t50
tive maxima, SPSA, although an anionic soap, can s u p p r e s both the positive (Pb+2, copper-biuret complex, copper-glycine complex, and cystine) and the negative (Cd14-2, C O + ~ , X i L 2 ,Co+2-Si+2mixture) maxima.
n‘
ACKNOWLEDGMENT
The authors are thankful to C.S.I.R. India for the award of a fellowship to one of us (R.H.) to carry out this work. Figure 1.
Typical polarogram LITERATURE CITED
1 division = 0.2 volt. Each curve starts o t 0.2 volt 0.0025M Cdlz in 0.2M KI Concentration of SPSA in 1 . None 2. 4.9 10-4~
(1) Haworth, R. C., Mann, F. G., J . Chem. SOC.1943, 603.
(2) Kolthoff, I. Lingane, J. J., “Polarography,” 2nd ed., p. 509, Interscience, S e w York, 1952. (3) Lingane, J. J., Kerlinger, H., IXD. ENG.CHERI.,ANAL.ED. 13,i 7 (1941). (4) Stirton. A . J., Peterson, R. F., Groggins, P. H., I n d . Eng. Chem. 32,
x 7.39 x 12.1 x
1 o-’w 10-4~ 5. 16.9 X 10-‘M 6. 19.0 X lO-‘M 7. 23.8 x 1 0 - 4 ~
3. 4.
adding SPSA (19.2 X 10-4L11)thi- could be eliminated and a reversible n ave for the complex with E l / , = -0.7 volt n-as obtained.
1136 (1940).
The use of SPSA has a further advantage. Although cationic soaps help to suppress negative maxima, nhereas anionic soaps are used to eliminate posi-
WAHIDE. ~ I A L I K RIZWANUL HAQUE Department of Chemistry Aligarh Muslim University ALIGARH, I N D I A
RECEIVEDfor review May 6, 1960. Accepted August 1, 1960.
Discussion of “Steam Distillation of Fluorine from Perchloric Acid Solutions of Aluminiferous Ores” Sm: I n a recent paper Fos and Jackson ( 1 ) concluded that in the TKllard-\Tinter distillation of fluoride (8) silicon is essentially not distilled, and implied that the interference of aluminum(II1) in the same type of distillation is circumvented only by fusion of t,he sample or by double distillation. On page 1660 ( 1 ) the statements were msde t h a t “In the steam distillation process, . . . silica is precipitated in hydrated form in the solid phase, and the fluorine is distilled as the tetrahydrate of hydrogen fluoride . . . and it is evident that fluorine is distilled (Willard-Winter method) mostly as a hydrate of hydrogen fluoride or hydrofluoric acid.” If fluoride is distilled largely as hydrogen fluoride as stated. i t t’hen is obvious that little or no silica should be in the distillate resulting from a KillardVinter distillation. However, previous literature (3, 7) has shown that the amount of silica in the distillate is substantial. -1 Federal Bureau of Mines rtport’ (?)> page 12, tables 11 and 12, slio~\-cdqiiantitative data relating fluor-
ide taken for distillation and silica in the distillate. Fluoride Taken, hIg. 100 20 12
4
Silica (Calculated a5 SiOz) in Distillate, 1Ig. 61 t o 6T 8 4 0.3
Only when fluoride was very low did the silica in the distillate become or approach zero. Even when borate was present nearly the same amount of silica \vas in the distillate as shown above ( 7 ) . Harel, Herman, and Talmi (3) demonstrated that b y determining the silica in the distilling flask and in the distillate, quantitative recovery of SiO, was obtained. Harel, Herman, and Talmi added a known amount of SiOz as sodium silicate solution, then deducted the added SiO, from the total silica. I n this manner they showed that silica was not introduced from the glassware; that silica could be quantitatively determined; and that a
substantial amount of silica was in the distillate. The coinpound of fluoride actually distilled in the Killard-Winter distillation is of interest. I n 1923 Jacobson ( 5 ) proved that “H2SiF, is a nonvolatile acid which cannot exist . . . in the vapor state.” The data from references (3,7 ) , showing substantial amounts of silica in the distillate, indicate SiF4 HF as the probable distilling forms of fluoride. TJ’hen the quantity of fluoride distilled was 100 mg., SiF4 must have been the predominant form. Fox and Jackson state that measures that have been proposed to overcome the interference of aluminum and silica with fluorine distillation fall into two categories. One is fusion as in the Berzelius method, or use of zinc oxide in the fusion mixture, as per Shell and Craig (6) and Hollingsworth (4). “The other procedure involves double distillation.” Fox and Jackson did not consider the most effective and perhaps easiest method of preventing aluminum [A1 (III)] interference-the use of 2 to 5 nil. of 85% H3P04 ( 2 , 7 ) in the per-
+
VOL. 32, NO. 1 1 , OCTOBER 1960
* 1529
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.
