I-VDUSTRISL d S D ESGISEERISG CHEMISTRY
July 15, 1930
the mark for 20” C. is placed directly below the end of the vertical line for zero correction, and the other m a r k are then located with respect to this one. The lines parallel to the line for zero correction are spaced equidistant from each other on the arcs. Figure 3 indicates the manner of handling the morable indicator, the position being shown both for 30” and 20” C. I n using it one brings the straight portion of the irregular edge to the point indicating the orking temperature and then locates the point of intersection of the irregular edge with the arc for the indicated volume, as read on the buret. On moving from this point, on a line parallel with the line for zero correction, to the arc for 50 nil. one obtains the proper correction to apply. I n addition to giving a combined correction, this proposal has the merit of ready adaptability for different burets and different wlutions.
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Literature Cited (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (171 (15)
Blasdale, “Fundamentals of Quantitative Analysis,” p. 278 (1928). Couvee, Chem. W e e h b l a d , 23, 550 (1926). Fales, “Inorganic Quantitative Analysis,” p. 114 (1925). Farnsrvorth, “Theory and Technique of Quantitative -4nalysis,” p. 74 (1928). Foulk, “Quantitative Chemical Analysis.” p. 100 (1914). Friedman and L a l l e r , IND. Esc. CHEM.,Anal. E d . , 2, 54 (1930). Kolthoff-Furman, “Volumetric Analysis,” Vol. 11, p . 27 (1929). Mahin, “Quantitative Analysis,” p. 178 (1924). Osaka, Mem. Coll. Sci., Krololmperial Uniu., 4, 113 (1920). Popoff, “Quantitative Analysis,” p. 56 (1927). Schloesser, Chem.-Zlg., 29, 510 (1905), Schoorl, Chem. Ti-eekblad, 23, 581 (1926). Schulze, Z . a 7 d Chem., 21, 167 (1882). Smith, “Quantitative Analysis,” p. 46 (1924). Sutton, “Volumetric Analysis,” p. 26 (1924). Talbot, “Quantitative Chemical Analysis,” p. 192 (19241. Treadwell-Hall, “Analytical Chemistry,” Vol. 11, 461 (1928). Washburn, J . A m . Chem. Soc., 3 0 , 31 (1908).
Spectroscopic Detection of Fluorine’ Jacob Papish, L. E. Hoag, a n d W. E. Snee DEPARTYEKT O F CHEMISTRY, CORKELLUKIVERSITY, ITH.ACAS . P
An indirect spectroscopic method for t h e detection LUORISE, like many give a potential drop of aliout of fluorine is described. I t consists i n subjecting a 60 volts and from 8 to 10 aniof the other non-metallic mixture of a fluoriferous substance with a salt of calelements, yields no priperes. The lower electrode, cium t o arc excitation and examining t h e spectrum fgr which held the sample, n a s inary lines of series in the opbands of calcium fluoride. The band a t lambda 5291 A. the anode. X glass spectrotical spectral range. Because is t h e most persistent; i t is visible when 0.01 mg. of graph of the constant-deviaof this the detection of fluorfluorine is present in t h e zone of excitation, though i n tion type was Pmployed. On ine, especially in small quangeneral practice i t is difficult t o detect quantities less numerous other occasions tities, is out of question if the t h a n 0.02 mg. However, substances which contain quartz spectrographs were chemist were to depend on the m i n u t e quantities of fluorine can be subjected t o a conused; the spectrograms in spectrum of the element in centration by distilling off t h e fluorine as hydrogen Figure 1 TT-ere obtained with a the atomic state, since the fluoride, collecting i t i n a solution of limewater, a n d chemist’s work is limited to Cornu-type quartz spectroarcking t h e calcium fluoride t h u s produced. g r a p h . 2 The spectrogram the optical range. It Fvas JIitscherlich (6) &s- produced containedlines who observed that the alkali-earth halides yield band and bands among which the characteristic band due to calspectra due to compounds in a n excited state in the flame, cium fluoride (at X 5291 A.) stood out prominently. The experiment was next varied by arcking mixtures of and Fabry ( Z ) , Rosch ( 7 ) , and Dufour ( I ) examined the band spectrum of calciuni fluoride. K a p e r (4) reduced alkali fluorides with calcium salts other than the carbonate. the values obtained by these three investigators to a com- Calcium nitrate, calcium chloride, calcium sulfate, and nion scale for purposes of comparison and tabulated the tricalcium phosphate were used for this purpose, and in each bands in the order of their maxima. These bands were case the band spectrum of calcium fluoride was observed. mentioned by Mott (6)as a n aid in recognizing calcium as well Similar results were obtained with the high-frequency, conas fluorine. They lie in the lower and middle frequency range densed spark. of the visible spectrum and they can be observed with the Applications eye as well as photographed on suitable plates. They vary in intensity and persistence. The most persistento band, The spectroscopic observations just described served as which is green in color, has its maximum a t X 5291 A., and a basis for the deduction that, whenever a fluoriferous subit fades out in the direction of the less refrangible end of the stance is vaporized in the arc or in the spark together with a spectrum. I t is produced whenever calcium fluoride is sub- calcium compound, the chances are favorable for the formajected to arc or spark excitation. But it is not necessary tion of calcium fluoride, or rather of that variety of calcium to start with calcium fluoride as such in order to obtain this fluoride which under excitation yields the characteristic band characteristic band. fluoriferous substance when mixed spectrum. It is evident that this spectral reaction can be with a compound of calcium and arcked or sparked will yield adapted for the indirect identification of fluorine. To check the band in question. This was demonstrated in the follolv- the applicability of the method the following experiments were ing manner. performed. Experimental A number of fluorine-bearing compounds were chosenA few iiiilligranis of potassium fluoride were ground with namely, ammonium fluoride, sodium fluoride, cupric fluoride, about an equal quantity of precipitated calcium carbonate. potassium-beryllium fluoride, barium fluosilicate, lead fluoThe mixture v a s placed between graphite electrodes, sub- silicate, potassium fluoplumbate, potassium fluogermanate, jected to arc excitation, and the spectrum photographed. potassium fluotitanate, sodium fluoborate, and potassium The direct-current arc was used with suitable resistance to fluocolumbate. Each compound was ground intimately
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Recei\ ed April 10, 1930.
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Built by Bausch and Lomb Optical Co , Rochester, S P.
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ANALYTICAL EDITION
VOl. 2,
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with precipitated calcium carbonate, which previous spectroscopic examination had shown to be free from fluorine. The mixtures were examined spectrographically and in allocases the characteristic band of calcium fluoride a t X 5291 A. was observed as well as the other bands. (Figure 1) The method was extended to naturally occurring minerals. The case of fluorite and apatite is of course obvious. The same is true of phosphate rock, d i i c h approaches apatite in composition; the fluorine in it can be detected by arcking a small quantity of the so-called raw phosphate and even of acid phosphate. Topaz is known to be fluoriferous. K h e n its
Ten grams of calcium carbonate were dissolved in acetic acid. The solution was diluted to 100 cc. and the calcium content was determined in an aliquot portion by precipitation with ammonium oxalate and titration against a standard solution of potassium permanganate. The concentration of the solution was adjusted so that 0.1 cc. contained calcium equivalent to 10 mg. of calcium carbonate. A solution was made of 2.211 grams of sodium fluoride in 100 cc. of water. The fluorine content was determined in a n aliquot portion by precipitation as PbFCl according to the method of Starck (8), and the concentration adjusted so that 0.1 cc. containpd 1 mg. of fluorine. From this stock solution other solutions were made u p which contained 0.1,0.05,0.04,0.03,0.02,0.01, 0.009, and 0.008 mg. per 0.1 cc. One-tenth cubic centimeter of each solution was placed on a fresh graphite electrode with the aid of a calibrated capillary pipet. The electrode was heated gently n i t h a Bunsen flanie and 0.1 cc. of the calcium acetate solution TTas added. Heating TTith the flame n a s repeated till the electrode was dry. The arc discharge was passed and the spectrum photographed.3 The results as relaJing to the band of calcium fluoride a t X 5291 A. are given in Table I. The amount of calcium actually used in each case \\as considerably in excess of that required for the conversion of fluorine into calcium fluoride. As seen from Table I, the intensity of the band decreases x i t h the decrease of concentration of calcium fluoride under the conditions described. I n general practice m-here fluoriferous substances of a more complex nature are examined this limit 4 X 5291 A. is seldom reached, but quantities in the neighborFigure 1-Arc Spectrograms Obtained with (a! S o d i u m Fluoride, ( b ) C a l c i u m hood of 0.02 mg. are recognizable. Carbonate, fc) Calcium Fluoride, a n d ( d J a Mixture of S o d i u m Fluoride a n d
Calcium Carbonate
arc spectrum is examined, the presence of the halogen is not detected. As a matter of fact the spectrum of topaz in the optical range is identical TT ith that of kyanite and of sillimanite. However, when calcium earlmiate was used in connection with topaz, the presence of fluorine n-as established by the indirect spectroscopic method. In the same manner fluorine was detected in tourmaline, cryolite, lepidolite, amblygonite, leucophanite, herderite, yttrofluorite, chondrodite, and meliphanite. of Calcium Fluoride Band a t X 5291 1. IXTENSITYOF CALCIUM FLUORIDE BAND
Table I-Persistence FLUORINE Mg. 1 0.1 0.05 0.04 0.03 0.02 0.01 0.009 0 008
AT
X 5291
A.
Very intense Intense Intense Intense Faint Fainter than preceding Very faint Doubtful Absent
Sensitivity of Test
The sensitivity of a spectral test depends on a number of factors. Other things being equal, the intensity of a line or band will be found to vary with the quantity of excited material, a t least up to a certain point. Sensitivity is usually expressed as the least amount of the element in question necessary to produce a recognizable line or band. I n the case of fluorine it refers to the least weight of fluorine as calcium fluoride which wheno excited in the arc will produce the persistent band a t X 5291 A. Since the solubility of calcium fluoride in water is very lom-, use was made of solutions of calcium acetate and sodium fluoride of known concentration.
Concentration of Fluorine
The spectroscopic test for fluorine was applied to teeth and bones of rats and pigs. The samples 1%-ereashed in a muffle furnace, and sinal1 quantities of the ashes, usually 10 mg., were arcked and the spectrograms examined. I n the case of teeth t,he presence of fluorine was always observed. The same was true of many bone samples, but in the spectrograms of some of these the calcium fluoride band was not discernible, and the ashes were subjected to treatment for the concentration of fluorine. Five grams of bone ashes Tvere placed in a small platinum retort and covered v i t h 15 cc. of sulfuric acid of about 25 per cent concentration. The platinum receiver, which contained a solution of limewater, was kept cool with a freezing mixture of ice and salt and the retort was heated with the aid of an oil bath, the temperature being kept below 200" C. When 10 cc. of distillate were collected, the content's of the receiver %-ere evaporated to dryness and the residue was tested spectrographically. I n all cases the band indicating the presence of fluorine was intense. Literature Cited (1) Dufour, Conapt. r e n d . , 146, 118 (1908). (2) Fabry, Aslrophys. J . , 21, 336 (1905). (3) Hawley, I N D . EXG.CHEM., 18, 573 (1926). (4) Kayser, "Handbuch der Spektroskopie," Val. V, p. 260, Leipzig, 1910. ( 5 ) lfitscherlich, A n n . Phys. Chem., 121, 467 (1862). (6) M a t t , Trans. A m . Elecfrochem. S o c . , 37, 665 (1920). (7) RGsch, Z . wiss. Phot., 4, 384 (1906). (8) Starck, 2.a n o r g . Chem., 70, 173 (1911). J D. C. Ortho plates manufactured by Eastman Kodak Company were used. Plates sensitive t o the green were also tried, but were not found superior to the ordinary variety
