insoluble a t pH larger than 6 and is presumed to be finely divided cadmium metal.) The mercury may be filtered from the cadVOL. 33, NO. 12, NOVEMBER 1961
* 1721
mium solution and determined by solution in HNOs and titration with a standard thiocyanate solution. Cadmium can be determined by precipitation as CdNH4POd and conversion to CdZP20.I. Cadmium is separated from zinc by adding the sodium borohydride with constant stirring to the mixture of the +2 ions a t the initial p H 2, and adding 3N NaOH, after reduction, to dissolve the zinc compound(s). After warming on the hot plate for a half hour to increase the particle size of the cadmium precipitate, the hot mixture is filtered. The cadmium precipitate is presumed to be metallic cadmium. For analysis the separated elements may be converted to the pyrophosphates. Results obtained using one reprecipitation are as good as or better than those obtained by the hydrogen sulfide method after a third or fourth precipitation. However, the results obtained as described in the experimental part are not as satisfactory in this case as for the other mixtures studied. The separation of lead and zinc is effected by adding the sodium borohydride with constant stirring to the mixture of the f 2 ions a t initial p H 5.0 to 6.0, and adding ammonia solu-
tion after reduction to dissolve the zinc compound(s). The lead is filtered from the Einc solution, and the filtrate is adjusted to p H 5.6. A second NaBHd reduction is carried out on the filtrate and the resulting lead precipitate isolated as in the first reduction step. The lead from the two reductions may be dissolved in nitric acid, and determined by precipitation as the sulfate. Zinc can be determined by precipitation as ZnNH4P04and conversion to Zn2Pe0,. Excellent results are obtained by this procedure involving a second reduction of lead. To determine whether these methods are adaptable to mixtures with concentration ranges and relative concentrations different from those used in these studies, further experimental work is required. ACKNOWLEDGMENT
The authors thank the National Science Foundation] which helped support the work described. The application of aqueous sodium borohydride for the development of a general inorganic analytical scheme was conceived by G. W. Schaeffer, and the
National Science Foundation Grant was made to support this work on the basis of the proposal prepared by Schaeffer. Work reported in this paper was continued under this grant following the death of Schaeffer, along the general lines suggested by him. LITERATURE CITED
(1) Hillebrand, W.F., Lundell, G. E. F., “Applied Inorganic Analysis,” p. 182,
Wiley, New York, 1953. (2) Hyde, E. K., Hoekstra, H. R., Schaeffer, G. W., Schlesinger, H. I., “Some Properties of Aqueous Sodium and Lithium Borohydride]” Division
of Physical and Inorganic Chemistry,
110th Meeting, ACS, Chicago, Ill., September 1946. (3) Kramer, M., Ph.D. dissertation, Saint Louis University, 1954. (4) Lundell, G. E. F., Hoffman, J. I., “Outlines of Methods of Chemical Analysis,” p. 105. Wiley, New York, 1938. (5) Schaeffer, G. W.]Miniatas, B. O., “Reactions of Aqueous Sodium Borohydride. Reduction of Platinum(1V) and Palladium(II),” Division of Inor anic Chemistry, 138th Meeting, AES, N ew York, September 1960. RECEIVEDfor review May 24, 1961. Accepted August 8, 1961. Presented in part before Division of Inorganic Chemistry, 138th Meeting, ACS, New York, September 1960.
Flame Spectrophotometric Study of Barium JOHN A. DEAN and J. C. BURGER’ Department o f Chemistry, University of Tennessee, Knoxville, Tenn,
T. C. RAINS and
H. E. ZITTEL
Analytical Chemistry Division, Oak Ridge National laboratory, Oak Ridge, Tenn.
Flame emission characteristics of the barium ionic doublet at 455.4 and 493.4 mp, the atomic resonance line at 553.6 mp, and the BaOH and BaO bands at 488 and 513 mp were studied. A prism flame spectrophotometer (Beckman DU), superior in work with bands, and a grating type (Jarrell-Ash Ebert), superior in work with lines, were used. Barium concentrations ranged from 1 to 10 pg. per ml. (Jarrell-Ash Ebert) and 10 to 100 pg. per ml. (Beckman). Effects of flows of oxygen and fuel (hydrogen and acetylene), ratio of these flows, different regions of flame mantle viewed, organic solvents, and various cations and anions were determined. With anionic interferences, the oxygenacetylene has advantages over the oxygen-hydrogen flame; otherwise not. Spectral, condensed-phase, and radiation type interferences were investigated. Several elements interfere seriously. Flame spectrophotome-
1722
ANALYTICAL CHEMISTRY
try is rapid and is more sensitive and accurate than other methods for barium in the concentrations studied.
T
HE flame spectrophotometry of barium has been studied to a limited extent only (4, perhaps because the flame emission intensity of barium is less than that of magnesium, calcium, or strontium. However, of the methods available for the determination of barium in concentrations greater than 2 pg. per ml., flame spectrophotometry has a number of advantages. Watanabe and Kendall (16) have presented a complete flame spectrum of barium. The spectrum consists of an ionic doublet a t 455.4 and 493.4 mp, an atomic resonance line a t 553.6 mp, and a series of BaOH and BaO band structures within the regions from 450 to 610 mp and from 730 to 1000 mp. The 553.6mp line and the 488-mp band are used
most frequently for the flame spectrophotometric determination of barium. Although use of the 553.6-mp line provides the greatest sensitivity, several elements, especially calcium, interfere because they also radiate a t this wave length. The 5 1 3 - u band was used by Shaw (14) in the indirect flame spectrophotometric determination of sulfate. However, if any organic material (solvent) is present, this band cannot be used because there is a strong Co band a t 516 mp, Hinsvark, R i t t wer, and Sell (9) used the 873-mp band to determine milligram quantities of barium in the presence of calcium and strontium. The 873-mp band is not very intense, and a correction must be made for the radiation interference of CaO a t 873-mp. The influence of hydrocarbon solvents on the emission in1 Present address, Electronic Tube Division, Westinghouse Electric Corp., Elmira, N. Y.
