chloric acid distillation. References ( 2 , 7) clearly showed that the 2 to 5 ml. of HsPO4 eliminated the interference of large amounts of A1 in the distillation of fluoride. Also, the combination of ZnO in the fusion and H8POIin the distilling acid was shown to eliminate both Al(II1) and Si(1V) interference in fluoride distillations ( 2 ) . The 2- to 5-ml. additions of HaPOl to the perchloric acid were satisfactory in the determination of macroamounts of
SIR: I n our article, as the title implies, we were discussing steam distillation of fluorine from perchloric, not phosphoric, acid solutions. We did not undertake to make an exhaustive survey of all the analytical methods. Shell and Craig's procedure of adding phosphoric acid to overcome aluminum interference during the distillation only enhances the problem of phosphorus interference during the subsequent titration of fluorine in the distillate. There are such things as compensating errors, but we are not in a position to advance this argument, since we do not have any specific information on this subject. We did, however, rely upon the evidence of others, notably that of Reynolds, who concluded that phosphoric acid is not suitable for the distillation of fluorine [J. Assoc. O$ic. Agr. Chemists 18, 108 (1935); ISD. ESG. CHEX, ANAL. ED. 11, 21 (1939)]. Our own experience is in line with Reynolds' observations and conclusions. I n fact, the close control of the distilling acid temperature a t 125' C. instead of 135' or above, was to avoid the distillation of phosphorus along with fluorine. The evidence of silica in their distillates cited by Dr. Shell is in line with the interpretation given by Fox and Jackson for the H2SiF8-H20 system (page 1660). There Kas no denial that silicon (probably as SiFd gas) was evolved under the conditions described by Shell and Craig, It was, and still
fluoride; whether applicable to microamounts was not determined. LITERATURE CITED
(1) Fox, E. J., Jackson, R.4.,ANAL. CHEX 31,1657-62 (1959). (2) Grimaldi, F. S., Ingram, Blanche, Cutitta, Frank, Ibid., 27,918 (1955). (3) Harel, S., Herman, E. R., Talmi, A., Ibzd., 27, 1144 (1955). (4) Hollingsworth, R. P., Ibid., 29, 1130 (1957).
(5) Jacobson, C. A,, J. Phys. Chem. 27, 761 (1923). ( 6 ) Shell, H. R., Craig, R. L., ANAL. CHEX26,996 (1954). (7) Shell, H. R., Craig, R. L., U.S. Bttr. Mznes, Rept. Invest. No. 5158, 30 pages (1956). (8) Willard, H. H., Winter, 0. B., IND. EXG.CHEW,ANAL.ED.5 , 7 (1933).
H. R. SHELL
Bureau of Mines P. 0. Box 217 Norris, Tenn.
100
IOi
9i 81
71
0
20
40
80 T i m e , Minutes
60
100
120
140
Steam distillations of fluorine as 125' C. from wet-process phosphoric acid compared with distillations of fluorine from perchloric acid solutions of aluminum fluoride and calcium fluosilicate
is, our contention that i t was not distilled as H2SiF6. As to the contention that phosphoric acid will overcome the interference of aluminum in steam distillation of fluorine, the accompanying - - - -graph shows some results we have obtained recently in a study of sludge formation in wetprocess phosphoric acid in which steam distillation from aluminiferous wet-
process acid was compared with the steam distillation of fluorine from perchloric acid solutions of calcium fluosilicate and aluminum fluoride. Readers may draw their own conclusions from the data shown. slaterials Section EDWARD J. Fox Agricultural Research Service Beltsville, Md.
Photometric Determination of Boron by Solvent Extraction Using Monomethylthionine SIR: The successful modification and application to steel analysis ( 2 ) of Ducret's methylene blue-boron method ( 1 ) led to a study of other thionine derivatives. Of the commercially available compounds, Azure C (monomethylthionine) proved to be superior to methylene blue. Except for the substitution of Azure C (National Aniline), the reagents, apparatus, and procedure are essen1530
ANALYTICAL CHEMISTRY
tially the same as reported for the methylene blue method (2)- A 0.1gram sample is dissolved in 10.0 ml. of 2.5-V sulfuric acid and any residue is filtered off, ignited, fused with 1 gram of Na2C03, and dissolved in the filtrate plus 4.0 ml. of 2.5N H2S04, Then 5.0 ml. of 5y0 HF are added, 2 hours are allowed for the boron fluoride formation, the oxidation state is adjusted by titration ryith 0.1M K1lnO4 followed
by the addition of 2 to 3 ml. of 4yo ferrous ammonium sulfate solution, and the volume is brought to 50.0 ml. A portion, 10 ml., of 0.002 or 0.005M Azure C is added and the complex extracted into lI2-dichloroethane or mixtures with lJ2-dichloropropane or carbon tetrachloride. The absorbance a t 658 mp is used with a calibration curve to measure the boron concentration.
I20
I
I
-
0 la2 - D l C H L O R O E T H A N E 0 I I I , 2 - O I C H L O R O E T H A N E : 1.2-OlCHLOROPROPANE A 132-DICHLOROPROPANE X -20% CCL4 IN 1 . 2 - D I C H L O R O E T H A N E
1----
-
-----IO
-0002-M
MMT METHYLENE BLLE 0001-M
1.00
BORON RlAAGENT B L A N K
REAGENT
BLANKS
Y O F BORON
Figure 2. 560
580
620 640 WAVE LENGTH,
600
660
680
70C
mp
“0°
Figure 1. Spectral absorbance curves of the MMT-B complex in different solvents Aqueous phase, 60 ml. 0.01 7 0 HF; organic phase, 25 ml.
The absorbance maximum for the monomethylthionine (MMT) boron fluoride complex in several organic solvents and mixtures occurs a t 658 my (Figure 1). Application of the continuous variation method (3) showed a 1 to 1 MMT:B complex, but at least a 5 to 1 molar excess of RILIT over boron should be used for analytical work to ensure complete formation and maximum sensitivity in the extraction of the complex. As with methylene blue, alloying elements in the ranges commonly found in steel give no interference. This work was carried out to eliminate, if possible, two disadvantages of the methylene blue procedure-viz., the high reagent blank which makes dilution of the extract necessary and the relatively narrow concentration range, 0.2 to 25 y of B, which requires extreme aliquoting of high boron solutions. All of the dyes investigated (Table I), proved applicable to some extent for the boron determination if coupled n-ith the right organic solvents. The use of Azure C n-ith 1,2-dichloroethane and mixtures of this solvent n-ith 1,2dichloropropane or carbon tetrachloride eliminated both the blank and concentration range problem. From 0.1 t o 200 y of B can be determined without diluting or aliquoting. Suggestec‘ solvent mixtures for different concentration ranges are given in Table 11.
-
Table I,
Comparison of methods
I I DICHLOROETUANE
.80
-
W
Dyes Investigated in This Study
Dye
DICHLOROPROPANE
0005-M M M T
Composition
Thionine Azure C Azure A Azure B Methylene blue Toluidine blue 0 New Methylene Blue K’ Methylene green
3,7-Diaminophenothiazonium chloride AT-Methylthionine N-Dimethylthionine K ,A‘ ’-Trimethylthionine A7,X’-Tetramethylthionine 8-Methyl-N-dimethylthionine N,AT’-Diethy 1-4,6-dimethylthionine 6-Xtro-N,Nf-dimethylthionine
0
20
40
r
80
60
I
OF BORON
Figure 3. Calibration mixed solvents
curve
with
The greater sensitivity of LINT, with its lower reagent blank, is shown in Figure 2. I t s suitability for wider boron concentration ranges is shown by the typical calibration curve in Figure 3. LITERATURE CITED
(1) Ducret, L., Anal. Chim. Acta 17,
Table 11. Suggested Solvent Mixtures for Different Concentration Ranges
Range, Boron
y
0-20 1-100 1-200
Solvent 1,2-Dichloroethane
1 to 1 Dichloroethane: dichloropropane or 15%
carbon tetrachloride in dichloroethane 25% Carbon tetrachloride in dichloroethane, or 1,2dichloropropane
213 (1937). (2) Passtor, L. C., Bode, J. D., Fernando, Q., ANAL.CHEM.3 2 , 2 7 7 (1960). (3) Vosburgh, 7FT. C., Cooper, G. R., J. Am. Chem. SOC.6 3 , 4 3 7 (1941). LASZLO C. PASZTOR J. DANIELBO DE^ Graham Research Laboratory Jones & Laughlin Steel Corp. Pittsburgh 30, Pa. 1 Present address, Bell Telephone Laboratories, Murray Bill, S . J. Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy. Pittsburgh, Pa., March 1960.
VOL. 32, NO. 1 1 , OCTOBER 1960
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