Determination of Strontium in the Presence of Calcium PAUL B. STEWART AND KENNETH A. KOBE', University of Washington, Seattle, Wash.
I
N CONNECTIOX with a phase rule study of the ternary
to make this solution a good solvent. Results of this work are shown in Table I and Figure 1. Among the variations in procedure tried were varying the length of time with a single extraction, repeated extractions of differing times, ratio of acetone to total salts, and finally a continuous extraction process using Jena sintered-glass filter crucibles in a modified Soxhlet apparatus. None of these gave satisfactory results.
system calcium nitratestrontium nitrate-water in process in this laboratory an accurate method for the determination of strontium in the presence of calcium was needed. As the system is being studied TTith the idea that the data gathered may be used as the basis for a fractional crystallization process for preparing pure strontium nitrate from impure or low-grade strontium ores, it was further desired that the analytical procedure be capable of use as a technical method.
TABLEI. SOLUTION OF CALCIUM NITRATE LVD STRONTIUM NITRATEIN ACETONE AT ROOMTEMPERATURE Ca(N0a)z Time elapsed, Salt, gram per minutes ml. of soln.
Sr(N0a)r Time elapsed, Salt, gram per minutes ml. of soln.
The classical method for the determination of strontium in the presence of calcium is by the extraction of the calcium nitrate from the mixed alkaline earth nitrates with a mixture of absolute alcohol and absolute ether (1). These solvents are both expensive and hygroscopic, this latter feature being especially important in many localities. The acetone extraction method of Shreve and co-workers (2) seemed to obviate some of these undesirable features. The results claimed for it were substantiated by trial, but only in mixtures containing a calcium to strontium ratio of 3 to 1 or richer in strontium. With increasing proportion of calcium to strontium in the mixture of the salts the method becomes less and less reliable.
v -
0
/O
20
40
30
Per Cent Srh'oJ2 Presem
FIGURE 2
It was then decided to standardize a procedure, and to obtain a calibration curve for this method. The variables which it was deemed necessary to control were ratio of solvent to total salts, time of extraction, and manner of extraction. Accordingly, the following procedure was adopted and rigidly followed : For the analysis of a sample containing other substances than calcium and strontium nitrates it is necessary to isolate these alkaline earth nitrates as in the gravimetric analysis for calcium in limestone. Briefly, this consists of putting the sample in solu-
80
40 E/upsed
Time- Mibutes
/zo
-
TABLE 11. %
4.42
FIGURE 1
Trial
As acetone is both cheap and ordinarily readily available, it was decided to attempt to modify the acetone extraction
1 2 3 4 5 6 7 8 9
method so that sufficiently accurate results could be obtained. Accordingly, the work of Williams and Briscoe (5) was repeated in part, and their finding that calcium nitrate is extremely soluble and strontium nitrate essentially insoluble in acetone a t room temperature was confirmed. It was also found that the rate of solution of calcium nitrate in an acetone solution of calcium nitrate was too slow a t the end of an hour 1
CALIBRATION OF
7
Present address, University of Texas, Austin, Texas.
298
%
%
13.24 20.59
%
%
33.30 48.84 c Strontium Nitrate Found % % % % % % 5.00 10.90 14.92 22.52 34.95 49.95 5.45 9.100 14.67 24.404 36.850 50.45 5.34 10.70 15.22 21.85 34.90 50.70 4.46 11.20 14.47 23.75 35.50 50.15 3.895 11.10 15.41 23.05 34.75 50.40 4.92 11.50 5.32 11.60 5.45 10.90 4.98 10.50 5.12 11.05 14.94 22.79 35.02 50.35
Av. Av. deviation 0.70 0
%
9.36
ANALYTICAL PROCEDURE
Strontium Nitrate Present
%
%
% 66.55 66.73 66.45 66.25 66.65
% 85.10 85.20 85.10 83.100 85.30
-
65.55 85.101
..................... .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .....................
1.69
Not used in average.
1.70
2.20
2.72
1.51
66.53 85.20 0.95
0.10
299
ANALYTICAL EDITION
April 15, 1942
di?h are stirred every 8 to 10 minutes, the dish being covered w t h a watch glass a t all other times. At the end of exactly one hour the residue in the dish is filtered off in a No. 3 Jena sinteredglass filter crucible, dried a t 140°,and weighed.
FIGURE 3
tion with hydrochloric acid, after fusing i t with sodium carbonate if necessary. The silica is then removed by re eated dehydrations and filtered off, followed by the removal opiron and aluminum as hydroxides by precipitation with ammonium hydroxide. The alkaline earth metals are then precipitated as carbonates with ammonium carbonate and filtered off from the solution. Treatment of the carbonates.with nitric acid will then yield the desired solution of the alkaline earth nitrates. This procedure makes no provision for separating barium from strontium and calcium. The solution, of sufficient size to yield about 1 gram of anhydrous salts, containing the mixed calcium and strontium nitrates, is evaporated on a steam plate for from 12 to 24 hours, and finally dried in an oven at 140” C. for 24 hours. Drying at a lower temperature was found to be too slow, and tests showed no detectable decomposition of the strontium nitrate at this temperature and for this time. Both the evaporation and drying were generally carried out in 40 X 25 mm. weighing bottles with the covers held slightly open for the escape of vapor by a Ushaped wire clip on the top of the bottle. The mixed anhydrous nitrates are then cooled in a desiccator over phosphorus pentoxide (calcium nitrate is an excellent desiccant itself), and weighed. They are then extracted with c . P. acetone, using 4 ml. of acetone per 100 mg. of salts. The salts are transferred to an evaporating dish for the extraction with the extractant acetone, and thoroughly pulverized with a stirring rod, the end of which has been enlarged. During the extraction the contents of the
Solutions containing known amounts of both alkaline earth nitrates were then prepared, and the foregoing procedure was applied to them. The data in Table I1 were obtained. These are shown graphically in Figure 2, which shows the values obtained by this analytical procedure compared with the true values. The maximum deviation is in the range of 10 to 60 per cent strontium nitrate. In Figure 3 is plotted the deviation in per cent against the per cent strontium nitrate found in the sample by this analytical method. The deviation is subtracted from the per cent strontium nitrate determined t o give the true value. Although a sample yielding about 1 gram of mixed alkaline earth nitrates was preferred, samples as small as 0.40 gram and up to 3 grams were run by this method. The strontium content of these samples ran from a minimum of 4 to 5 mg. up to practically the entire weight of the sample. I n running triplicate samples, almost invariably a pair of values would check to within 5 parts in 1000, based on the original weight of the nitrates. This method has been used on all the analytical Fork on the phase rule study referred to earlier, and the results have been most satisfactory in that they are thoroughly consistent among themselves.
Literature Cited W.W., “Standard Methods of Clieniical Analysis”, 5th ed., Vol. 1, p. 901, Ken, York, D. Van Nostrand Co., 1939. (2) Shreve, R. K.,V a t k i n s , C. H., and Browning, J. C., IND.ENG. CHEM.,ANLL.ED.,11,215 (1939). (3) Williams, P. E., and Rriscoe, H. T. Chern. S e w s , 145, 177 (1932). (1) Scott,
Analysis of the Ternary System EthanolMethanol-Water JOHN GRISWOLD AND J. A. DINWIDDIEI, University of Texas, Austin, Texas
A rapid and accurate physical method of analysis is presented for the ternary system ethanol-methanol-water, which requires the boiling point, refractive index, and specific gravity of the sample. The composition is then read directly from a chart. No assumptions are involved and no adjustment to a definite water concentration is needed.
T
HIS ternary system is encountered in some antifreeze
solutions and certain denatured alcohol formulas and pharmaceutical preparations, although the analysis was developed for use in a study of liquid-vapor equilibrium which will be published later. Early methods of analysis applied t o this system had as their chief purpose the determination of small amounts of methanol in ethyl alcohol and water. Chemical methods of 1
Present address, Humble Oil Bi Refining Co., Baytown, Texas.
analysis were to oxidize the methanol or subject i t t o some other chemical reaction, then determine the compound formed. Leach and Lythgoe ( 3 ) developed a purely.physica1 analysis for the ternary system, using the specific gravity and refractive index. The method embodied two approximations: that the concentration of total alcohol is a function of gravity only, and that the refractive index is linear with the ratio of the two alcohols. The method is necessarily inexact, and has the disadvantage that the rather inaccessible and not highly accurate Hehner alcohol tables must be used to avoid serious errors. Lan e and Reif (9)obtained better accuracy with a similar metho!, by adjusting the alcohol concentration to 50 per cent by volume, then determinin gravity and refractive index. Williams (6) reviewef Leach and Lythgoe’s method, and improved upon it by adjusting the sample concentration to 20 er cent by weight of total alcohol before making final gravity a n f refractometer determinations. Mortimer (6) developed a ternary chart for alcohol concentrations up to 40 per cent by weight in terms of Zeiss refractometer readings, with which the proportion of the two alcohols may beresolved. hlacoun (4) improved Lange and Reif’s method somewhat by adjusting the sample to a concentration of 40 per cent alcohol by weight. The weight per cent is independent of temperature whereas the volume per cent (used by Lange and Reif) is not. Macoun also prepared a table of alcohol concentration in terms of refractometer readings for values between 39.5 and 40.5 weight per cents of alcohol, and temperatures from 15.6” to
