ANALYTICAL CHEMISTRY
1314 (6) Howk, B. F.,C S. Patent 2,433,318 (December 1947). (9) Joslyn, A . , Comar, C. L., IND.ESG. CHEW, ANAL.ED. 10,
364 (1938). (10) Xaltby, J. G , Primavesi, G. R., Analyst 74, 498 (1949). (11) Mitchell, John. Jr., others, “Organic Analysis,” vol. I, p. 284, Interscience, Sew ’k’ork, 1953. (12) Mitchell, John, Jr., Smith, D. bI., ANAL.CHEM.22, 746 (1950). (131 Roe. H. R., Mitchell. John, Jr., Ibid., 23, 1758 (1961). (11, Smith. D. 11,l\Iitchell, John, Jr., Ibid., 22, 750 (1950).
(15) Snell, F. P., Snell, C. T., “Colorimetric Methods of dnalysis,” 3rd ed.. vol. 111. p. 251, Van Kostrand, Xew York, 1953. (16) Thurston, J. T., Carpenter, E. L., Derbenwick, F., “11anufacture of Acrylonitrile from Satural Gas,” preprint from Fourth World Petroleum Congress, Section IT-c, Rome. Italy, June 1955. RECEIVED for review January 20, 1956. .4ccepted April 6, 1950. Division of Analytical Chemistry. 11th Southwest Regional Meeting, ACS, Houston, Tex., December 1955.
Determination of Particle Size with a Simple Recording Sedimentation Balance J.
G. RABATIN and R.
H. GALE
Advance Development Laboratory, Chemical Products Plant, General Electric
A simple automatic recording sedimentation balance utilizes a sensitive spring to weigh the particles settled on the pan. I s the weight on the pan changes, a shutter mechanism intercepts parallel light reaching a photocell. The resulting change in photocell current is recorded automatically by means of a Speedomax recorder. The sedimentation balance is simple in construction and easy to operate. Its precision is good and results compare favorabl! with those obtained with the Andreasen pipet.
T
HE use of an analytical balance for weighing particles settling out of a suspension was first described by Oden ( 6 ) . This method is generally considered accilrate, but requires constant attention and tedious neighings. A recent modified form ( 2 ) of the sedimentation balance utilizes a torsion wire to weigh the particles settled on the pan, but it also requires periodic maniial recording of the data.
Co., Cleveland, Ohio
The automatic recording sedimentation balance descriliecl utilizes a sensitive spring to weigh the particles settled on the pan. As the weight on the pan changes, a shutter mechanism intercepts parallel light reaching a photocell, and the change in photocell current is recorded automatically by a Speedomax recorder. The instrument is simple in construction and en$>-to operate. PRINCIPLE
The principle of operation may be illustrated by Figure 1
A pan, F , is immersed in a settling vessel, G, which contains a suspension of particles. The pan is attached to the l o w r end of a shutter, D,by means of a stiff Tire. The shutter, in turn, is Light originatattached to the lower end of a sensitive spring, ing at source, 8 . is collimated by lens, B, and is intercepted by the photocell, E . As particles settle on the pan, a dorrnward extensiorl of the spring occurs. ~h~ shutter, Inoving simultaneously with the pan, intercepts part of the light reaching the photocell. The resulting change in photocell current is recorded automaticallv by means of a Speedomax recorder.
c.
It has been determined experimentallj- that the light outpiit n a s uniform and the photocell response was linear over the ares used for the measurements. Thus, the recorded curve is proportional to the extension of the spring. As the extension of thi. spring is proportional to the weight settled on the pan, the recorded data can be converted directly to data on per cent v right settled and, thus, used for particle size analyses. CONSTRUCTION
A diagrammatic sketch of the sedimentation balance is illustrated in Figure 2 . Additional details are shown in Figure 3.
Table I. Figure 1. Illustration of principle of simplified sedimentation balance
Reproducibility of Sedimentation Balance on Duplicate Analyses
Diameter, P
Weight Analysis 1
97.0 87.5
Automatic recording sedimentation balances have been reported (1, 7), and electronic recording analytical balances suitable for conversion to sedimentation balances have been described (3,5 ) . I n general. these instruments require complicated servomechanism balancing circuits, T o prevent excessive oscillations of the balance arms. addit iorial discriminator or damping circuits also must be used.
i8.5
71.0 03.0 55 0 47.0 39.0 33.0 27.5 2.3 0 19.0
Greater t h a n Diameter Analysis 2 97.0 88.0 7 9 . .j 71.5
g?.n
00 0 48.0
41.0 3 4 . .i 29.3 ’24. .i 20.5
V O L U M E 2 8 , N O . 8, A U G U S T 1 9 5 6
1315
The light source, 1, consists of a 6.3-volt lamp operating from a constant voltage transformer housed in the left-hand eompartment, 15. T h e collimating lens, 2, is a double convex lens with a
to prevenr a twisting action f i the swine: a c i t e;t&ds. ~Tci s p r h g is m d e of stainless steel wire; Type 302 0 012 inch in diameter, and has a body of 1.3 inches. The spring is attached to R movable rod, 3, both enclosed in the spring housing, 4, to prevent oscillations of the sarine due to air ourrents. T h e sedimentation pan, 13, is about '5 em. in diameter iand is constructed of
~
~~
~~~~~~~~~~
the diagram. The a m wire is just lone: enoueh to reach the ton
Ah adjustable dit. 7, is located Letween thk shutter and the photocell for the urpose of adjusting the zero and final recorder positions, A mi&meter located at the side f, the slit is partially illuminated by the collimated light. The shadow of the shutter falls on the scale, so that the total downward extension of the spring may be determined by noting the initial and find slit readings. A lens, 8, is provided to spread the light over a greater portion of the photocell, thus improving the linear remanse of the ahotocell. 9 IGE ahotovoltaic oelli. T h e voltaee drop across t6e nhotookll is a d h s t e d bv meansof a resist&e clee.de, 10, locaied in the righthand eompmtment. The light reaching the photocell can be conveniently interrupted by means of the entrance shutter, 16.
A
F i g u r e 3.
'
Simplified recnrding s e d i m e n t a t i o n balance
_-
IO
.so
.,'
4
0
.
F
8I-L
E
4
SEDIMENTATION
OPERATION
Complete dispersion of the suspended particles in a medium is essential for accurate particle size measurements. There is no teohnique applicable to all suspensions and considerable care is generally needed to ensure adequate dispersion. 2
4
8
16
32
D I A M E T E R , Jl
3
Figure 4.. C u m u l a t i v e weight per cent curves for zinc phosphate
4
4
.. g4
5
I
of about 0.6 cm. The pan is immersed in the medium and zttached t o the shutter. The adjustable rod is changed until a recorder reading of about 72 divisions is reached and the slit reads about 0.2 cm. T h e distance from the pan to the meniscus is about 8 ern. T h e initial pan height, slit, and recorder value8 are noted. The pan is removed from the blank and placed in the suspension, which is then allowed to reach bath temperature. Next, the settling vessel is vigorously shaken in a rotating manner while a thumb is placed over the center hole. The jar is quickly placed in osition and the pan wire is attached to the shutter. This s h o d take less than 5 seconds. The entrance shutter is immediately opened and the settling recorded. At the end of the run, the final slit value is recorded. The difference between the initial and final slit readings indicates the distance the pan has settled durine: the m. This value is subseauentlv used in the eaIcdations. After the settling curves are obtained, the weight distribution curves may be calculated rtccording to the procedure of Gaudin, Sehumann, and Schlechter (4). This consists of plotting weight per cent settled, p , against In t (seconds). The curve is differentiated by the method of tangents to give d p / d In i (seconds), which is plotted on the same graph. The difference p - d p / d In 1 (seconds), represents the weight per cent of particles greater than a given diameter.
.
"
I
1
I
Ik
15
F i g u r e 2.
lb16
I
;1 13
I
12 1 2
\
'111 1
I
10
S c h e m a t i c d i a g r a m of simplified sedimentation halance
In this laboratory, the dispersing media generally used are m t e r containing Dsxad 11 as a. dispersing agent, butyl acetate, or methanol. From 1.0 to 1.5 grams of powder are used for an nnalwis, depending On the density of the powder and the semitivity settings of the instrument. After 400 ml. of suspension have been prepared, the instrument is adjusted by use of a blank consisting of 400 ml. of the proper dispersing medium. The exit slit is adjusted to a vertical opening
RESULTS AND DISCUSSION
When the adjustable slit opening is set a t 0.6 ern. and the resistance decade is set a t about 1500 ohms, the sensitivity of the instrument is such that one division on the Speedomax recorder Paper (100 divisions full scale) corresponds to a change of 0.006 cm., which, in turn, represents about 0.0015 gram of phosphor settled on the pan. Increased sensitivity is obtained by reducing
ANALYTICAL CHEMISTRY
1316 the slit opening and using more sensitive springs. As little as 0.3 mg. may be measured. Because of the unusual features present in this sedimentation balance, considerable effort was made to determine the accuracy and reproducibility obtainable. Repeated analyses on the same sample gave similar results. An example is shown in Table I for the particle size analyses of calcium halophosphate dispersed in water.
1001
I
1
I
I
I
SED1MENTATION
ANDREASEN PIPET
I'
I 70
1 1 1 2
4
DIAMETER
8
16
32
,p
Figure 5. Cumulative weight per cent curves for zinc silicate
Good precision is obtained in the size range of 2 to 30 microns. Some hindered fall may occur because of the relatively large sample used (2.5 grams per liter). This disadvantage is balanced by the fact that use of a larger sample minimizes errors due to poor sampling. Procedural errors are present to some extent. During the final dispersing operation, about 5 seconds are required to set the settling vessel into position and to attach the pan to the shutter, and 3 to 5 seconds are required for the pan oscillations to cease. Thus, about 10 seconds elapse before undisturbed settling occurs. During this time some coarse particles will settle out. The error associated with determining percentage of particles larger than 35 microns is considerable, as
these generally settle out in less than 1 minute. This type of error is present in practically all liquid settling methods and can be minimized by increasing the settling height t o 20 cm. or more. The accuracy of the instrument could be evaluated on a comparative basis only, because there are no absolute methods for determining particle size distributions. A comparison with the Andreasen pipet was considered the best approach, as both methods utilize liquid dispersions and weight distributions are obtained Two comparisons are illustrated in Figures 4 and 5. Good agreement n-as found between the two methods, furthcr indicating that the basic principle of the simplified sedimentation balance is sound and that other possible sources of error, such as the small downward displacement of the pan, are not significant. An inherent source of error in the Oden method of analyzing the experimental curves is in the need for differentiation of the curve. However, because good agreement was obtained with the Andreasen pipet method where no differentiation is employed, it must be concluded that this error is relatively small. Another possible source of error in the sedimentation method is that small convection currents may be caused by changes in suspension density directly under the pan as particles settle out. I n the present work this change in density would be from about 1.0012 to 1,0000 (based on 2 grams of powder per liter of suspension). Thus only small convection currents should occur. Additional evaluations and comparisons are being made with other particle size instruments, such as the Sharples llicromerograph, turbidimeter, and Roller particle analyzer. ACKNOWLEDGMENT
The authors \\-ish to acknowledge the helpful suggestions and criticisms of Shannon Jones and Fred Geraghty. LITERATURE CITED
(1) Bishop, D. L., Bur. Standards J . RePearch 12, 173 (1934). (2) Bostock, W., J . Sci. Instr. 29, 209 (1952). (3) Edwald, P.. IND,ESG. CHEV., ANAL ED. 14, 66 (1942). (4) Gaudin, A. M., Schumann, R., Schlechter. A . W., J.Phys. Chem. 46, 903 (1942). ( 5 ) Lohmann, I. W., Reo. Sci. Zntr. 21, 999 (1950). (6) Oden, S., Soil Sci. 19, 1 (1925). (7) Svedberg, T., Rinde, H., J . Am. Chem. SOC.45, 943 (1923). RECEIVED for review October 3 1 . 1955. Accepted April 19. 1956.
Evaluation of 2-Furoyltrifluoroacetone as an Analytical Reagent RUSSELL T. MclNTYRE, EUGENE W. BERG, and DAN N. CAMPBELL' Coates Chemical Laboratories, Louisiana State University, Baton Rouge, La.
2-Furoyltrifluoroacetone is a sensitive nonspecific spot test reagent suitable for detecting as little as 2 Y of some metals in 0.1 ml. of solution. It may be used to concentrate and isolate heavy metals by precipitation, extraction, or chromatography of the metal chelate. Light absorption characteristics of the metal chelates in organic solvents suggest application of the reagent to the spectrophotometric or fluorophotometric determination of some metals. As a precipitant for the gravimetric determination of palladium, 2-furoyltrifluoroacetone compares favorably with dimethylglyoxime.
S
EF'ERAL p-diketones have been studied in this laboratory
to determine their potential use as analytical reagents. This study concerns the analytical applications of 2-furoyltrifl uoroace tone. Probably the most interesting characteristic of the p-diketone is its ability to form stable chelates with a large number of simple metal ions. Many of these metal chelates are easily prepared, stable, intensely colored or fluorescent, insoluble in water, and soluble in common organic solvents. The analytical applications suggested for this reagent are based on the inherent characteristics of the metal chelates. 1
Present address, hIonsanto Chemical Co., Texas City, Tex.
