V O L U M E 28, NO. 10, O C T O B E R 1 9 5 6 Bearing these generalizations in mind, it should be possible to identify almost any volatile aromatic amine by its behavior on two or more types of chromatogram. CONCLUSIONS
The advantages of the gas-liquid chromatogram in the analysis of aromatic amines may be summarized as: The method is highly sensitive and quantitative results are easily obtained. Information on the structure of an unknown amine can be obtained by studying its behavior on two or more types of column. Relative retention volumes are put forward as physical constants as useful in identification as melting points, boiling points, etc. LITERATURE CITED (1) J a m e s , A. T., Biochem. J . 5 2 , 2 4 2 (1952). (2) J a m e s , A. T.. M a r t i n , A. J. P., Ibid., 50, 679 (1952). (3) Ihid.. 6 3 , 144 (1956).
1567
Table 111. Constancy of Ortho Effect in Primary Amines Replaced by Group Capable of Acting as Hydrogen Bond Acceptor (Evidenced by ratio of retention volume of p - isomer t o 0 - isomer) Benzyldiphenyl Substituent Group Liquid Paraffin Lubrol MO -F -c1 -Br
-1
...
-0CHs -0CzHh --SHn
1.78 1.54 1.59
... ...
1.26 1.48
(1) J a m e s , -4. T., Martin, -1.J. P., Brit. M e d . Bull. 10, 170 (1954). (5) J a m e s , d.T., M a r t i n , A. J. P.. J . A p p l . Chem. 6 , 105 (1956). (6) James, -4.T., M a r t i n , A. J . P., S m i t h . H. G., B b c h e n . J 5 2 , 238 (1952). (7) Martin, A. J . P., J a m e s , -4. T., Ibid., 6 3 , 138 (1956). RECEIVED for review Iiovember 23, 1955. Accepted June 2, I956
Colorimetric Determination of Fluoride in Water by Meteropoly Blue System ROBERT
P. CURRY1 and M. G. MELLON
Department of Chemistry, Pordoe University, Lafayette, Ind.
A new method for the determination of fluoride in waters utilizes the distillation of fluoride as silicon tetrafluoride from a sulfuric acid medium. The silicon tetrafluoride is carried by a nitrogen gas stream into a sodium borate-boric acid buffer and hydrolyzed, after which the soluble silicate is determined by formation of molybdosilicic acid and subsequent reduction to the corresponding heteropoly blue. This method affords accurate and precise determination of fluoride in the range from 0.1 to 2.0 mg. The effects of the following variables were investigated : the presence of 25 diverse ions, distillation time, and water concentration on the distillation system. Beer's law is followed from 0.1 to 2.0 mg. of fluoride with a standard deviation of 0.024 mg. The sensitivity of the method is 0.18 absorbance unit per 0.1 mg. of fluoride.
and Shuey (14) improved the distillation. The procedure and apparatus described here are modifications of those of Adolph, Shuey, and Wagner and Ross. The heteropoly system involving molybdosilicic acid and its blue reduction product are well knovn, and this heteropoly blue method is recommended for determining silicate in water, The recommended reagent for reducing molybdosilicic acid to the blue product is a solution of sodium hydrogen sulfite, disodium sulfite, and l-amino-2-naphthol-4-sulfonic acid. 1 survey of the literature revealed no attempt to establish a method for fluoride in water based on the formation of molybdosilicic acid from the silicate formed by hydrolysis of silicon tetrafluoride after the removal of the fluoride from the sample by volatilization as silicon tetrafluoride. The following reactions are assumed to be involved:
+ SiOnHzSOc SiF, + 3H20 + SO3 heat SiF4 + HzB03- + 2 OHSi03-- + BF-a + 2 H 2 0 4HF
T
recent ext'erision of fluoridation of water supplies eniphasizes the need for a better method of determining fluoride in 110th treated and untreated waters. This study &-as undertaken to investigate the possibility of making such det,erminationa nsing reactions of heteropoly systems in conjunction with the distillation of fluoride as silicon tetrafluoride from concentrated riilfuric acid. I n st,rongly acidic solution fluoride reacts with sources of silicon t,o form volatile silicon tetrafluoride. When this gas is passed into an aqueous solution, hydrolysis yields silicic and fl(iosi1icic :i.cids. Bein and Wohler (2, 18) xwre among the first t,o establish analytical methods for fluoride based on this volat,ility. -1dolph (1) distilled silicon tetrafluoride from concentrated sulfuric acid and titrated the liberated fluosilicic acid. Penfield (11) collected the distillate in an alcoholic solution of potassium chloride and weighed the insoluble potassium fluosilicate. Wagner and Ross (16) used distillation for separating fluorides quantitatively, HE
1
Present address, Ethyl Corp., Baton Rouge, La.
---+
+
Sios--
+ 12 hIoOa-- + 22 H + + S i ( ? * 1 0 ~ 0 ~ ~+ ) ~HS03-4
+
S ~ ( M O ~ O ~ , , ) ~11- ~H20 -+
heteropoly blue
Feigl and Krumholz (4)and Feigl and Leitmeier (5) used this 3equence of reactions for the qualitative identification of fluoride. Peregud and Boikina (12) describe the determination of fluoride in gas streams of fluororganic compounds by decomposing the compounds a t 900" C. in a oxygen stream in the presence of quartz and platinum and hydrolyzing the silicon tetrafluoride formed. Subsequent formation of molybdosilicic acid and determination of the silicate by visual comparison complete the determination. GENERAL EXPERIMENTAL WORK
Apparatus. Photometric measurements were made in 1-cm. matched cells with a Cary Model 10-llM recording spectrophotometer. All pH measurements were made with a Beckman Model H-2 glass electrode pH meter.
ANALYTICAL CHEMISTRY
1568
The borosilicate glass apparatus used for the distillation and hydrolysis of the silicon tetrafluoride (Figure 1) was an adaptation of that used by Adolph ( I ) , Shuey ( 1 4 ) , and Wagner and Ross (16). The inlet, D, into the distilling flask for the carrier gas, or degassing stream, extended to n-ithin 0.5 cm. of the bottom of the distilling flask. The distilling flask was heated by means of a heating mantle, G, which xvas connected to a Variac for regulating the temperature. Reagents. Solutions used in the color development were made up according to standard methods ( 3 ) . A solution of ammonium molybdate was prepared by dissolving 50 grams of ammonium heptamolybdate [( S H ~ ) B ? V I O ~ O Z ~ . ~ H Z O ] in about 400 ml. of distilled water and diluting- to 500 ml. in a volumetric flask. A solution of 6,V hydrochloric acid was prepared by diluting rearrent arade acid, suecific -aravitv" 1.19. volume for volume with distilled h a t e r , The reducing solution was prepared by dissolving 1.0 gram of l-amino-2-naphthol-4-sulfonic acid and 2.0 grams of disodium sulfite in 100 ml. of distilled water. This solution was added to a solution of GO grams of sodium hydrogen sulfite dissolved in 300 ml. of distilled water. The final solution should be nearly .. colorless and should be discarded if it becomes colored on aging. It should be stored in a brown bottle and kept in the dark when not in use. Figure 1. Distillation apparatus The sodium borate-boric acid buffer used as the receiver solution was prepared by dissolving 10 grams of sodium borate decaA . 250-ml. Erlenmeyer flask E. l25-ml. gas washing bottle B . 3-way distilling flask head F . Vacuum tubing hydrate in 500 ml. of distilled water and adjusting the pH to C. 125-ml. dropping funnel G. Heating mantle 8.5 with 6 N hydrochloric acid. D. Inlet for carrier gas A standard silicon stock solution was prepared by dissolving Connection between A and B is standard 29/42 joint 5.070 grams of sodium metasilicate ( Na2Si03.9H20)in water and diluting to 1 liter with distilled water. This solution was standardized by the recommended gravimetric procedure (S). The gas washing bottle was filled with about 80 ml. of the sodium A 100-ml. portion diluted to 1 liter was used as the stock soluborate-boric acid buffer. Tank nitrogen was used as the carrier tion. It contained 0.050 mg. of silicon per ml. gas, and no pretreatment was found necessary. The nitrogen A standard solution of fluoride was prepared by dissolving rate was controlled by means of a reduction valve and a needle 2.210 grams of reagent grade sodium fluoride in 500 ml. of disvalve. After the distilling assembly containing the fluoride was tilled water and diluting to 1 liter in a volumetric flask. closed, the nitrogen stream was started and the inlet tube of the Because storage in glass leads to silicon contamination, all gas Rashing bottle was put in place. This sequence was used reagents were stored in polyethylene bottles with the exception so that water would not wet the inside surface of the inlet tube of the reducing and hydrochloric acid solutions. of the bottle, which would lead to hydrolysis of the silicon tetrafluoride in this tube and make rinsing necessary to ensure comColor Reaction. Despite the previous thorough examination plete recovery of all of the silicon. The nitrogen rate was adof the heteropoly blue system, a study of the color reaction was justed to about 125 ml. of gas per minute passing through the system. After the sample was inserted, the system closed, and deemed necessary because of the presence of fluoride ions. the nitrogen flow started, 50 to 60 ml. of concentrated sulfuric Large amounts of fluoride ion interfere in the determination of acid (specific gravity 1.84) was added to the distilling flask silicon by this method, presumably because of formation of through the dropping funnel. After the addition of the sulfuric fluosilicate ion. To remove this interference, a borate buffer acid over a period of 2 to 3 minutes, heating was begun. The rate of heating was not a critical factor, the only requirement was used to obtain the fluoborate anion and make all of the silicon being that the sulfuric acid be brought to the temperature where available for molybdosilicic acid formation and subsequent it began to dissociate to water and sulfur trioxide and that the reduction. distillation be carried out for 15 minutes after the dissociation temperature was reached. If the rate of heating used is such The study was carried out by taking various amounts of the that the required temperature is reached in about 30 minutes, standard silicon solution and developing the heteropol blue the distillation can be completed in about 45 minutes. color in the sodium borate-boric acid buffer medium w i d variAfter the distillation was completed, the solution frqm the ous amounts of fluoride present. N o interference due to fluoride gas washing bottle was transferred to a 100-ml. volumetric flask was found when the mole ratio of fluoride to silicon did not exceed and diluted to volume. The solution was then transferred to a 6. Close adherence t o Beer's law was observed for the silicate 250-ml. Griffin beaker and the pH adjusted to between 6 and 8, system in the sodium borate-boric acid buffer medium, with using 10LV sodium hydroxide. The color development procedure no change in sensitivity noted upon addition of 4 moles of fluoride was then carried out. per mole of silicon. The procedure which gave the most accurate and reliable The results obtained from the distillation and color developresults was as follows. To a 100-ml. sample in which the silicon ment procedures showed good adherence to Beer's law. The is to be determined, add 2.0 ml. of ammonium molybdate solusensitivity was 0.18 absorbance unit per 0.1 mg. of fluoride. tion. Allow to stand for 1 minute, then add 1.0 ml. of 1 to 1 hydrochloric acid. The p H of the solution should be 1.5 =k 0.3. Recoveries of silicon equivalent to the fluoride were not quantiAfter 3 minutes, add 2.0 ml. of reducing reagent. Allow the blue tative. From 78 to 80% of the silicon expected, based on the color to develop for 10 minutes, then measure the absorbance distillation of all of the fluoride as silicon tetrafluoride, were oba t 700 mp in 1-em. cells, using distilled water as the reference tained. However, the empirical factor remains constant as far solution. Distillation of Fluoride as Silicon Tetrafluoride. The distilas can be measured by the color system. Variations in design lations were carried out generally following the procedure of of apparatus, changing the p H of the receiver solution, and addiAdolph and others (1, 14, 16). A number of sources of silicon tion of fluoride to borate and nonbuffered receiver solutions did have been suggested, including ground fused quartz, sea sand, not change the value. Determination of the fluoride in the and ground soft glass. It was found that 50 grams of etched soft glass beads gave results comparable to those obtained using distillate by an independent method showed complete recovery the other suggested materials. of fluoride. As the factor for silicon equivalent to fluoride is Various dehydrating agents have been used to keep the water constant and not easily changed, the fact that it is empirical concentration low enough to ensure quantitative evolution of offers no serious practical objection. the fluoride as silicon tetrafluoride. The use of a dehydrating agent proved unnecessary if the final acid concentration in the Construction of Calibration Curve. Using the conditions distilling flask was kept above 90% by.weight of sulfuric acid. which gave the best results, a calibration curve was constructed Distillations were carried out by adding from 0.1 to 2.0 mg. of by adding 0.00, 0.10, 0.50, 1.00, 1.50 and 2.00 mg. of fluoride to fluoride to the distilling flask from the standard stock solution.
0;
I
_
V O L U M E 28, NO, 10, O C T O B E R 1 9 5 6 the distilling flask, carrying out the distillation for 1 hour with a nitrogen gas rate of 125 t o 250 ml. per minute. After the distillation was completed, the distillate was adjusted t o pH 6 .to 8 and diluted to 100 ml. The color was developed as described previously. Data are given in Table I. Procedure for Water. The water sample (1 liter) is adjusted to pH 9 with sodium hydroxide. The sample is then reduced t o a volume of about 50 ml. by boiling in an iron dish and is transferred t o the distillation apparatus. The solution is then brought t o near dryness (less than 5 ml. of water), cooled, and the distillation carried out from concentrated sulfuric acid for 1 how. After the completion of the distillation, the distillate pH is adjusted t o 8.5 with sodium hydroxide. The solution is then diluted to 100 ml. in a volumetric flask and transferred to a 250-ml. Griffin beaker, followed by development of the color. INVESTIGATION O F EMPIRICAL FACTOR
If all of the fluoride in a sample is evolved as silicon tetrafluoride, an equivalence of 1 silicon per 4 fluorines lvould be noted (Si to 4F = 1.00). If only half of the fluoride were evolved as silicon tetrafluoride, an apparent equivalence of 0.5 silicon per 4 fluorines would be observed (Si to 4F = 0.50:'. I n the work described, the apparent equivalence is 0.80 silicon per 4 fluorines (Si to 4F = 0.80). -4number of explanat,ions can be advanced for Si to 4F values of less than 1. Because there is an appreciable amoiint of boron in glass, some of the fluoride may be evolved as boron trifluoride; some of the fluoride may be evolved as hydrofluoric acid; or a part of the silicon may form molybdateunreactive-silicate on hydrolysis. A short discussion of molybdate-unreactive-silicate and reference t o the original literature on the subject Kill be found in ( 3 ) . Any one or combination of the above possibilities would result in low Si t o 4F values. The Si to 4F value could be made to approach 1.0 by evaporating the distillate to dryness in a platinum crucible and carrying out a sodium carbonate fusion. Aft'er fusion the contents of the crucible Tvere dissolved in water, the solution was made acidic to drive off carbon dioxide, the pH adjusted t o 8, dilution made with sodium borate-boric acid buffer, and the color developed. The results indicated that the expected amount of silicon could he ohtained for a given amount of fluoride if the sole distilling species is silico~itetrafluoride. Because the amounts of fluoride and silicon evolved are so small using 2.0 mg. of fluoride, more n-ork was done using larger anioimts. If one uses 20.0 mg. of fluoride and carries out distillation and color development on a suitable aliquot, the observed Si t o 4F value is 0.82 to 0.84. If the distillate is concentrated and the recommended procediire (5) for converting molybdate-unreactive-silicate to the reactive form is carried out, no change in the Si to 4F \ d u e is noted. However, if the sodiuni c:trlionate fusion is carried out folloir-ed by color development, Si t o 4F values of 0.9'7 t o 1.00 are obtained. Attempts t o obtain evidence for appreciable amounts of boron trifluoride and hydrofluoric acid in the distillate stream were unsuccessful. KO appreciable amount of boron could be detected in the distillate if a borate-free receiver solution was used. ..ltt,empts to trap hydrofluoric acid in a sodium fluoride bed yielded no more fluoride or increase in acidity than could be explained by hj.drolysis or adsorption of silicon tetrafluoride in the bed. If one may extrapolate from the composition of a stream of a 20-mg. fluoride distillation t o the composition of a stresm of a 2.0-mg. distillation, good evidence for quantihtive volatilization of all of the fluoride as silicon tetrafluoride is obtained, and
Table 1. Data Obtained for Beer's Law Plot Fluoride .4dded, hlg.
0.00 0.50 1.00 1.50 2.00
Nnmber of Determinations 4 6 6 6
6
Av.
Absorbance 0 0 0 1
04
47 91
37 1 82
Precision in Absorbance U n i t 0 0 0 0 0
02 03 03 03 04
the low Si to 4F value can be attributed to the formation of molybdate-unreactive-silicate in the hydrolysis step. T h e amount of this molybdate-unreactive-silicate formed is approximately one sixth of the silicon equivalent t o fluoride and the molybdateunreactive-silicate formed is not converted to the reactive form by the usual procedure. EFFECT OF VARI4BLES
Water Concentration and Time. The effect of water concentration in the distilling system on recovery and distillation time was investigated. For this study 2 00 mg. of fluoride was taken and distillations n-ere carried out, varying water concentration in the distilling flask. The time of distillation a t different acid concentrations was also varied. The results obtained indicate that, as long as the water concentration in the distilling flask does not originally exceed 10% by weight, the usual recovery is obtained. As the water concentration is increased, the recovery drops off rapidly for a 1-hour distillation. As the water concentration increases to 15 to li%,a prolonged distillation yields the usual recovery of silicon for 2.00 mg. of fluoride. But when the water content increases to 20% or more, even prolonged distillation does not yield the expected recovery of silicon. Determination of the fluoride in the distillate indicates that all of the fluoride is recovered, This was interpreted t o mean that silicon tetrafluoride ceases to be the sole distilling species as the water concentration reaches 20% by weight, and that silicon tetrafluoride and hydrofluoric acid are both distilled. This was t o be expected because, x i t h an increase in water concentration, the conditions of the Willard and SEnter distillation are approached ( 1 7 ) . If the water concentration is kept below lo%, the distillation time varies with the rate of heating and nith the rate of passage of the carrier gas through the system. If the heating rate is adjusted so that the sulfuric acid is brought to its dissociation temperature in about 30 minutes, and with a rate of nitrogen flon- through the system of about 123 ml. per minute, a distillation of 1 hour is sufficient t o ensure complete evolution of the silicon tetrafluoride. Prolonged distillation does not cause any change in the absorbance for a given amount of fluoride. I n most distillations, maximum yield of silicon tetrafluoride was observed in 45 minutes, but in some cases, Ion- resiilts Tyere obtained with a 45-minute distillation. Nitrogen Flow Rate. The rate at which the nitrogen is passed through the distillation system is another variable. The initial rate was adjusted by counting bubbles of nitrogen passing through the receiver solution per minute. -4fter the initial adjustment, the distillation was carried out m d the volume of nitrogen n hen passed through the system in a given time was obtained from a n-et-test meter. The results showed that a rate of 125 to 250 ml. of nitrogen per minute gave the best results. For a given amount of fluoride, the absorbance was constant in this range. Slower rates gave lo^ results, presumably due t o incomplete removal of eilicon tetrafluoride from the sulfuric acid. K i t h rates more rapid than 250 ml. per minute, the results were also lo%-, presumably due to the fact that some silicon tetrafluoride RYIS carried through the receiver solution and out the exit of the gas n-ashing bottle. Diverse Ions. I n studying the effect of diverse ions, a 500fold excess of the diverse ion was added to the distilling flask as a solid material, and the distillation and the color development were carried out. The amount of fluoride used in all cases was 2.00 mg. riny absorbance obtained which n-as more than 2.5% off the calibration curve mas considered to constitute an appreciable interference. When such a situation occurred, the amount of diverse ions n-as decreased until 110 interference was observed The diverse ions studied can be put into four categories: those forming insoluble fluorides or complexing fluoride strongly; those capable of forming volatile silicon compounds; those capable of forming volatile fluorides; and those capable of forming
ANALYTICAL CHEMISTRY
1570 Table 11. Data Obtained from Natural Water with Sufficient Fluoride Added to Make 1 P.P.M. Fluoride, Mg. per Liter 0.00 0.00 1.00 1 .oo 1.00 1.00 1.00 1.00 1.00 1.00 1.00
Obsd. Absorbance 0.046
0.040 0.93 0.92 0.91 0.88 0.93 0.91 0.87 0 93 0 94
Fluoride, P.P.M. 0.005 0.000 1.02 1.01 1.00 0.97 1.02 1.00 0.96 1.02 1.03
Dev.
+o.oz
+O.Ol 0.00 -0.03 +0.02 0.00 -0.04 +0.02
+0.03
heteropoly acids. Ions studied for possible interference were: C1-, Br-, CZHJOZ-, HZB03-, HzPOd-, S b + + + , As+++, As+6, Sn++, Snf4, Mg++, Ca+&, Ba++, F e + + + , 8 1 + + + , Hg++, and Mn++. Of these ions, only borate and acetate offer a serious interference a t a 500-fold excess level. The borate interference can be brought within the permissible limit by decreasing the excess to 20-fold. Its interference is probably due to the volatility of boron trifluoride, which would be formed to an appreciable extent under the conditions of the distillation with such a large excess of borate. The acetate interference was shown to be due to a buffering effect, and can be eliminated by adjusting the distillate to p H 6 before addition of the reagents. The only cationic interferences noted were the result of precipitation of salts of volatile cations under the conditions of color development. They can be eliminated by cancelling out the absorption due to the precipitate. APPLICATION TO NATURAL AND FLUORIDATED WATERS
Despite the study of the effect of diverse ions, it was deemed advisable to apply this method to the determination of fluoride in a water supply in which the fluoride content was k n o w . For this purpose, natural water samples known to contain a negligible amount of fluoride were selected. Two runs were made on samples of this water to establish the fact that the fluoride content was less than 0.10 p.p.m. T o this water was added enough sodium fluoride to obtain 1.0 p.p.m. of fluoride. The procedure was then carried out as given previously for water. Specht (16) gives precautions to be observed when concentrating fluoride solutions. The results obtained are shown in Table 11. The data indicate that this method is applicable to natural waters and show that the materials present in the water sample did not change the sensitivity of the method from that observed when only fluoride was present in the distilled water. The standard deviation calculated from these data is 0.024 mg. of fluoride. The method was also applied to the fluoridated water supply of Lafayette, Ind. This water contains 0.9 p.p.m. of fluoride, the concentration being calculated on the basis of mean pumping rate and weight of sodium fluosilicate added per hour. A 12liter sample of the water was obtained and the fluoride content determined by the heteropoly method and the method of Megregian (9),which is based on the effect of fluoride on a zirconiumEriochrome Cyanine R lake. This spectrophotometric method has the advantage of being relatively free of interference, as it is necessary only to correct for sulfate and destroy free chlorine and other oxidizing agents. If aluminum, iron, and phosphate concentrations are low, no distillation is required. The method is rapid, sensitive, and one of the more accurate colorimetric methods available for the determination of fluoride. One-liter samples were evaporated to 50 ml. in an iron dish, transferred to the distilling flask, and boiled to near drynes,s. Then they were distilled and the color Fas developed and measured. The turbidimetric determination of sulfate and the colorimetric
determination of fluoride were carried out on other samples and the fluoride concentration in the water sample was obtained. The fluoride concentration obtained by running eight samples by the Megregian method was 0.844 Z!= 0.021 p.p.m., with a standard deviation of 0.014 p.p.m. The fluoride concentration obtained by the heteropoly method for six determinations was 0.825 Z!= 0.025 v i t h a standard deviation of 0.022 p.p.m. MERITS OF METHOD
In evaluating this procedure, it should be compared to other available colorimetric methods. I t offers an accurate, sensitive method which is not subject to the normal interferences of a color method. The only major interference is from borate ion, a 20-fold excess of which can be tolerated. Because of the freedom from interference, no previous knowledge of the composition of the sample is necessary except regarding the presence of large amounts of boron. The method is time consuming, about 3 hours being required per determination starting with 1 liter of water sample. The accuracy of the method using a zirconium-alizarin lake, which is the method recommended by the American Public Health Association (S), is within about 0.05 p.p.m. I t is also subject to many interferences. The modified method of Megregian and Maier (IO)using a zirconium-alizarin lake increases the sensitivity to within 0.02 p.p.m., but it is still subject to major interferences from sulfate and chloride. The method developed by Megregian (9), based on the use of a zirconium-Eriochrome Cyanine R lake, cuts the time required for analysis and allows an accuracy within 0.015 p.p.m., but the sulfate concentration must be known and chlorine and other oxidizing agents must be destroyed. The method devised by Ingols ( 7 ) , using the iron-thiocyanate complex, has the advantage of varying range by changing pH of the system. Revinson and Harley’s method ( I S ) , based on decoloration of a thorium-Chrome Azurol lake, has an accuracy of 10% relative in the range from 5 to 90 y. The thorium-thoron method of Horton (6) has an accuracy Tithin 4% in the range from 1 to 50 y, with a standard deviation of 0.85 y. McKenna has published a literature review of methods of determining fluorine and fluoride covering 516 references (8). ACKNOWLEDGMENT
The authors nish to express their thanks to the Eli Lilly Co. for financial support of part of this work. LITERATURE CITED
Adolph, W.H., J . Am. Chem. SOC.,37, 2500 (1915). Bein, S., Z . anal. Chem. 26, 733 (1887). Faber, H. A., ed., others, “Standard Methods for the Examinstion of Water, Sewage, and Industrial Wastes,” p. 185-90, American Public Health Association, New York, 1955. (4) Feigl, F., Krumholz, P., Ber. 62B, 1138-42 (1929). (5) Feigl, F., Leitmeier, H., Tschermak’s minera2og. u. petrog. Mitt.
(1) (2) (3)
40, 1 (1929). (6) Horton, A. D., Thomason, P. F., Miller, F. J., AXAL.CHEM. 2 4 , 5 4 8 (1952). (7) Ingols, R. S., Shaw, E. H., C.,Ibid.,22, 799 (1950).
Eberhardt, W. H., Hildebrand, J.
(8) McKenna, F. E., Nucleonics 8 , No, 6, 24-33; 9, No. 1, 40-9; NO.2, 51-8 (1951). (9) hIegregian, S., AN.4L. CHEM.26, 1161 (1954). (10) Megregian, S., hIaier, F. J., J . Am. Water W o r k s Assoc. 44, 239 (1952).
Penfield, S.L., Am. Chem. J . 1, 27 (1879). Peregud, E. A, Boikina, B. S., Zhur. A n a l . Khim. 8 , 178 (1953). Revinson, D., Harley, J. H., ANAL.CHEW25, 794 (1953). Shuey, G. A., J . Assoc. Ofic. Agr. Chemists 14, 126 (1931). Specht, R.C., ASAL. CHEM.28, 1015 (1956). Wagner, C. R.,Ross, W. H., Ind. Eng. Chem. 9, 1116 (1917). Willard, H. H.. Winter, 0. B., IND.ERG.CHEX., ABAL. ED. 5,7 (1933). (18) Wohler, L., Ann. Phys. [2]4 8 , 8 7 (1839). RECEIVED for review May 3, 195fi. .4ccepted July 6, 195fi.
