V O L U M E 2 8 , N O . 4, A P R I L 1 9 5 6 results. The rilira-calcium carbonate mixtures should be dried at m"C. before weighing for mixing with the germanium and carbon to erpd moisture absorbed during the original mixing ooerations. LITERATURE CITED (1) Fits, E. J., Murray, W. RI.. IND. ENO.CHEM..ANAL.Eo. 17, 145-7 (1945). kling, C . E., Speetrochim. A d a 4 . 4 3 9 - 4 5 (19511. (2) Gamble. L. UT., (3) Hela. A. TV., Seribner. B. F.,J . Research Natl. Bur. Sfandads 38, 4 3 9 4 7 (1947). (4) Herdle. A . J.. Wolthorn, W. J., ANAL.CHEM.21, 705-7 (1949). ( 5 ) Hillebrand, W. F.. Lundell. G. E. F.. "Applied Inorganic Analysis." pp. 698-726, Wiley. New York. 1929. (6) Jaycox. E. K.. J . Opt. SOC.Amer. 37, 162 (1947). (7) Kvalheirn. Aslak, Ibid.. 37, 585 (1947).
473 (8) Oshry. H. I., Bnllsrd, J . W.. Schrenk. H . H., Ibid.. 32, 672-SO (1942).
(9) Pierce,
w,C,, Naehtrieb, N, H,, IND,
ENG, CHEx,, ANAL,
Eo.
13, 774-81 (1941). (10) Smith, R. W., Hosgbin, J . E., J . Am. Carom. Soe. 29. 222-8 (1946). (11) Steinberg. R. H.. Belic, H. J.. ANAL.CHEM.20, 72 (1948). (12) Strock. L. W., Appl. Spectroacopll 7 , 64-71 (1953). (13) Zander. J. AI., Terry. J . H . . J . A n . Ceram. Soc. 30, 366-70 (1947). RBCEWFDfor review A ~ r i l1, 1855. Aocepted Fohroary 6, 1956. Taken in part from the the& mhmitted by John W. Anthony to the Graduate Sohool of Southern Methodist University in partial fulfillment of the requirements for the degree of maater of soienee. A cooperatire proiect between the Department of Chemistry, Southern Methodiat University. Dallas, Ter., and the Magnolia Petroleum Co.. Field Resehroh Laboratories.
Dallaa. Tm.
Effect of Aging Solutions of Barium Chloride on Particle Size of Barium Sulfate EDGAR J. BOGAN' and HARVEY V. MOYER McPherson Chemical Laboratory, The Ohio State University, Columbus 10, Ohio
The aging of barium chloride solutions which were used t o precipitate barium sulfate was found to cause an increase in the particle size of the precipitate. Filtration of a freshly prepared solution of barium chloride through a line sintered-glass or porcelain filtering crucible produced the same effect as aging. The particle size of the precipitate seems to be a function of the number of nuclei which are available as starting points for crystallization. The origin of the nuclei wae not established with certainty, but considerable evidence supports the theory that aggregates of incompletely dissolved barium chloride i n the fresh solutions may 8erw a s nuclei for starting crystals of barium sulfate.
times the diameter of the average crystal. The effect of aging the harium chloride on the size of the barium eulfste rrystals is shown in B, C, D,and E of Figure 1. The effect of filtering a fresh solution of barium chloride through a fine (2- to 5- micron)
S.
TUDIES on the coagulation of barium sulfate ( 5 ) by use of minute quantitiw of agar led to the observation that marked dilkenees in the pnrtirle size of precipitates were caused by the age of the solutions of barium chloride which were used to precipitate barium sulfate. An abstract ( 5 ) of these studies was published in 1949. Similar observations have been reported by Fischer and Rhinehammer (7). The significance of the age of precipitating solutions Seems to have been overlooked by the many investigators (8)who have studied the factors affecting the particle size of analytical precipitates. However, Bancroft ( 1 ) stated that, in his opinion, the nnmher of nuclei present in solution is more important than the extent of sopersaturation &B proposed by von Weimarn (8). Benedetti-Piehler (g)in an exchange of correspondence with one of the authors (4) reported that he found an aging effect which disappeared on recrystallizing the barium chloride. However, he mixed the sulfate and barium solutions simultaneously near boiling temperatures, whereas the authors added the barium chloride solution from a pipet with a constant delivery time a t room temperature. Benedetti-Pichler reported barium Bulfate crystals of 5 to 6 microns from purified barium chloride. This size i s approximstely the same as was obtained in this laboratory from fresh solutions of barium chloride. This is shown in A of Figure 1, in which the scale division of 18 microns is close to 3 I Preaent address. Department of Chemistry, University of Maine, Orono, Maine.
Figure 1.
Crystals of harium sulfate
Cryatalsformed underidenticaloqnditions e x c e ~ tfor treatment of 5% bariumehloride dihydratesolutmns. A . Freah aolution E . Aged 1 week B . Aged 2 hours F . Fresh aolution filtered through C. Aged 7 hours fin? aintered-glass filter D . Aged 24 hours 1 sealediviaion = 0.016 mm.
474
A N A LY TICA L C HE M ISTR Y
Selas filtering crucible is shown in P of Figure 1. Fully aged or filteied barium chloride solutions produced crystals from 7 to 10 times as large as those obtained from fresh barium chloride sohtions. Filtration of barium chloride solutions through Blue Ribbon S. and S. filter paper had practically no effect on the crystal size of the barium sulfate. The effect of aging solutions of barium chloride was observed, for the most part, by measuring the rate of settling of suspensions of barium sulfate. The sedimentation nieasurements were made a t temperatures constant within 1O C. The apparatus used was similar to the one designed by Calbeck and Harner (6) and is shown in Figure 2. The series of curves shown in Figure 3 was obtained by this method. The differences in settling rates after I week are probably not significant, because thcy are close to the precision of the method of measurement.
cI
0 ~
m u)
a
9
15-
IO-
0
20
10
40
30
60
50
80
70
MINUTES
Figurc 3.
Settling rates of barium sulfate from 5 % of barium chloride dihydrate
solutions
EXPERIRIENTAL
Procediire. A solution of sodium sulfate which had been aged for several weeks was used to supply the sulfate ions for the precipitation of barium sulfate. The concentration of the sodium sulfate was adjusted so that 25 ml. gave 0.100 gram of barium sulfate. I n all precipitations 25 ml. of the sodium sulfate solution was delivered from the same pipet into a 300-ml. Erlenmeyer flask, 1 ml. of 1N hydrochloric acid mas added, and then the solution w m diluted with 200 ml. of distilled water. The contents of the flask were mixed thoroughly and permitted t o stand for a fern minutes until the agitation from mixing had subsided. Then 25 ml. of 4 or 5% barium chloride solution was delivered a t room temperature and a t the masimum rate of flow from a pipet which was held vertically approximately 1 inch above the surface of the sulfate solution. The same pipet, ndiich had a delivery time of 35 seconds, was used in all precipitations. After addition of the barium chloride, the contents of the flask were thoroughly shaken and permitted to stand for 24 hours a t room temperature before measuring the settling time of the precipitate. A fern degrees difference in temperature at the time of precipitation was found to cause a negligible difference in the size of the crystals. The rate of settling, however, was sensitive to changes in temperature, hence settling rates m r e considered valid only if the temperature remained constant within 1' C. during the measurement.
h"NU1ES
Figure 4.
ance. The watch glass was then quickly hooked into the stirrup of the balance and the chain was adjusted until a steady settling rate was observed. After a little practice the position of the chain a t the start of the observations could be checked within 5 mg. of the same starting weight. Small additions of weight were made by rolling down the chain as the barium sulfate settled on the watch glass. The chain weight was increased as soon as the pointer was displaced approximately 0.5 division from the
V
The rate of settling of the precipitate was determined by observing, with a stop watch, the time required for 5-mg. increments (under water weight) of barium sulfate to settle on a watch glass attached by a glass rod to the left arm of a damped chainweight balance. At the start of the measurement the precipitate was dispersed by moving the watch glass up and down in the solution with the container in place under the arm of the bal-
Settling rntcs of barium sulfate
From barium chloride dihydrate A . Fresh solution 4% B . Fresh solution'of recrystallized barium chloride
0
I IO
I
I
20
30 '
Figure 5.
I
I
40
50
1
io
-
70
80
MINUTES
Settling rates of barium sulfate
From barium chloride dihydrete A . Fresh solution, 5 % B . Fresh solution filtered t.hrough fine (2- to 5- micron) sinteredglass filter
V O L U M E 28, NO. 4, A P R I L 1 9 5 6
475
central position on the pointer scale. Observations were made to show the settling time for 25 to 35 mg. (under water weight) of barium sulfate. Various factom which niight alter the size of the crystals of barium sulfate mere investigated.
/:: w
Distilled Water. Ordinary distilled water, doubledistilled water from thoroughly steamed apparatus, and water distilled from a solution of barium chloride were used to prepare solutions of barium chloride. Only a slight increase in the particle size of barium sulfate was obcrerved in precipitations made from solutions prepared from highly purified water. However, doubledistilled water was used in all subsequent experiments.
IO
a 4c 45
liecrystallized Barium Chloride. Reagent grade barium chloride was dissolved in hot water and filtered through a fine sintered-glass filtering crucible. The reciystallized barium chloride was used to prepare a solution of barium chloride which was used immediately to precipitate barium sulfate. A slight increase in crystal size was observed as shown in Figure 4, but the increase in particle size was not comparable with that obtained from aged or filtered barium chloride solutions as shown in Figure 5. Concentration of Barium Chloride. The conrentration of barium chloride in the solutions which were allowed t o age was either 40 or 50 grams of barium chloride dihydrate per liter. N o
35 30
CY
"
25
0)
a1
ln
20
2' 57
L
5s
MINUTES
Figure 7. AI. &I.
2. B'I' E::!:
Settling rates of barium sulfate
Fresh 4 % solution of recrystallized barium chIoride dihydrate From solution A after filtering Fresh solution o f anhydrous barium chloride From solution B after filtering From B I I after &ration evaporation and dehydration From solution B ~ I after'aging I 72 ha&&
The large crystals reappeared on filtering through sintered glass, but after a second evaporation and dehydration the fine crystals again formed when a fresh solution was used i o precipitate barium sulfate. These results are shown in Figure 7. Effect of Temperature on Aging. If barium chloride is dissolved in boiling rvater, then allowed to cool to room temperature and used to precipitate barium sulfate, the precipitated particles are larger than crystals obtained from solutions of baiium chloride prepared at room temperature and aged for the same length of time. The effect of temperature on the rate of aging is indirated in Figure 8, which shows that somewhat larger crystals of barium sulfate were obtained from a solution of barium chloride which had been aged for appioximately 6 days a t a temperature about 20" C. higher than a second solution, which was aged in a refrigerator.
I5
J
2 z.
10 5
0
20
10
30
MINUTES
Figure 6.
Settling rates of barium sulfate
r
/
m 0 D
From 1% barium chloride dihydrate
A. B.
Frelrh solution Aged 24 houra C. Fresh solution filtered through fine sintered-glaas filter
m
5 v
2 J
30
20
10 I
difference in the aging properties of the 4 and the 5% solutions was observed. However, when the concentration was reduced to I%, the aging effect appeared complete in 24 hours as shown in Figure 6. Dehydrated Barium Chloride. Much smaller crystals of barium sulfate \?-ere obtained from fresh solutions of the dehydrated salt than from similar solutions of the hydrated salt. Aging the solutions of the dehydrated salt caused the usual increase in the particle size of the barium sulfate. A number of experiments were made to determine whether a filtered solution of barium chloride vhich gave large crystals of barium sulfate would continue to give large crystals if the solution was evaporated to dryness in a platinum dish, dehydrated, and then diseolved to prepare a fresh solution. The formation of even finer crystals of barium sulfate 11-vas observed from such solutions.
I
10
0
Figure 8 .
20 MINUTES
,
30
I
40
Settling rates of barium sulfate
From barium chloride dihydrate
A. B.
Aged G days a t G o C. Aged G days a t room temperature
Powdering the Barium Chloride. A fresh solution of barium chloride was prepared from crystals ground to a fine powder in an agate mortar. Extremely fine crystals of barium sulfate Tvere obtained from the ground hydrated salt. They were similar in size to those obtained from the dehydrated salt. The effect of powdering the barium chloride is shown in Figures 3 and 9.
ANALYTICAL CHEMISTRY
476 Large Crystals of Barium Chloride. Large nearly perfe1:t crystals of barium chloride were prepared by the slow growth of a few crystals suspended for several weeks in a slightly supersaturated solution of barium chloride. A single crystal weighirg 2.720 grams was dissolved in 68 ml. of double-distilled water. A 25-ml. portion of the fresh solution was used t o precipital e barium sulfate in the usual manner. For the first time large crystals of barium sulfate were obtained from a fresh unfiltered solution of barium chloride. The settling rate is shown in Figure 9, curve A . A slight increase in crystal size was observed after aging 48 hours as shown in Figure 9, curve B .
Experiments were made to test vaiious theories regarding the source of the crystal nuclei. Dust particles, traces of barium sulfate, dissolved air, and impurities in the distilled water and the barium chloride were ruled out as accounting for the aging effect. Traces of barium sulfate seemed a possible explanation until it was found that barium chloride in a filtered solution gave large crystals, but would again produce small crystals if evaporated to dryness, redissolved, and used while fresh. This experiment n-as repeated several times with the same solution (Figure 7). It was concluded that traces of barium sulfate must have been removed, if its removal was the cause of the formation of large crystals in the filtered solution. The reappearance of small crystals after each evaporation and preparation of a fresh solution indicates that the nuclei must come from the barium chloride itself and not from traces of barium sulfate. The only unfiltered fresh solutions of barium chloride vhich gave large crystals n-ere obtained from solutions of large single crystals of baiium chloride. Powdering or dehydrating these crystals again produced a fine precipitate of barium sulfate. 15 An explanation which seems consistent with the observed facts, but which admittedly is not proved, is that a fresh unfiltered solution contains aggregates of barium chloride which have not yet dispersed into barium and chloride ions. These aggregates may serve as nuclei for the starting of barium sulfate crystals. The adsorption of air on the surface of fine IO I5 20 25 30 35 40 45 50 0 5 crystals of barium chloride mag' be a factor in causMINUTES ing the residues of crystals to persist as aggregates Figure 9. Settling rates of barium sulfate for a considerable time. The remarkable fact that large crystals of barium chloride gave large crystals A . From fresh solution of large single crystal of barium chloride dihydrate of barium sulfate may be due to the absence of crystal B. From solution A after aging 48 hours C . From fresh solution of crushed large crystals of barium chloride d i w d r a t e residues to serve as nuclei for crvstallization. The D . From fresh solution of dehydrated large crystals of barium chloridt formation of fine crystals of barium sulfate when the large crystals of barium chloride were powdcred or dehydrated is consistent with the theory of crystal residues Several of the large crystals of barium chloride were crushed and m-ould appear to rule out impurities in the salt as an exto a powder in a n agate mortar and used to prepare a solution oi planation of the observed facts. The effect of filtration through barium chloride. The solution of powdered barium chloride sintered glass removes many nuclei, possibly by dispersion of produced fine crystals of barium sulfate as shown in Figure 9, the aggregates rather than by adsorption, because there was no curve C. The dehydrated salt from the large crystals also proindication of saturation of the glass filter after a liter of barium duced small crystals of barium sulfate, Figure 9, curve D. chloride solution had been filtered. Time for Precipitate to Appear. It was observed that a shorter time was required for the beginning of precipitation when a fresh solution was uscd than when an aged solution of barium chloride SUMRIARY \vas used. An average of 0.6 second from the time the fresh solution entered the sulfate solution was required for visible A marked increase in the particle size of crystals of barium precipitation, whereas 11.5 seconds was the average time for sulfate was observed n-hen aged or filtered solutions of barium visible precipitation when an aged solution was used. chloride were used in' precipitations. The particle size was assumed to be caused by the abundance or scarcity of crystal nuclei in the barium chloride solution, DISCUS SIQN Numerous experiments were performed in an attempt to find The abundance or scarcity of nuclei which serve as starting the source of the crystal nuclei. The observed facts suggest, points for crystallization seems to be the most reasonable exbut do not prove, that aggregates of incompletely dissolved baplanation for the observed facts. If many nuclei are present rium chloride may serve as nuclei for the starting of crystals the crystals of barium sulfate will be small, but if relatively few of barium sulfate. nuclei are available the crystals mill grow to a greater size. The fact that large crystals are always obtained after aging or filtering LITERATURE C I T E D the precipitant suggests that attention should be given this point (1) Bancroft, W. D., J . P h y s . Chem. 24, 100 (1920). in preparing solutions for analytical precipitations. (2) Benedetti-Pichler, A. Ai., A N ~ LCHEar. . 27, 1505 (1955). The effect of aging the precipitant on the particle size of precipi(3) Bogan, E. J., abstract of doctoral dissertation, The Ohio State tates was observed in solutions other than barium chloride. University Press, Columbus, Ohio, 1949. Solutions of sodium sulfate showed a similar, although more (4) Bogan, E. J., 1 h . 4 ~ CHEII. . 27, 1506 (1955). (5) Bogan, E. J., IIoyer, H. v., IKD. ESG. CHEiV., ANAL. E D . 14, rapid, aging effect when used in the reverse precipitation of 849 (1942). barium sulfate. The aging of sodium sulfate solutions appeared (6) Calbeck, J. H., Harner, H. R., Ind. E ~ QChem. . 19, 58 (1927). to be complete in 24 hours. Calcium chloride solutions gave (7) Fischer, R. B., Rhinehammer, T. B., ~ ~ N A CHEX. L . 26, 244 (1954). larger crystals of calcium oxalate after 24 hours of aging. Aged (8) Weimsrn, P. P. von, Chem. Revs. 2, 217 (1925). solutions of barium chloride gave larger crystals of barium chromate than fresh solutions. RECEIVED for review August 2 3 , 1955 Accepted January 3, 1956.
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