766
ANALYTICAL CHEMISTRY chamber. Column 2 lists the corresponding equilibrium temperatures before the liquid was withdrawn, and column 3 lists the purities calculated by means of the melting point equation. Column 4 lists the actual yields and column 5 lists the percentage of the theoretical yield obtained based on Raoult’s law and eutectic composition. When the vanes were not compressed, larger quantities had to be melted before each withdrawal as the amount which could be removed without squeezing
Table I. Progress of Purification of Iso-octane with Compressing of Vanes Liquid Withdrawn,
MI.
.
0 28 28 36 23
36 30 0 0
Equilibrium Temp., OK.
Fraction of Liquid
161.05 163.36 163.76 164.15 165.48 165.71 165.71 165.71 165.71
0.10 0.10 0.10 0.115 0.101 0.095 0,050 0.141 0.347
Purity Calod. from Temp
%
94.4 99.1 99.4 99.40 99.91 100.00 100.00 100.00 100.00
Purity Calcd. from Washing,
%
...
96.0 97.6 99.6 99.8 99.93 99.998 99.998 99.998
calculated by means of the melting point equation, of the material remaining in the melting chamber (this includes the solid and liquid portions). Column 5 lists the purities calculated by the batch theory of washing, assuming all of the impurity to be dissolved in the melt. The amount of liquid remaining after withdrawing the melted liquid (as completely as possible) was estimated from the difference between the amount of liquid melted, as determined from the added energy, and that withdrawn into the receiving flask. Column 6 lists the actual yields (in percentage of the original charge) and column 7 lists the percentage of the theoretical yield obtained. The theoretical yield was estimated from a eutectic diagram calculated assuming the applicability of Raoult’s law and the absence of solid solution. A lower purity is calculated by batch theory of washing because the actual operation is effectively continuous, the descending ’ washings occupying a relatively small volume. For this reason the purity calculated by means of the melting point equation is considerably more accurate than that calculated by the theory of washing. That equilibrium is reached with respect to composition is indicated by the fact that the equilibrium temperature did not change with time. Moreover, after the equilibrium temperature indicated that all impurity had been removed, melting half the remaining material produced no rise in the equilibrium temperature (see the last three entries in Table I). The second purification was effected by keeping the vanes stationary in the expanded position. The results are listed in Table 11. No attempt was made to apply the theory of washing, since the melt no longer made contact with all of the crystals. Column 1 lists the amount of liquid withdrawn from the melting
Theoretical ‘70
100.0 94.4
88.8 81.6 77.0 69.6 64.0 64.0 64 0
.. .. .. ..
%
96 87 80
80 80
was greatly reduced. Comparison of the two tables shows that the purification efficiency is increased by a factor of about 3 a t the 99.98% level of purity when the compressible vane system is used. The time for equilibration was about 2 hours when the vanes were immobilized, as compared to 15 to 20 minutes when the vanes were activated. The last fraction in the purification without compressing the vanes had not come to equilibrium even after 3 hours.
Table 11. Liquid Withdrawn,
MI.
Purification of Iso-octane without Compressing of Vanes Equilibrium Temp.,
K.
Purity Calcd. from Temp., %
Yield,
5%
Theoretical Yield Obtained, %
ACKNOWLEDGMENT
The authors wish to thank the Phillips Petroleum Co. for the financial help which made this work possible. LITERATURE CITED
(1) Aston, J. G., and Mastrangelo, S. V. R., ANAL.CHEM.,22, 636 (1950). RECEIVED for review August 22, 1953.
Accepted January 18, 1954.
Estimation of Fluorine in Biological Material P. VENKATESWARLU and D. NARAYANA RAO Department of Biochemistry, Medical College, Trivandrum, M i a
I
N CONNECTION with the estimation of fluorine in blood, Smith and Gardner ( 8 ) drew attention to the loss of fluorine as a volatile iron fluoride when the blood is ashed preparatory to the Willard-Winter distillation (3). For this reason, they adopted a preliminary sulfuric acid distillation (before ashing) to free fluorine from the iron. To obtain reliable results in the case of other biological materials, i t was also found that a preliminary distillation is necessary owing to the almost universal occurrence of iron in plant and animal tissues Silica in plant materials also interferes with fluorine recovery (1). This interference was reduced by preliminarv distillation of the unashed sample or by fusion of the lime-ashed sample with qoclium hydroxide before distillation of the fluorine from perchloric acid. . i n earlier observation (4)made in these labora-
tories, to the effect that magnesium oxide is a good adsorbent for the fluoride ions, considerably facilitated the fluoride analytical procedure which was thereby rendered more rapid. PROCEDURE
One-half gram of material is submitted to Willard-Winter distillation, employing sulfuric acid. The distillate, which is kept just alkaline to phenolphthalein, is brought to boiling, 0.2 gram of light magnesium oxide is added, and the boiling 1s continued for 5 minutes more. The magnesium oxide with the adsorbed fluoride is separated by centrifugation or filtration and eubmitted t o the Willard-Winter perchloric acid distillation in the presenrr of harium and silver perchlorates t o withhold the interfering sulfate and chloride ions. The fluoride in the distillate is determined by titration by the Smith and Gardner technique ( 2 ) .
V O L U M E 2 6 , NO. 4, A P R I L 1 9 5 4
767
RESULTS
The fluorine content of a sample of tea as determined by the present method was 180 p.p.m., whereas the values obtained by the conventional ashing method ranged from 30 to 120 p.p.m., depending on the temperature of ashing, period of ashing, the fixative, and the quantity of the fixative employed. The method is now being extended to other biological materials,
sity of Minnesota for advice and for assistance in preparation of the manuscript. LITERATURE CITED
Remmert, L. F., ANAL.CKIEM., 25, 450 (1953). (2) Smith, F. A., and Gardner, D. E., U. S. Atomic Energy Commission, Unclassi8ed Document UR 36 (1948). (3)
Willard, H. H., and Winter, 0. B.. IND.ENG.CHEM.,ANAL.ED., 5.7 (1933).
(4) Venkateswarlu, P., and Narayana Rao, D., Indian J . Med. Research, 4 1 , 4 (1953).
ACKNOWLEDGMENT
The authors are indebted t o ITr.D. Armstrong of the Univer-
RECEIVED f o r review September 12, 1953. Accepted January 14, 1954.
Spect rochemical St udy of Gravimet ric Procedure For Barium, Strontium, and Calcium P. R. WILKINSON and J. A. GIBSON, JR.,
Department of Chemistry, W e s t Virginia University, Morgantown,
W. Va.,
and
A. J. W. HEADLEE, W e s t Virginia Geological Survey, Morgantown, W . V a .
G
RAVIMETRIC methods for the separation and determination of barium, strontium, and calcium have been adequately reviewed by many authors (6, 8) and no further attempt a t review is made here. Previous work has indicated that the agreement of the results obtained by the various procedures is often largely through a compensation of errors and that changes in the concentration of any one of the constituents of a mixture of alkaline earths may affect the separation of the others. This investigation was originated because of the great variation between the chemical and spectrochemical analysis when both synthetic and chemically analyzed standards are used as spectrochemical standards. Material balance studies made with the aid of spectrochemical analyses offer a method for determining the merits of a gravimetric procedure. It is possible to determine the amount of coprecipitation and the losses due to solubility. The effectiveness of different precipitating agents and variations in procedure may be studied and evaluated. The material balance values represent a correction of the gravimetric results for inherent errors. EXPERIMENTAL
Table I.
Reagent Purity Determinations as Per Cent of Reagent Anion
Reagent CaCOa (special) BaCOs (purified) BaCOa (impure) SrCOs (anal.) Ba(NOa)p (anal.) Sr(NOa)z (anal.) SrSOd (purified) BaCrOI (purified) Blank (solids)a a Blank determination of amounts usrd.
Ba
