Detection and Estimation of Small Amounts of Fluorine Application of the Zirconium Purpurin Test I. M. Kolthoff
and
Maurice E. Stansby, School of Chemistry, University of Minnesota, Minneapolis, Minn.
The qualitative test for fluorine described uses increasing interest in trihydroxyanthraquinone), 30 cc. of ethanol, and 720 cc. of occurrence of traces a modification of the de Boer-Basart reagent and of fluorine in natural concentrated hydrochloric is sensitive to 0.003 mg. of fluoride. Various acid. products demands a simple, anions have an interfering effect. A simple disspecific, and sensitive test for the The zirconium salt is dissolved tillation method is described by which 0.005 mg. detection and estimation of this in 100 cc. of concentrated hyelement. Of the various methof fluorine can be detected in the presence of any drochloric acid, 100 cc. of water ods mentioned in the literature, cation or anion. being added to insure a clear the method of de Boer and Basart solution. The purpurin is disA procedure for the titration of 0.5 to 15 mg. solved in the alcohol and the re(4,5) seemed the most promissulting solution added slowly of fluorine, using zirconium oxychloride as reing. The method has been with continuous shaking to the modified and extended by agent and purpurin as indicator, is given which zirconium solution. The remainPavelka (9), Alimarin (2), Koone der of the hydrochloric acid is is accurate to 2 per cent. A colorimetric method then added and the solution made (8), Willard and Winter (14), and for quantities of fluorine between 0.01 and 0.05 It up to 1 liter with water. Armstrong (3). However, most is essential that the purpurin be mg. is also described which is accurate to 0.002 of their methods are applied to to the added zirconium solution mg. of fluorine. In the presence of interfering neutral or feebly acid solutions, and not vice versa, since otherwise the solution becomes cloudy. substances the fluorine is separated by a distillathereby losing the inherent adThe mixture is allowed to stand of the de Boer-Basart vantage tion method. overnight and is then ready for method which is applied in a use. The reagent is stable for acid solution. at least 1 month. After 2 or 3 strong hydrochloric In solutions of high acidity considerably fewer substances months the color begins to fade and a precipitate forms. In the absence of interfering substances, the solid, or residue obinterfere, and often a long separation of the fluorine from these tained after evaporating the solvent, is dissolved in 2 cc. of 6 IV" interfering substances can be eliminated. The present method hydrochloric acid and 2 cc. of the reagent are added. The pink uses an 8 N hydrochloric acid solution. color of the reagent will turn yellow immediately if 0.003 mg. or In attempting to determine the fluorine content of stand- more of fluoride is present. To confirm the presence of fluorine, ard ammonium and sodium fluoride solutions by the calcium solid zirconium oxychloride is added a little at a time with The color should turn pink again. If it does not, or if fluoride method, highly variable results were obtained. shaking. a cloudy or orange solution results after the addition of the purBetter results were obtained as follows: purin-zirconium reagent, the presence of interfering elements The final acidity To 25 cc. of ammonium fluoride containing 1 to 2 per cent of which have destroyed the dye is indicated. of the mixture should be between 7 N and 10 N with respect to fluorine and a few drops of ammonium hydroxide strontium chloIf the acidity is greater than 10 N, the color ride solution was slowly added with constant stirring. The fil- hydrochloric acid. of fluorine is orange or yellow; if less than 6 N, the in absence tered strontium fluoride was washed with saturated strontium a cloudy solution forms. The test becomes impossible at acidifluoride solution, dried, ignited, and weighed. In this way a solution was found to contain 1.253, 1.253, 1.254, and 1.255 per ties of less than 4 N. cent of fluorine. Sometimes a precipitate formed which could De Boer and Basart (4, 5) mention sulfuric and oxalic acids not be filtered. However, when filtration was possible, consistent results were obtained and the procedure is superior to the as interfering, and Stone (12) describes the interference of calcium method. phosphoric acid. Phosphates cause the solution to become Three different samples of zirconium oxychloride cloudy in a short time by precipitating the insoluble zirconium phosphate. Borates have no (Zr0Cl2-8H20) were used, one obtained from de influence alone, but prevent the formation of the Boer, one purchased from the City Chemical Comyellow color in the presence of fluoride, unless the pany, and one from the Welsbach Company. The fluoride is present in excess. Nitrates do not inlatter was very impure, even after an ether extracterfere immediately, but upon long standing the tion to remove the ferric chloride. The zirconium content of the City Chemical Company product dye is destroyed. Strongly oxidizing substances was found to be 28.2 per cent (phosphate method) (chlorates, bromates, iodates, etc.) evolve chlorine and 28.3 per cent (precipitation as hydrous oxide and destroy the dye, but can be rendered harmless and weighing as Zr02), respectively (calculated,' with sulfurous acid. Complex fluorides as fluosilicates and borofluorides behave like fluorides. It 28.25 per cent). This product was mainly used in the following work. is evident that the direct color test is fairly limited. The purpurin used was a Kahlbaum product, Generally, a separation according to distillation or precipitation is recommended. recrystallized from alcohol. Distillation Method. The fluoride is disQualitative Test tilled off as silicon tetrafluoride, which is The following substances are necessary to collected in the pink purpurin-zirconium reagent. make one liter of the reagent: 0.16 gram of The distillation apparatus consists of a widezirconium oxychloride, 9 mg. of purpurin (l,2,4r mouth Pyrex flask of about 150 cc. capacity. It is Figure 1
the
THE
.
118
INDUSTRIAL
March 15,1934
ENGINEERING
AND
fitted with a ground-glass stopper (Figure 1) containing an inlet tube extending to the bottom and a second tube ending below the neck of the flask, the other end of which is bent down and sealed in a small test tube. The dry sample is introduced into the flask with about 1 gram of quartz or silica powder and 25 cc. of concentrated sulfuric acid. One cubic centimeter of the purpurin-zirconium reagent is put into the small test tube. A stream of air, dried through concentrated sulfuric acid, is passed through the flask and the latter heated to 140° C. in an oil bath. It is essential that the entire apparatus be perfectly dry before the test is begun. The temperature should never exceed 160° C. A blank test run for 1 hour without any fluoride gave no change in color of the reagent in the small test tube. Longer heating resulted in a gradual change of color of the reagent to orange. The speed with which the reagent changes color depends on the amount of fluoride present as shown in Table I.
Table I. Fluorine Mg, 1.0 0.1 0.05 0.03 0.03
Detection Time
Min. 0.33 1
3
3 5
of
Fluoride
by
Color of Reagent
Fluorine
Y ellow Yellow Yellow
Mg. 0.01 0.01 0.005 0.005
Orange
Yellow
Distillation Time Min. 15
20 30 40
Method Color
of
Reagent
Orange
Yellow Orange-yellow Yellow
The test is sensitive to 0.005 mg. of fluorine with a time of heating of 40 minutes. With 0.0025 mg. of fluorine and 50 minutes of heating the reagent had become orange-yellow. Phosphates, bromides, chlorides, sulfates, sulfites, acetates, oxalates, sulfides, and cations do not interfere. Boric acid in the absence of fluoride turns the reagent an orange color which is easily distinguished from the yellow color obtained with fluorides. It is easy to detect as little as 0.01 mg. of fluorine in the presence of 500 mg. of boric acid. Nitrates and nitrites interfere and destroy the purpurin in the reagent, which turns cloudy yellow. Interference by nitrates and nitrites can be eliminated by dissolving some salicylic acid in the sulfuric acid used, thus transforming the acids into nitro and nitroso compounds. It is recommended to add the sulfuric and salicylic acid mixture at a low temperature (flask in ice) in order to prevent volatilization of silicon fluoride. In the presence of 500 mg. of nitrate or nitrite 0.05 mg. of fluoride could be detected. Chlorates, bromates, dichromates, and some other strongly oxidizing agents interfere. This interference can be eliminated by adding a little sodium bisulfite to the reagent in the small test tube. Iodide in quantities larger than 10 mg. interferes. It can be removed by adding to the aqueous solution of the sample enough silver sulfate to insure quantitative precipitation of the iodide (test filtrate with a little nitrite and acid and carbon tetrachloride). Although tartrates do not interfere in'the direct test for fluoride, they exert an interfering effect in the distillation method. Probably one of the decomposition products formed on heating with sulfuric acid forms a stable complex with the zirconium, causing the color change of the reagent from pink to yellow. Tartrate can be made harmless by addition of enough ferric sulfate to the sulfuric acid. The addition of 5 grams of ferric sulfate overcomes the interference caused by one gram of tartaric acid. In this way 0.01 mg. fluorine could be detected in the presence of 500 mg. of tartrate. When iodides are present, enough silver sulfate is added to the aqueous solution of the sample to decrease the iodide content to less than 10 mg. The filtrate is made slightly alkaline and evaporated to dryness. The dry residue (or the dry sample in the absence of more than 10 mg. of iodide) is mixed intimately with several grams of quartz powder. The mixture is transferred to the distillation flask, and 5 grams of ferric sulfate are added if tartrates might be present. The flask is immersed in ice water and 50 cc. of sulfuric acid containing a few grams of salicylic acid
CHEMISTRY
119
slowly added with vigorous shaking. (In case nitrates and nitrites are absent, the procedure described for fluoride alone should be followed, since the sensitivity in the latter case is greater). The stopper is now inserted in the flask with 1 cc. of the reagent, saturated with sulfur dioxide, present in the small attached test tube. The rest of the procedure is the same as deare
scribed above.
Sensitivity, 0.005 mg. of fluorine after 40 minutes; 0.05 mg. in the presence of nitrates and nitrites.
Precipitation Method. The distillation method is the most sensitive and reliable test for the detection of fluoride in the presence of interfering anions. However, for ordinary class work it may be advantageous to have a less sensitive method not requiring special apparatus. The solution of the unknown is acidified with hydrochloric acid in a platinum dish and heated with an excess of barium chloride. The precipitate is filtered off and washed a few times with dilute hydrochloric acid. A few cubic centimeters of 4 N -acetic acid, a drop of methyl orange, and sodium hydroxide are added until the color of the solution corresponds to a pH of 4.5. An excess of calcium chloride is then added, followed by some ammonium oxalate. At this point the volume should not exceed 25 cc. The precipitate is filtered and washed twice with an acetate buffer of pH 3.5. The precipitate is dissolved in a few drops of concentrated hydrochloric acid, a little permanganate added to remove the oxalic acid, and the permanganate removed with an excess of sodium bisulfite. The resulting solution is tested as described in the beginning of the paper. The method is sensitive to 0.1 mg. of fluorine in the presence of interfering anions. Stone’s method {12) is simpler in the presence of phosphates, sulfates, and oxalates, but is less reliable than the methods described above in the presence of interfering substances. The authors had considerable difficulty in detecting 0.03 mg. of fluorine in the presence of phosphate or sulfate by Stone’s method, since there was always a certain amount of doubt as to whether the change of color was due to the fluoride on the one hand or to the phosphate or sulfate on the other. In the presence of oxalate they were unable to detect less than 0.5 mg. fluorine according to Stone’s procedure.
Quantitative Estimation Reagents required are 300 mg. of purpurin in a liter of ethanol, and 10 N hydrochloric acid, zirconium oxychloride (ZrOCb-SHgO) in 10 N hydrochloric acid containing 0.8 gram of zirconium per liter, and a solution of 19.60 grams of cobalt nitrate [C0(N0g)2-6H20] and 0.132 gram of potassium dichromate per liter water kept in a glass-stoppered
bottle.
Procedure. For the determination of 0.5 to 15 mg. of fluoride the fluoride sample is introduced into an oil-sample bottle of 100 cc. capacity. If it is a solid, 2 cc. of water should be added; if it is a liquid, 2 cc., or a larger volume, made about 10 N with respect to hydrochloric acid together with 2 cc. water may be used. Five cubic centimeters of 10 N hydrochloric acid are added from a buret and then 2 cc. of the purpurin solution from a pipet. Forty cubic centimeters of the cobalt-dichromate solution measured with a graduate are put into a similar oil-sample bottle and used to give standard color for comparison. The zirconium solution in hydrochloric acid is now added from a buret until the color of the solution begins to approach that of the cobalt-dichromate standard. More 10 N hydrochloric acid is then added to bring the total volume just under 40 cc., more zirconium being added till the color matches that of the standard with a total volume of 40 cc. (adjusted by adding sufficient 10 N hydrochloric acid from the buret). The zirconium solution must be added slowly with a shaking so that the titration requires at least 1 to 2 minutes. The number of milligrams of zirconium used is calculated and 1 mg. subtracted from the amount (explained below). The corresponding amount of fluoride present is read in Table II.
ANALYTICAL
120
Table II.
Fluoride Present
Mg.a
Mg. 0.40 0.75 1.20 1.60
1
2 3
4 5 6 7 8
Zirconium Mg.a 10 11 12 13 14 15 16 17 18
2.00
2.47 2.90 3.25 3.70
9 °
Corresponding
Fluoride
Zirconium
Minus
3
Fluoride Present Mg. 4.15 4.65 5.10 5.60 6.12 6.63 7.15 7.73 8.26
to
Zirconium Used
Zirconium
Fluoride Present
Mg,a
Mg. 8.90 9.50 10.10 10.72 11.40 12.08 12.90 13.70 14.53 15.40
19
20 21 22 23 24 25 26 27 28
mg.
EDITION
occur
that 8.75 mg. of zirconium were used in the titration. By interpolation it is found that 7.75 mg. of zirconium
Table III. Fluoride Taken Mg. 0.50 0.50 0.60 0.90 0.90 1.50 1.50 1.50
5.00 5.00 5.00 10.00 10.00 10.00 15.00 15.00 15.00
Titration
Zirconium Used (Uncorrected) Mg. 2.30 2.34
2.50 3.35 3.31 4.93 4.87 4.91
12.78 12.74 12.69 22.00 21.75 22.20 28.8 28.9 28.55
.
of
Fluoride
Fluoride Found Mg. 0.505 0.52 0.575 0.91 0.89 1.57 1.55
Relative
Error %
+1 +4 +
1
-1 4
3
1.56
5.00 4.98 4.96 10.10 9.95 10.22 15.23 15.31 15.01
·
-4
4 0
-0.5 -1
+
1
-0.05
+2 + 1.5 +2 0
Discussion The zirconium solution should be made up in small quantities or standardized frequently, since the chloride has a tendency to precipitate out after several months of standing. The standardization can be made most conveniently against a solution of known fluoride content according to the procedure described above. The purpurin solution in alcohol is nearly saturated. There is no danger of precipitation of dye with fluctuations in temperature. A zirconium-purpurin reagent in fairly strong hydrochloric acid is not stable and should be standardized daily. For quantitative work it was therefore considered more advantageous to keep the solutions of both reagents in separate bottles. The color standard (cobaltdichromate) should be kept in glass-stoppered bottles. If cork stoppers are used, the solution slowly becomes more red by reduction of the dichromate. Correction for Blank. The cobalt-dichromate standard has the same yellow-orange color as a solution containing 0.5 mg. of zirconium, 38 cc. of 10 N hydrochloric acid, and 2 cc. of the purpurin solution. With other amounts of zirconium, solutions are obtained varying in color from yellow to deep pink-violet. In preliminary work it was found that if samples of fluoride were titrated first to one such blank and then to another having a more red color, inconsistent results were obtained if only the weight of zirconium in the blank was subtracted from the total amount of zirconium used. By subtracting twice the weight of zirconium in the blank from each titration value, the ratio of zirconium to fluoride found was nearly the same at the different end points. Thus, by titrating to a yellow-orange color, a zirconiumfluoride ratio of 3.1 and of 3.4 was found if the titration was finished at a red-orange color. In both cases the amount of zirconium in a blank having the same color as the solution at the end point was subtracted from the titration figure. If
2
double the amount was subtracted, the ratios found were 2.50 and 2.48, respectively. Since the stability constants of the various complex compounds between zirconium and fluoride are not known, it is impossible at the present time to base the empirical correction on a more exact basis. The atomic ratio of fluorine to zirconium at the end point increases with increasing amounts of fluoride. With 0.5 mg. of fluoride it was found to be 1.90 increasing to 2.60 with 15 mg. of fluoride (uncorrected for blank). The following are some of the complexes reported to
Suppose
correspond to 3.16 mg. of fluorine. Table III shows that the method gives satisfactory results, even in the titration of small amounts of fluoride of the order of 1 mg.
Yol. 6, No.
(IS): Zr3Fi7
•
It
seems
Zr2Fi3
,
ZrF6~, ZrF6
,
ZrF?
that in more dilute solutions complexes containing
much less fluoride
Effect
,
occur.
Temperature. If the cobalt-dichromate standard is used for comparison, the results are independent of wide fluctuations in temperature. When a color standard is used, made by adding small amounts of zirconium to hydrochloric acid and purpurin, a large temperature effect occurs, the coloi of the standard becoming more yellow with increasing temperature, whereas the color of the titrated solution is not affected by a fairly large change in temperaof
ture. Consequently errors of about 0.5 per cent per degree of temperature difference arise. Therefore, the use of the cobalt-dichromate standard is not only desirable but necessary if accurate results are to be obtained. Acidity. A final acidity of 8.5 N with respect to hydrochloric acid has been chosen. If the acidity is lower than 6 N a cloudy solution results; if it is greater than 10 N, a poor contrast of colors occurs, the color never fully developing. The amount of zirconium used to titrate to the same end point increases with decreasing acidity; however, a slight change of the final acidity of 8.5 N hardly affects the results. Cobalt-Dichromate Color Standards. The mixture selected has a yellow-orange color similar to that of a solution of 0.5 mg. of zirconium in 38 cc. of 10 N hydrochloric acid and 2 cc. of purpurin reagent. Under these conditions the authors noticed the most pronounced changes in color at the end point. This may be a subjective matter and other workers may prefer another color for comparison; therefore a set of various color standards is given in Table IV. Table IV. Co(N03)2-6H20
Mg./40 784 784 784 784 784
cc.
Cobalt-Dichromate Color Standards KíCraO?
Mg.¡40 cc. 5.28 4.00 3.28 2.52 1.96
Zirconium in Blank Having Same Color Mg. 0.50 0.64 0.72 0.80 1.00
Color Yellow-orange
Orange Orange
Orange-pink Pink
In using another color standard than the one recommended, it is necessary to subtract twice the amount of zirconium in the corresponding blank from the titration figure before using Table II. Sharpness of Color Change. The color change near the end point is very gradual. For example, in the titration of 5 mg. of fluoride the solution stayed yellow until 15 cc. of zirconium reagent had been added. With 15.5 cc. the solution was faintly yellow-orange; with 16.5 cc., distinctly yellow-orange; with 17.5 cc., yellow-orange (matched blank); with 18 cc., orange; with 19.0 cc., pink-orange; and with 19,5 cc., pink. By using the comparison solution the end point was certain to 0.2 cc. Sufficient time should be allowed Speed of Titration. for the reaction between fluoride and zirconium to become complete. If the titration is made very quickly too much zirconium is used; the end point is not permanent, and
INDUSTRIAL
March 15, 1934
ENGINEERING
AND
upon standing changes to the reddish side. It is not safe to make a titration in less than 1 minute. If 2 minutes are required in the titration, the solution being shaken several times, good results will be obtained. Determination or Microquantities. The method for titration of fluoride described cannot be used for titration of quantities of fluoride of less than 0.5 mg. A special colorimetric titration procedure is described below for amounts of fluorine between 0.01 and 0.05 mg. The zirconium-purpurin reagent is prepared by adding slowly with shaking a solution of 9 mg. of purpurin in 30 cc. of ethanol to a solution of 0.16 gram of zirconium oxychloride in 6 2V" hydrochloric acid. Add 620 cc. of concentrated hydrochloric acid to the mixture, and make to 1 liter with water. The standard fluoride solution is a solution of sodium fluoride containing 2 mg. of fluorine per 100 cc. of 8 N hydrochloric acid. Measure out 10 ce. of the zirconium-purpurin reagent into each of two test tubes of uniform diameter. Add the unknown sample made up to 2 cc. and 6 N with respect to hydrochloric acid to one test tube. To the other add 2 cc. of 6 A hydrochloric acid. Add about 2A cc. of the standard fluoride solution from the microburet to the second tube, which gives an orange color. Then add the same fluoride solution to the other test tube and enough 8 N hydrochloric acid so that the colors match when the volumes are the same.
The difference in the amount of standard fluoride added to both test tubes corresponds to the amount of fluorine in the unknown. Thus, if 2.4 cc. were used for the blank and 1.7 cc. for the sample, the fluorine content of the unknown is 0.014 mg. The end point can be recognized within 0.1 cc. of the standard fluoride solution—that is, the method is accurate within 0.002 mg. of fluoride. Hence, the amount of fluoride in the sample should be 0.01 mg. or larger in order to get an accuracy of at least 10 per cent. The upper limit of fluorine in the sample amounts to 0.05 mg. according to the procedure described. Larger quantities can be determined if larger tubes and more of the zirconium-purpurin reagent are used. Another alternative which has not been investigated is the use of a reagent containing more zirconium. Experimental results are given in Table V. Some titrations were made in the presence of substances not expected
(2.4
-
1.7) 0.02
Table V.
Colorimetric Titration
of
Fluoride
(0.01 to 0.05 mg.)
Fluoride Taken Mg. 0.005 0.005 0.010 0.010 0.040 0.040 0.010 0.040 0.010 0.040 0.010 0.040 0.010 0.040 0.010 0.040
Interfering
Substance Added (20 mg.)
Calcium acetate Calcium acetate Potassium iodide Potassium iodide Sodium sulfite Sodium sulfite Sodium nitrate Sodium nitrate Sodium acetate Sodium acetate
Substances.
stances forming chlorine
Fluoride
Found Mg. 0.006 0.004 0.011 0.010 0.040 0.038 0.010 0.042 0.009 0.042 0.010 0.038 0.009 0.040 0.010 0.040
Error
Table VI.
Present
Mg.
NaAc, NaBr, NaCl,
5
NaAc, NaBr, NaCl,
NaS20g, K2Cr207, 50 mg. of each
5 5 5
5 5
5 5 5 2
Na2S20s, 20 207, 50 mg. of each KH2PO4, 500 mg. A1CU, 200 to 500 mg. HgBOa, 250 mg. HgBOg, 10 mg. NaNOa, 500 mg. NaNOg, 500 mg. KI, 500 mg. KClOs, 200 mg. Na2C204, 500 mg.
KH2PO4, AlCls, NaAc, NaBr, NaNOg, NaNOs, 50 mg. of
0.1
NaaCsO*, KH2PO4, KC1, 500 mg. of
0.1
NaN02, NaNOg, KCIO2, 50 mg. of
-20 0
-5 0
+5
-10
+
5
0
-5 -10 0
0 0
Colored substances,
with hydrochloric acid, substances
precipitating with zirconium (phosphates) or forming more or less stable complexes with fluoride (aluminum, boric acid), and in addition, sulfates, oxalates, and nitrites interfere with the titration. Successful titrations have been made in the presence of nitrates, sulfites, acetates, iodides, bromides, zinc, calcium, barium, magnesium, and alkali salts. Oxidizing substances can be reduced with sodium sulfite before the titration. Aluminum ions and boric acid tend to form complexes with fluoride. Since these complexes are less stable than the zirconium complex in the strong acid
(11) (12) (13)
(14)
of
Remarks
60, 51
Collected in water
97, 98, 100, 101 97, 100 (57), 98, 98, 99, 100
Collected Collected Collected Collected Collected
1, 7
64, 80 97, 98 95, 97, 99, 95,
Distillate Distillate Distillate Distillate Distillate
96
98, 102 99 98, 100
in NaOH in NaOH in NaOH in NaOH in NaOH with sulfite with sulfite with sulfite with sulfite with sulfite
(56), 94, 97, 98, 101
Distillate with sulfite
95, 95
Distillate with sulfite
100, 105, 95
Distillate with sulfite
Literature
10
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
Presence
%
5
5
in the
Fluoride Recovered
stances
ide
Taken
%
0
Determination of Fluoride Various Substances
Other Sub-
Fluor-
+ 20 +
121
medium, titrations can be made in the presence of small amounts of these substances. In the titration of 2 mg. of fluoride 7.50 cc. of reagent were required; in the presence of 10 mg. of aluminum, 7.50; of 15 mg., 7.2; of 20 mg., 7.0; of 30 mg., 6.1; and of 50 mg., 5.5 cc., respectively. With the same amount of fluorine and 1 to 10 mg. of boric acid the results found were about 5 per cent high. The complex formation does not interfere yet or at any rate is overshadowed by a tendency of boric acid to react with the zirconium-purpurin reagent. With 100 mg. of boric acid the results were 33 per cent low. Phosphate interferes strongly; when as little as 1 mg. is present, it becomes impossible to titrate a 1-mg. sample of fluoride, owing to the cloudy appearance of the solution. The distillation as HsSiFg according to the method of Willard and Winter (14) can be used to separate fluorine from these interfering substances, or the fluorine can be distilled off as silicon tetrafluoride by the well-known method described by Daniel (7), Adolph (1), Reynolds (10, 11), Cesares (6), and others. Using the latter method, a number of determinations were made, using the simple apparatus described above. (Further details are given in the thesis of Stansby.) The results are tabulated in Table VI. Good results were obtained only with an extremely slow rate of heating during the distillation, a point not brought out in the literature.
=
to interfere.
CHEMISTRY
Cited
Adolph, A. H., J. Am. Chem. Soc., 37, 2500 (1915). Alimarin, I. P., Z. anal. Chem., 81, 8 (1930). Armstrong, W. O., J, Am. Chem. Soc., 55, 1741 (1933). Boer, de, and Basart, Rec. trav. chim., 44, 1071 (1925). Boer, de, and Basart, Z. anorg. allgem. Chem., 152, 203 (1926). Cesares, J., Anales soc. españ.fís. quím. (technica), 27, 290 (1929). Daniel, Z. anorg. Chem., 38, 254 (1904). Koone, B., Chemist-Analyst, 20, No. 4, 14 (1931). Pavelka, Mikrochem., 6, 149 (1928). Reynolds, D. S., and Jacobs, K. D., Ind. Eng. Chem., Anal. Ed., 3, 366, 371 (1931). Reynolds, D. S., Ross, W. H., and Jacobs, K. D., J. Assoc. Official Agr. Chem., 11, 225 (1928). Stone, I., J. Chem. Ed., 8, 347 (1931). Venable, F. P., “Zirconium and Its Compounds,’’ Chemical Catalog, 1922. Willard, . H., and Winter, O. B., Ind. Eng. Chem., Anal. Ed., 5, 7 (1933). z
June 24, 1933. Presented in part before the Division of Physical and Inorganic Chemistry at the 81st Meeting of the American Chemical Society, Indianapolis, Ind., March 30 to April 3, 1931. From a thesis submitted by Maurice E. Stansby to the Graduate School, University of Minnesota, in partial fulfilment of the requirements for the degree of Master of Science. A complete bibliography and literature review is given in the thesis. Received
