Refractometric Adsorption Analyses Use of Automatic Recording Diferential Refractometer R . A . GLENN, JOY S. WOLFARTH’, AND C. W. DEW.4LT, J R . ~ Coal Research Laboratory, Carnegie Znstitute of Technology, Pittsburgh, Pa. where
The battery-operated continuous automatic recording differential refractometer of Zaukelies and Frost has been adapted to 115-volt alternating current operation and investigated as a tool for following the progrms of liquid chromatographs of colorless materials according to a technique described by Claesson. Integration of the area under the curve in a refractogram obtained through use of the automatic recording refractometer permits quantitative estimation of the individual components in thepercolate from an adsorption column by utilizing the additive property of refractive index. Quantitative refractometric adsorption analyses according to this technique are reported for the first time. Data are given on anaIyses of methylcyclohexane-toluenemixtures on silica gel and examples are presented of the use of the refractometer in the chromatography of coal hydrogenation products.
P
= volume of solute in milliliters V = volume of solution in milliliters ne = refractive index of solution n-2 = refractive index of pure solute nl = refractive index of pure solvent 8 1
Therefore, during chromatographic adsorption analyses, the difference b e h e e n the refractive index of the developer entering the top of the column and that of the percolate leaving the bottom is a measure of the concentration in the percolate of the material heing eluted from the chromatographic column. Furthermore, when only one component of known refractive index i R heing eluted a t a time, the amount, a, of that componcnt bring (,luted may be determined by integration of the concentration, c, of the component as indicated by refractive index over the volume, v , of percolate collected according to equation of Claesson ( 1 , s )
ERIODIC analysis of the effluent from chromatographic columns by chemical or physical methods is an indispensable aid for determining the progress of the liquid chromatography of colorless nonfluorescing compounds. One of the more widely used physical methods is that of refractometry, which was introduced by Tiselius and Claesson (11). Later it was developed in greater detail by Claesson (1, 2 ) , who described three quantitative procedures for its use which he termed displacement development, elution analysis, and frontal analysis. Displacement development has been used widely in the analysis and separation of products from petroleum ( 8 ) , shale oil ( 3 ) ,and synthol (9). On the other Rand, frontal analysis ( 4 , 5 ) and elution analysis have seen only limited use. Since Clwson’s investigation of frontal analysis, several automatic recording refractometers have been reported in the literature ( 6 , 7, fa, lb), but the use of only two has been described (4,5 ) . This paper describes the battery-operated automatic recording differential refractometer of Zaukelies and Frost (12) as modified for 115-volt alternating current line operation and used a t the Coal Research Laboratory in the quantitative analysis of methylcyclohexane-toluene mixturcs by a semimicrotechnique designated ~ L I“refractometric adsorption analysis” and t o check the progress of elution during the chromatographic analysis of. complex mixtures of hydrocarbons obtained from coal by hydrogenation. This new tool has been s h o m to be of practical value in instantaneously following changes i n the concentration of liquids, especially during adsorption analyses of colorless mixtures. THEORY
In dilub aolutions, refractive index is an additive property and for binary systems it may be used as a m w r e of their composition. Thus, the volume of a given solute present in a dilute solution in z given solvent may be calculated from the equation
1
2
Present address, Kopper.8 Co , Verona, Pa. Preswtsddress, MellonInri t.ite, Pittsburgh Pa.
The theory and design of the differential refractometer have been described by Zaukelies and Frost ( 1 2 ) . APPARATUS AND TECHNIQUE
Refractometer. The automatic Continuous recording refractometer employed was essentially the battery-operated instrument of Zaukelies and Frost adapted for 115-volt alternating current line operation (see Figure 1). The A and B batteries used by Zaukelies and Frost have been eliminated. A 115-volt alternating current line-operated power pack regulates both late and filament voltages in the amplifier (Figure 2). In the $ate supply an OD3/VR150J T5,is used to stabilize the input voltage to a second stage of stabilization which employs a VR75, 2‘6. The resulting 75-volt1 doubly regulated supply to the plates is practically independent of line voltage fluctuations over a wide range. An Amperite 6-4 ballast tube, ’7’4, regulates the filament supply. The excellent stability of the power supply is shown by the absence of fluctuations and drift in the record obtained with the lamp off and the sensitivity control, P2, set a t maximum (Figure 3, a). Because any drift in the amplifier with the lamp o f fhas been shown to result from changes in room temperature, all resistors and control potentiometers should have as low temperature coefficients as possible. The lamp a 30-candlepower automobile spotlight bulb with polished surjace, is regulated by a constant voltage transformer. Operation of the lamp by means of a stepdown transformer a t about 5.8 volts instead of the rated 6 t o 8 volts results in a longer life. The stability of the intensity of the lamp when alternating current-operated as shown in Figure 3, b and c, compares favorably with that reported by Zaukelies and Frost for the batteryoperated instrument (12). Four changes have been nude in the circuit of the amplifier (Figure 2) in the interest of increased stability: The plate supply voltage has been decreased to 75 volts, R1 and R2 have been reduced to 22 megohms each, the range of P1 has been decreased from 50,000 to 10,000 ohms, and C2, R8, and R9 have been added. Careful shielding of the phototube, T 2 , was found to be important; consequently, the phototube was dismounted from the Bakelite base and mounted, together with the adjacent circuit elements including the two miniature 45-voIt batteries, on the movable, micrometer-driven base. The entire assembly waa then checked for zero “dark current” output signal and placed in a separate shield. The Brown Electronik recorder used is a conventional 27-mv.
1138
V O L U M E 24, NO. 7, J U L Y 1 9 5 2
1139 An
Y
~
1-
(3)
rtsn a
where
0.W1 inch = displacement of phototube 8 inches = distance from refractometer cell to phototube a = 45" = angle ol incidence of light at diagonal boundary =
7 =
Figure 1.
This value of 1.24 X 1O-O for the change in refractive index which shifts the spot of light on the phototube 0.001 inch is the optical sensitivity of the refractometer and is termed a "refractomil." The "refractornil" may be termed an instrument oonstant, ita value depends solely upon the geometry of the instrument. Whenever changes in refractive index greater than full scalcof thereeordcrilreencountered, the Automatic Recording Differential Refractometer recorder may be readily maintained on scale by shifting the phototube 1 or more mils by means of the micrometer. This technique increases the range of the instrument to rt.0.02 refractive index unit, Any given position of the phototube is accur&tdy reproduecd by attaching to the micrometer handle a. conventional 4-inch radio panel dial with 200 subdivisions per 360"and by always approaching a given setting of the miorometor from the same direction to counteract the slack in the micrometer screw threads.
Table I. Data for Determination of Instrument Constant An"D"C.
0
B1. 9Ovolts
C1 C2. 0.1 mfd. 63: C4. 8 mfd.
F1. 1 hm~..250 volts PI. i o o n n ~ h ~ P2. 2ObOohms R l R2. 22 megohm R3: 20.000 ohma R4, R7. 39 000 ohms R5. 10,000'ohme RB. 5000 ohms RE. 390 000 o h m RQ. icn:ooo ohms
A Mils
An/Mil
Experiment 1 0,00333 27.0 1 . 2 3 X IO-, Expsriment 2 0.01065 85.6 1.24 X 10-4 Average of five determinations on Abbe refractometer.
R10, R11. 5100 ohm R I ~ .9000 ohms. R13. 510 000 o h m R14. 100'ohma 51. Filament supply sz. Piate SUPPiY T I . 6F8G T 2 . 820 T 3 . 6W4 T4. 6-4 (&mpezite) T5. OD%/VR15O TB. OA3/VR75
full scale singlepoint instrument designed to record oontinuously temperatures from 0' to 500' C . using m iron-constantan thermocouple. The normal speed of the chart is 3 inches er hour and the ruling is 20 divisions t o the inch each way, such &at there are 200 divisions acrms the scale and 60 divisionsper hour linearly. The optical sensitivity of the refractometer was determined by introducing aqueous ethanol 60lUtiOns of known refractive index in the ssmole cell and observine: the distance the light 6 D O t was moved wiih the sensitivity control, P2, a t &ut 50% of maximum (Table I). This was accomplished by using the micrometer drive to keep the phototube near the center of the lieht 8DOt 84 indicated bv the recorder. Average8 of remated &ting$ of the phototube which were 0,001 inch t o th6 right and left of the approximate center of the light Bpot were taken in much the same manner a8 "swings" are taken on au anttlvticd balrance and distances less than 1 mil oalculated by jnte olation of the recorder chart. The observed optical fiensitivlty $1.24 X A n for a 0,001 inch movement of the phototube agrees well with the value of 1.25 X as predicted from the geometrical design of the apparstus according to Equation 9:
et
45
Figure3.
90 135 TIME, minute8
180
m
I
Refract0 meter Stability R ecord a t Various Sensitivities
The over-all sensitivity, D, of the instrument, on the other hand, is dependent upon the intenshy of the light, the dwign of the amplifier circuit, the millivolt range of the Brown recorder, and the setting of the sensitivity control, P2,the latter being the only free variable subject to change a t will by the operator. The recorder sensitivity, S-Le., the number of chart divisions, d, equivalent to 1 refractomil, M , or 1 mil (0.M)l inch) movement of the p h o t o t u b e i s determined experimentally by repeated movements of the phototube in 1OT more mil increments with the same liquid in both cells of the refractometer or with no flow
1140
ANALYTICAL CHEMISTRY
through either cell and observing the number of chart divisions the recorder is shifted (see Figure 7 ) . The over-all sensitivity then is calculated according to the equation:
CONSTANT LEVEL RESERVOIR OF DEVELOPER
where
D = over-all sensitivity expressed as An per chart division, d A I = refractomil or optical sensitivity expressed as An per 1 mil movement of phototube; for this instrument, M = 1.24 x 10-4 ~n S = recorder sensitivity expressed as chart divisions equivalent to 1 refractomil-i.e., 1-mil movement of phototube
TWIN PHOTO CELLS L
160
-
140
-
120
Figure 5 .
the amplifier is about 1 hour, while that of the lamp is several hours. Variations in room temperature are reflected in the record because of the changes in the lamp position which result from the uneven thermal expansion or contraction in the lamp supports. Consequently, the most useful over-all sensitivity is about 1 X An full scale. Apparatus Assembly. ; iechematic diagram of the apparatus assembly is shown in Figure 5.
-
3 0 -
ul
z -
0
II a
P-
t-
3 E60
-
40-
L 9 . 4
OO
Apparatus .4ssembIy for Refractometric Adsorption -4nalysis
'
I
20
'
'
40
'
'
60
'
'
BO
TIME, minutes
Figure 4. Operational Record of Refractometer at Different Sensitivities and Uniform Displacements (0.002 Inch) of Phototube
With the sensitivity control P2 and the lamp voltage both set a t maximum, the over-all sensitivity, D , for any position of the zero adjust control is approximately 1.7 x 10-6 An per chart division or 3.7 X 10-4 An full scale or 220 divisions. This full scale sensitivity can be reduced to a practical minimum of about 1 X 10-6 An per chart division or 2.2 X 10-3 An full scale. As in other such instruments (IO, 12), the maximum useful sensitivity of the instrument is limited by the mechanical stability of the light source. Greater sensitivity could be readily achieved if desired by increasing the angle of the diagonal boundary of the refractometer cell and by using an illuminated slit as the light source. Although the instrument is constructed on an &inch channel beam mounted on rubber, the random fluctuations in the An a t 50% sensitivity record are equivalent to about 5 X and vary from day t o day, depending appaiently upon prevailing weather conditions (cf. Figures 3 and 4). The warm-up time of
The outlet tube of a chromatographic adsorption tube (12 mm. in outside diameter X 31 cm.) was connected by means of a stopcock and Tygon tubing t o one side of the split refractometer cell; t o the other side, the reference side, a reservoir of reference solvent was connected. The adsorption column was also provided with a constant-level reservoir of developing solvent. Both halves of the refractometer cell were held a t the same temperature by circulation of water through both sides of the refractometer cell. Technique. The adsorption column used in each experiment was prepared by slow continuous addition of 4.0 grams of prewetted but free-flowing silica gel to the chromatographic tube partially filled with developer, the upper level of which was constantly agitated. Prior to its being used, the column was flushed with fresh developer until the refractive index of the effluent from the column was the same as that of the developer being added a t the top. The sample for refractometric adsorption analysis was then introduced a t the top of the chromatographic column, and the adsorbent kept covered with solution a t all times. After the sample had been added, the addition of fresh developer from the reservoir was continued, the flow regulated to some constant rate by means of the stopcock, a constant flow of reference solvent maintained through the reference cell, and the refractive index of the effluent from the column recorded. This sequence of operations resulted in the production of a refractogram, the shape of which was dependent u n the composition of the sample. M a t e r i a l s . S i E a gel, Davison's aOO-mesh, Code 11. Iso-octane, Phillip's Spectrograde or pure grade. Toluene, Eastman Kodak's No. 325-x (from sulfonic acid). Methylcyclohcxane. Eastman Kodak's KO.P-946 shown t o be toluene-free by ultraviolet analysis. CA LCUL 4TION
The amount of a given component of known refraotive index being eluted singly from a chromatograph column may be calculated by graphical integration of the area under the curve in a refractogram and application of the following equation: (5)
where
A = area under curve in a refractogram expressed in chart squares R = flow rate expressed as chart divisions per milliliter of effluent
1141
V O L U M E 2 4 , NO. 7, J U L Y 1 9 5 2
D = over-all sensitivitj- of refractometer expressed as An per chart division
Q
= quantity of given component eluted expressed in “re-
fractoms”
Table 11. Data from Refractometric Adsorption Analysis over Glass Beads of 1-311. Samples of Iso-octane Containing Methylcyclohexane-Toluene
A “refractom” is the unit of area under the curve of a refractogram corresponding t o a An of 1 X through a volume of 1 nil. The volume, V?,of any given component equivalent t o 1 refractom in a given solvent may be calculated from Equation 1 by substituting 1 x for (n, - nl),1.0 for V, and the appropriate values for the reflactive indices of the pure solute and pure solvent. Then volume T’, of the given component eluted follows from the equation T’,
=
Q X V,
The terms ”refractomil” and “refractom” have been introduced because of their practical value in carrying out refractometric adsorption analyses. The “refractomil” is a unit of change of refractive index; Its magnitude, which is determined solely by the design of the instrument, may vary from instrument t o instrument, especially laboratory models. Its prac,tical value stems from the fact that the phototube is shifted in multiplcs of 1 mil during the recorder sensitivit,y check made before and after each experiment, as \vel1 as during those experiments in which changes in refractive index greater than full scale are measured. The term “refractom” hap both practical and theoretical significance; it may be considered as analogous t o the term “equivalent” in titrimetry. Because it is, by definition, t,hat area under the curve in a refractogram equivalent to a A n of 1 X lo-‘ through a volume of 1 ml. the “refractom” unit has the elements of refractive index times volume. Thus, by use of t,his unit, the “refractom,” it is possible t o make refractometric balances for refractometric adsorption analyses of materials (see Tables I1
Figure 6.
Refractogram of Methylcyclohexane on Glass Beads
. 5 , 53
Solution B
5.68 5 . RR .. d ,93 6.18
5 77 5.51 5.28 A v . 5 . 5 2 I t O . 16
5.83
Av. 5 . 8 4 1 0 17
(6)
DISCUSSION
I
Solution A
Table 111. Data on Refractometric ‘4dsorption Analysis on Silica Gel of 1-RI1. Samples of Iso-octane Containing Methylcyclohexane-Toluene (Solution C) Experiment 1
2 3 4 5
a
Average Found by direct measurement By difference.
MCH. Refractoms
TOL, Refractoms
Total, Refractomi
6 32 6 04 6.67 6.16 6.09
46 4 43.6 42.2 50.2 54.2
52.7 49.7 48.9 56.4 60.3
1 7 . 4 It 4 . 0
53.6 zt 3 . 6
6.25
0.43
3
6 67
54.3
47,6‘L
and 111) regardless of whether or not the individual components are of known refractive index, according t o the equation:
V An = Vi ( A n ) i
+ Vu ( A n ) ? + . . .
,
Vm (An),
(7)
where
L7
of original sample put on the adsorption column An = difference between refractive index of sample and that of pure developer used to make the adsorption analysis VI, Vz,V, = volumes of resultant, chromatograph fractions (An)l, ( A n ) l , (An), = difference between refractive index of resultant chromatograph fractions and that. of developer = volume
The example of an autoniatically recorded adsorptogram, “refract,ogram,” shown in Figure 6, resulted from the development of a 1-ml. sample of a 2.5% solution of methylcyclohexane (LICH) (nL5 1.4208)in iso-octane (nS5 1.3890) over a column of glass beads; it contained 25.0 microliters or 7.95 refractoms of met,hylcyclohexane. At the start iso-octane was flowing through both the reference cell and the sample cell; therefore, a straight line, the “base line,” result’ed, as there was no difference in the refractive index of the liquids in the two cells. When the small amount of the sample solution was introduced into the stream flowing through the sample cell, a change in the refractive index of the liquid in the sample cell resulted and, as shown in the refractogram, the curve shifted away from and returned to the base line as the concentration of the second liquid increased t o a maximum and then diminished t o zero. The integrated area under the curve in Figure 6 represents 8.22 refractoms and a 103.4% recovery, which may be regarded as acceptable in consideration of the probable errors in the volumetric preparation of the sample and in calculating the area under the curve and pipetting the sample. Deviation of the “flowing base line” from the “static base line” (see Figure 7) results from failure of the temperature of the flowing stream to reach that of the prism. If room temperahre is greatly different from that of the circulating water, it may become necessary t o jacket the chromatograph column also. Data from experiments designed to test the validity of Equations 1, 5 , 6, and 7 and t o det,ermine the precision and accuracy of the method are presented in Table 11. I n these experiments
ANALYTICAL CHEMISTRY
1142 the samples under test consisted of iso-octane solutions of methylcyclohexane and toluene in the ratio of 1 to 2. The data obtained on the two solutions by direct measurement of their refractive indices are presented in the second column, and those from refractograms of 1-ml. samples in the third column. The values obtained by these two methods are in good agreement and show a precision of 3 ~ 3 % . METHY LCYCLOHEXANE-TOLUENE MIXTURES
One of the more promising features of this automatic recording refractometer is its use in connection with adsorption analysis of colorless a materials, especially where it is possible to elutp one known component from the column at a time, thus making it possible to estimate quantitatively the amount of material being eluted. If this technique is to be utilized, the developer must not elute any impurities from the adsorbent but 0 must elute the sample completely. .%I1 these conditions are met in the classic separation of aromatFigure 7. ics from saturates using silica gel, and through use of the automatic recording refractometer a method termed "refractometric adsorption analysis" has been applied to the analysis of methylcyrlohexanetoluene mixtures. The refractogram (Figure 7 ) from the adsorption analysis on silica gel of 1 ml. of Solution c (iso-octane containing 50 p l . of toluene and 20 pl. of methylcyclohexane per ml.) shows that the rapid development of the saturated hydrocarbon, methylcyclohexane, into the percolate by displacement occurred before a slower development of the aromatic hydrocarbon, toluene, into the percolate by elution. Complete separation of the two is indicated by the return of the curve to the base line prior to the appearance of toluene in the percolate. As shown in Table 111, from five such refractograms obtained as above, the average recovery of methylcyclohexane was 6.25 refractoms or 94%; the average recovery of toluene was 47.4 refractoms or 99%. By direct measurement during the preparation of the stock solution, the An resulting from the addition of 2% methylcyclohexane to iso-octane was 5.38 refractomils; and for the addition of 5% toluene to this solution was 38.4 refractomils (by difference) since the total An was 43.8 refractomils. Thus, 1 ml. of this solution contained 6.67 refractoms of methylcyclohexane and 47.6 refractoms of toluene. The average total recovery of methylcyclohexane and toluene have not been investigated, but it is anticipated that refractometric adsorption analyses of these materials and other mixtures of saturates and aromatics are possible. COAL HYDROGENATION PRODUCTS
In the adsorption analysis of complex mixtures where the individual components do not emerge from the adsorption column one a t a time, the automatic recording refractometer is a valuable aid in the taking of fractions. In Figure 8 there is shown a refractogram of the adsorption analysis of a neutral oil boiling betFveen 136" and 149" C. from the hydrogenation of coal. Two maxima in the refractogram R ere obtained-the first is associated with displacement development of the saturates, the other by elution development of the aromatics. Ultraviolet spectral analysis of the various fractions of the percolate showed the aromatic compounds, m-xylene and ethylbenzene, t o be present in those fractions collected during the second maximum, but no aromatics present in the fractions collected during the first maximum. Still another example is the adsorption analysis of a similar material with 8. boiling range of 165' to 178" C. As shown in Figure 9, again there ere two peaks in the refractogram-ane by
II I I
\
o
10
1
I 30
20
STATIC PURE SOLVENT
\
,
I
I 40
50
,
1111
1 % 60
EFFLUENT VOLUME IN MILLILITERS
Hefractogram of Methylcyclohexane-Toluene Mixture on Silica Gel
*i c
a 6-X' 0 W
z -
W
2 V
4--
a
EwK
,SATURATES
-
f
z w c1I z
2--
a u
/./
A
A 0
S
IO
2
3
15
4
20
25
30
5
6
7
35
,
8
PERCOLATE F R A C T I O N NO.
Figure 8. Refractogram on Silica Gel of a Neutral Oil from Coal Hydrogenation B.11.136-148O C.
displacement and one by elution. The ultraviolet spectra of these fractions indicated only the presence of indane in the fractions collected during the aromatic or second maximum. The reproducible twin peaks in the saturate maximum may indicate the development of two distinct types of saturate compounds. By comparison of the area under the saturate maximum with the area under the aromatic maximum, it can be shown that there are eleven times as much saturates as aromatics if an average refractive index is assumed for saturates of 1.4200 n?j5O and for aromatics of 1.5000 n2ns'0. SUMMARY
The automatic recording refractometer indicates continuously the changes in refractive index in a flowing stream and if these changes are due to one known component, the concentration of that component a t any given time may be calculated. ils a practical application, this instrument has been used in the quantitative automatic refractometric adsorption analysis of
V O L U M E 24, NO. 7, J U L Y 1 9 5 2
1143
methylcyclohexane and toluene mixtures. This method of analysis is based on the autoniatic recording of the change in refractive index of the percolate during an adsorption analysis and integrating the area under the curve.
=
21
= displacement of phototube in inches = distance from refractometer cell to phototube
T LY
=
d
I
I
I
I
angle of incidence of light as diagonal boundary
= chart divisions = over-all sensitivity
of refractometer expressed m An per chart division, d df = refractomil-i.e., optical sensitivity expressed as An per 1-mil movement of Dhototube: for this instrument m = 1.24 x 10-4 ~n s = recorder sensitivity expressed as chart divisions equivalent to 1refractomil = volume of component (solute) volume of solution containing component nl = refractive index of pure solvent n2 = refractive index of pure component (solute) n, = refractive index of solution A = area under curve in refractogram in chart squares R = rate of flow, chart divisions per milliliter Q = refractom = volume equivalent to 1 refractom v, = volume of component eluted
D I
volume of percolate
2‘
v,
v =
L
I
I
I
I
0
IO
20
30
40
I
EFFLUENT VOLUME IN MILLILITERS Figure 9. Hefractogram on Silica Gel of a Neutral Oil from Coal Hydrogenation B.p. 165-178O C.
,
Furthermore, the method is applicable to any adsorption analysis where the components are eluted singly. Another practical application of the instrument is in the adsorption analysis of complex mixtures in which the components are not eluted singly. The automatically recorded refractogram not only permits the taking of fractions during adsorption analysis according to the development of bands, but also permits rapid comparison of the relative amounts of saturates and aromatics present in hydrocarbon mixtures. Thus, the use of this instrument promises to be of value in adsorption analysis. ACKNOWLEDGMENT
The authors are indebted to A. A. Orning and George Waechter for their advice and technical assistance in this work. NOMENCLATURE
a
= amount of component
c
=
concentration of component
v,
LlTERATURE CITED
(1) Claesson, S., Ann. S. Y . A c a d . Sci., 49, 183-203 (1948). (2) Claesson, S.,Arlziv Kemi Mineral. Geol., 20A, No. 3 (1945).
(3) Dinneen, G. U., Bailey, C. W., Smith, J. R., and Ball, J. S., ANAL.CHEM., 19,992-8 (1947). (4) Hagdahl, L., and Holman, R. T., J . A m . Chem. Soc., 72, 701 (1950). (5) Hurd, C. D., Thomas, G. R., and Frost, A. A., I M . , 72, 3733 (1950). (6) Jones, H., Ashman, L.. and Stahly, E., AXAL.CHEM.,21, 1471 (1949). (7) Kegeles, G., and Sober, H., Division High Polymer Chemistry, Symposium on Physicochemical Methods in Study of High Mo!ecular Weight Xatural Products, 119th Meeting Am. Chem. Sac., Boston, Mass. (8) Mair, B. J., I n d . E m . Chent., 42, 1235 (1950). (9) O’Connor, Ruell, I b i d . , 40, 2102 (1948). (10) Thomas, G. R., O’Konski, C . T., and Hurd, C. D., AXAL.CHEM., 22,1221 (1950). (11) Tiselius, A . , and Claesson, S., Arkiv Kemi Mineral. Geol., 15B, No. 18 (1942). (12) Zaukelies, D., and Frost. -4.A , ANAL.CHEM.,21, 743 (1949). RECEIVEDfor review March 21, 1951. Accepted M a y 5 , 1952. Presented in part before t h e Division of Gas s n d Fuel Chemiqtry a t the 120th M e e t ing of the AMERICAN CHEmcaL SOCIETY, New York, N. Y .
Apparatus for Precise Volumetric Calibration with Adapter to Simulate Natural Drainage WILLIAM K. THOMPSON Dicision of Laboratories and Research, A-ew York State Department of Health, .41bany, 2V. Y .
A
SYSTEhf of calibration has been described (16) that is
based upon equal-volume displacement in a standard pipet or buret, S, and in the apparatus, P , being calibrated. I t differs from others previously developed (1, d, 11) in that measurement in the standard is made with a secondary liquid (mercury) that does not wet its walls; thus a source of variation with a trend toward increasing bias ia avoided. The primary liquid, in the vessel under calibration, may be any that forms a layer upon the secondary; as a rule, it may be considered to be water over mercury. Reilly and Rae described the original apparatus (10); some subsequent modifications ( l a , 16, 18) and an adaptation to microvolumetric measurement ( 1 7 ) have been discussed (2.2). The prasent purpose is to describe the modifications of apparatus and technique in current use, especially with regard to use of an alternative form of the vessel, W , which contains the biliquid
interface, so that naturtil uniestiicted drainage of pipets may be closely simulated in the calibration process. This modification of W , shown in Figure 1 approximately to scale diagrammatically with the rest of the calibration apparatus, differs from the usual vessel W in having a largebore side arm and stopcock, Y (at least 10 mm. in internal diameter), through which drainage from the pipet, P , is allowed to an overflow tube above Y , whence it drains from a trough, T’,through X’ to waste. As needed, water from reservoir R’may be introduced through stopcocks E’ and E and the side arm to W . E’ has e two-way branching system below (not shown in the figure): one to R‘,the other joining a lead from X’that terminates in the neck of a filter flask somewhat above its side arm, which is provided with a tube leading to a sink. The filter flask serves as a trap without blocking drainage from 5’” through X’; if mercury is allowed to flow into the side arm to E, it may be drained through E‘ to this trap. Flexible transparent tubing (Tygon) joins E’ to E and to R’; it is used also to join F’ to the mercury reservoir, R. F’ and F
