ANALYTICAL EDITION
November 15, 1942 (3)
Elliott, Sklar. and Acree, J . Research Natl. Bur. Standards, 26, 117 (1941).
(4) Evelyn, Malloy, and Rosen, J . Biol. Chem., 126, 645 (1938). (5) Fujita and Iwatake, Biochem. Z.,227, 295 (1935). (6) Harris and Ray, Biochem. J . , 27, 580 (1933). (7) Kirk and Tressler, Food Research, 6, 395 (1941). (8) Kirkpatrick, H. F., J . SOC.Chem. Ind., 60, 226 (1941). (9) Kreuther and Roe, Proc. SOC.Ezptl. Biol. Med., 47, 487 (June, 1941). (10) Loeffler, H. J., IND.ENG.CHEM.,33, 1308 (1941). (11) Lyman, Schultae, and King, J . Biol. Chem., 118, 757 (1937).
849
(12) McHenry, E. W., and Graham, M., Biochem. J., 29, 2013 (1935). (13) Mack and Tressler, J . Biol. Chem., 118, 735 (1937). (14) Mapson, L., Chemistry & Industry, 60, 802 (1941). (15) Mindlin and Butler, J . Biol. Chem., 122, 673 (1937-38). (16) hforell, S., IND.ENG.CHEM.,A N ~ LED., . 13, 793 (1941). (17) Morgan, A. F., Fruit Products J., 21, 75 (1941). (18) Rolf, L. A., J . Agr. Research, 61,381 (1940). (19) Stone, William, Biochem. J., 31, 508 (1937). OUTSIDID Publication No. 3664. Bureau of Agrioultural Chemistry and Engineering, U. S. Department of Agriculture.
Agar-Agar as a Coagulant for Barium Sulfate EDGAR J. BOGAN' AND HARVEY V. RZOYER The Ohio State University, Columbus, Ohio
T
HE precipitate of barium sulfate in the determination
of sulfate usually consists of very fine particles. Standard procedures recommend digestion for several hours and preferably overnight in the hot solution before filtration. Numerous methods have been proposed to improve the character of the precipitate.
Lindsly (6) proposed the addition of a saturated solution of picric acid as a means of increasing crystal size. Krak (6) recommended digestion in an ammonium acetate solution after decanting the mother liquor through the filter. Ziegeler (8) suggested coagulation of the barium sulfate by precipitating silver chloride in the suspension and subsequent removal of the silver chloride with concentrated ammonium hydroxide. Orlow (7) precipitated a known amount of aluminum hydroxide with the barium sulfate and made a correction for the weight of aluminum oxide in the ignited precipitate. None of these methods has proved entirely satisfactory. Caldwell and Moyer (3) roposed the use of the sensitization enomenon as a means oPcoa ulating analytical precipitates. !key showed that finely divide$ zinc sulfide can be coagulated by the addition of minute quantities of gelatin.
It has been found t h a t positively charged barium sulfate which is obtained when sulfate is precipitated by an excess of barium ions can be coagulated by the addition of a trace of 1 Present address, Department of Chemistry, University of Maine, Orono, Maine.
I .i\
5>
-
'1
-/D
u 0S.C w 'a -t Io:
-05
'
t
+Lo
- 05
0
65-
0
/o-
O
0
.
FIQURE2.
0
'
0
O
0
0 0
0
0
o
o
o
o
o
0
m
O
0
'
10
MOBILITY OF PARTICLES OF BAF~IUM SULFATE IN ABRAMSON ELECTROPHORESIS CELL Measurementa on same eolutions as in Figure 1
agar-agar. Approximately 1 mg. of agar-agar will cause the flocculation of a n ordinary analytical precipitate of barium sulfate obtained in the determination of sulfate. On the other hand, negatively charged barium sulfate obtained in the determination of barium is not appreciably improved by the addition of agar-agar. However, this precipitate, as a rule, causes little difficulty in filtration. Another troublesome property of finely divided barium sulfate is its tendency to creep u p t h e sides of t h e funnel or filtering crucible. Creeping seems to be completely eliminated from precipitates coagulated with agar-agar,
Procedure
1
5 0
0
c w 2
6
ul
o
O
0
0
o
o
o
o
c
I
O
0
0
:FIGERE1. EFFECTOF AGAR-AGARON TIMEOF SETTLISG OF PRECIPITATES OF BARIUM SULFATE Each point represents separate sample
The sulfate is reci itated as usual in a hot solution containing 1 ml. of 1 N hygochiric acid by the slow addition of 5 per cent barium chloride solution. After precipitation, from 0.5 to 1 ml. of a solution of agar-agar containing 1 mg. per ml. is added a drop a t a time. After each drop the suspension is stirred rapidly for about 10 seconds. Some coagulation can be observed after the introduction of the first drop; however, the best coagulation usually appears after the addition of about 10 drops of the coagulating agent. The optimum amount of the agar-agar solution is indicated by the flocculation and rapid settling of the precipitate. After settling, the precipitate somewhat resembles coagulated silver chloride. A study was made of the effects of adding agar-agar to precipitstes of barium sulfate in order to determine the limit-
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
850
Vol. 14. No. 11
Figure 3 shows the results of a series of measurements on a single suspension. The beginning of peptization is indicated by the rapid increase in the time required for 40 mg. of pre12; 0 35MG Bas04 cipitate to settle after the addition of 1.6 mg. of agar-agar. The time required for 40 mg. of barium sulfate to settle withlot out the addition of the coagulating agent was so long that i t was impracticable to measure it. Several series of analyses were made to determine the effect of the addition of agar-agar on the digestion period and on the accuracy of the method. Five determinations were made without agar-agar in which the precipitates were digested overnight on the steam plate. An average weight of 0.1009 gram of barium sulfate was obtained from 25 ml. of the stock sodium sulfate solution with an average deviation of 0.00018 gram. In ten determinations, agar-agar varying I in quantity from 1.2 to 2.0 mg. was added to each one and 00 02 04 06 filtration was accomplished within 30 minutes after precipiMG. AEAR-ZAGPI~ tation. An average of 0.1008 gram of barium sulfate was FIGURE 3. TINEOF UETTLING OF SINGLESUSPENSION OF BARIUM obtained from 25 ml. of the sodium sulfate solution with an SULFATE average deviation of 0.00016 gram. All the determinations Increased amounts of agar-agar added indicated that coagulation of the precipitate and 30 minutes digestion gave results equal in accuracy to those obtained without coagulation after overnight digestion. However, ing quantities of agar-agar within which optimum coagulation the addition of agar-agar did not eliminate high results when occurs, the minimum quantity for peptization, and the efbarium sulfate was precipitated in the presence of approxifect on the accuracy of the determination. The effect of the mately 1 per cent potassium nitrate. No detectable reduction agar-agar on the electric charge on the particle was also obof the sulfate mas indicated when the precipitate was served by measuring the mobility of the particle in an Abrammoistened and tested with a drop of phenolphthalein after son electrophoresis cell. ignition of the barium sulfate which had been coagulated with agar-agar. Reagents and Solutions The applicability of the procedure to a n actual sulfate AGAR-AGAR SOLGTION.Agar-agar, U. S.P., ash 4.2 per cent, determination in which difficulty is frequently encountered was used without further purification. A solution containing 1 mg. per ml. was prepared by suspending 0.5 gram of agar-agar was tested in a number of coal analyses. The samples of in 50 ml. of cold water and adding this to 450 ml. of near boilin coal were analyzed according to the Eschka method as given water. The solution was then stirred constantly as it was heate2 by Griffin (4). The agar-agar was added dropwise to the hot to boiling. Such a solution will retain its effectiveness for several solution directly after precipitation of the barium sulfate and weeks. BARIUMCHLORIDE SOLUTIOS. A 5 per cent solution of barium the solution was filtered immediately without digestion. An chloride dihydrate was prepared. average of 1.46 per cent sulfur was found with deviations of SODIUM SULFATE SOLUTION.A sodium sulfate solution of such *0.01 per cent in seven determinations. Another analyst strength was prepared that 25 ml. of the solution gave approxifound 1.50 per cent sulfur b y standard procedure without mately 0.1 gram of barium sulfate. agar-agar with overnight digestion. I n these samples, 10 Experimental drops of the above agar-agar solution produced excellent coagulation. The coagulation of the barium sulfate was measured in an apparatus similar to that used by Calbeck and Harner (3)in Discussion sedimentation measurements. A glass cylinder containing the suspension of barium sulfate was supported over the pan of an Since the optimum concentration of a sensitizing agent analytical balance. A watch glass with a small glass rod through varies with the ionic strength of the solution, the most efits center was placed in the cylinder and the rod was hooked to the arm of the balance. The rate of settling of the barium sulfate fective quantity of agar-agar will differ slightly in different was measured by noting the time required for a iven undersolutions. Figure 3 shows, however, that the limits are not water weight of barium sulfate to settle on the watcl glass. All so critical as to cause difficulty in practical analysis. Slightly precipitations were made in the cylinder from 230 ml. of solution less agar-agar is required if it is added dropwise than if i t is containing 25 ml. of the sodium sulfate solution and 1 ml. of N hydrochloric acid. The solution was stirred with an electric added all a t once. stirrer while 20 ml. of the barium chloride solution were added The measurements of the electrophoretic mobility of the at a constant rate from a buret equipped with a capillary tip. particles show that peptization begins without appreciable When precipitation was complete the cylinder wm placed over change in the negative charge on the particle. The observathe pan of the balance and the suspension was stirred by pulling the watch glass up and down 20 times in the solution. The tions also show that less than 0.1 mg. of agar-agar reverses watch glass was then hooked to the balance and the time rethe charge on the particles of barium sulfate. quired for 35 mg. of barium sulfate to settle on the watch glass was measured with a stop watch. Each solution was then treated with agar-agar solution and stirred 20 times with the watch glass, Literature Cited and the time-weight measurements were repeated. o
40MG Bas04
ZF
Observations were thus made on the effect of adding increased amounts of agar-agar to separate freshly precipitated suspensions of barium sulfate. The results are shown in Figure 1. After the rate of settling was measured for each precipitate, a portion of the suspension was placed in an Abramson (1) electrophoresis cell and the mobility of the particles was determined (Figure 2). Less than 0.1 mg. of agar-agar reversed the sign of the charge on the particles.
(1) Abramson, H . A., Trans. Faradag SOC.,36, 5 (1940). (2) Calbeck, J. H., and Harner, H. R., IND. ENQ. CHEJI.,19, 58 (1927). (3) Galdwell, J. R., and Moyer, H. V., J. Am. Chem. SOC.,57, 2372 (1935). (4) Griffin, R. C., “Technical Methods of Analysis”, 2nd ed., p. 215, New York, McGraw-Hill Book Co., 1927. (5) Krak, J. B., Chemist-Anal&, 5, 26 (1912). (6) Lindsly, C. H., IND.ENQ.CHEM.,ANAL.ED.,8, 176 (1936). (7) Orlow, I. E., Z. anal. Chem., 98, 326 (1934). ( 8 ) Ziegeler, Pharm. Centralh., 22, 555 (1881).
