ANALYTICAL CHEMISTRY
1182 Table XI. Sample No. 1 2 3 4 5 6
Relationship of Per Cent Lead to Line Density % Sn 29.7 33.2 37.5 41.1 47.8 44.7
Table XII. Sample h-0. 1 11 21 31 41 51 61 71 81 91 101 121 131 141 151 161 171 181 191 201 211
%
(Cu f Sb) 0.30 0.30 0.90 0.50 0.80
0.30
Transmittance Obsd. Calcd. 8.7 8.3 8.9 9.0 9.6 10.1 10.6 10.8 12.8 12.3 13.6 13.7
% ’ Pb 70.0 66.5 61.6 58.4 51.4 45.0
Analysis of Tin in Lead-Base Solders Per Cent Tin Yo Deviation from Spec.
Chem.
Chemical Analysis -1.2 f0.3 -0.4 -0.1 -0.3 f0.6 0.0
fl.1 -1.1 f0.8 -0.9
Figure 4. The greatest deviation from the chemical value was 3%. Although the curve is skewed over to the positive side, it is believed that chemical determinations of high tin by the routine method used in the laboratory would tend to give low results due to oxidation of tin by the air. However, this seems insignificant xhen standard deviation of the spectrographic method is *1.0%, including both the chemical and spectrographic errors. ACKNOWLEDGMENT
The authors wish to thank Susan Goyne and A. G. Hartwick for their assistance in the many spectrographic analyses performed. Thanks are also extended to L. Prus of the metallurgical department for the preparation of the standard samples. Finally, the authors are indebted to the members of the chemical laboratory for the large number of chemical analyses made and their cooperation during the course of this investigation.
f0.8
-0.7 -0.8 f0.6 fO.9 -1.0 -2.0 f1.3 4-0.4 -0.1 Standard deviation 1.0
Table XI1 is a comparison of routine spectrographic with the routine chemical analysis. These were taken from a list of 214 determinations which were used to plot the frequency curve in
LITERATURE CITED
(1) American Society for Metals, Cleveland, “LMetals Handbook,” pp. 1525-6, 1939. (2) Churchill, J. R., IND.ENG.CHEM.,ANAL.ED., 16,653 (1944). (3) Dull, B. B., and Hibbert, L. J., J . Optical SOC.Am., 36, 53 (1946). (4) Fast, E.,Ibid., 36,424 (1946). (5) Levy, S., Ibid., 34,447 (1944). (6) Soribner, B. F., J . Research Natl. Bur. Standards, 28, 165 (1942). (7) Smith, D., M., Intern. Tin Research Development Council, Tech. Pub. A , No. 46 (1936). RECEIVED November 3, 1947. Presented a t the Second Annual Symposium of the Analytical Division, Pittsburgh Section, AMERICAIV CE~EMICAL SoCIETY, March 8, 1947.
Determination of Surface Tension of Molten Materials Adaptation of the Pendent Drop Method JAMES K. DAVIS
AND
F. E. BARTELL, University of Michigan, A n n Arbor, Mich.
A simple and apparently accurate method for the determination of surface tension at elevated temperatures is presented. Surface tension measurements on molten glass, resins, waxes, metals, and metallic oxides are described.
T
H E methods that have been successfully applied to the determination of surface tension a t elevated temperatures require special apparatus of varying degrees of complexity. In this article a simple method is described which is particularly applicable to the measurement of surface tensions of molten materials. The method gives precise and reproducible results. The accuracy of these results is dependent upon the assumption that the shape of the molten drop does not change upon cooling and solidification, although the volume and density do change. In the case of isotropic substances this assumption appears to be justified. Where checks with reliable data are possible the value+ obtained are in agreement m7ith such data. The technique is a modification of that employed in the pendent drop method (a). I t consists of heating a small amount of the solid or viscous material until i t melts or flows sufficiently to form a pendent drop. The drop is allowed to solidify and its linear dimensions are measured a t room temperature a t the investigator’s convenience. The surface tension is easily computed from these measurements. The drop itself serves as a permanent record of the investigation. The reliability of the pendent drop method as a means for the measurement of boundary tension has been corroborated by recent work in this laboratory (6, 6 ) .
Figure 1. Method of Selected Plane (2) Linear measurements are made on the solidified drop in accordance Kith the method of the selected planes described by Andreas, Hauser, and Tucker ( 2 ) . The dimensions on which the calculations are based are the equatorial diameter, de, of the drop and the diameter, d,, of a selected plane located at a distance from the apex of the drop equal to the equatorial diameter (Figure 1). The surface tension is calculated from the equation
1183
V O L U M E 2 0 , NO. 1 2 , D E C E M B E R 1 9 4 8
Equation 4 should be used. I n the present work, Equation 4 was used for the calculstion of all surface tensions. EXPERIMENTAL TECHNIQUE
In general, i t is not difficult to obtain reproducible surface tension values for substances which display a reasonably sharp melting point. For these substances, the approximate temperature of drop formation is the melting point. Stable and easily regulated pendent drops result when they are formed either from a tip or from some constriction of the material itself which is considerably narrower than thc maximum diameter of the drop itself. Drops formed from relittively wide bases tend to be unstable when dJd. is less than 1. Since d,/d. becomes meaningless for values greater than 1, no surface tension edculatiotion by the method of the selected plane can be made for such drops. Caution must be taken in forming molten drops of materials such as glass, which have no melting points but undergo a gradual decrease in viscosity with increasing temperature. The viscosity tends to mask the surface tension effects and the pendent drop must be formed by heating in such a manner that the surface tension and not the viscosity is responsible for the size and shape of the drop. This can be accomplished by applying the Source of heat to the drop in such a manner that the portion of the drop ahrive the equatorial diameter receives its heat mnstly by conduction from the heated part of the drop immediately below it. If heat is applied directly to the eonstricted portion of the drop, i t will be elongated under its own n,eight before the surface forces have had ample time to exert their full effect upon its size and shape. The approximate drop formation temperature of materials of this type can be measured with a thermocouple.
or
Substituting the above value of
Figure 2. Pendent Drops Formed by Heating Glass Rods of Various Diameters
8 in Equation 1,
Thus we have an equation for the surface tension nhich involvcs only linear measurements on the solidifieddrop, and the densities. The assumption has been made that the shape of the drop, and hence 1/H, does not change during the cooling process. This, as above indicated, appeirs reasonable in the ease of isotropic substances. If equation 4 is simplified further to
S = PgD:,
a relative error of only
P
(h)
- 1 is introduced.
(5)
Thus the
percentage error introduced by the use of simplified Equation 5 is only approximately one third the percentage difference in t h e densities. Equation 5 is satisfactory for many purposes, but when the density difIerenee exceeds 10 to 15% the more exact
Surface tensions are calculated by means of Equation 2, which requires a knowledge of D,,D,, P, and p . The first two can easily be measured on the solidified drop by means of a c* ordinate comparator. It is advisable on each drop to run individual sets of measurements in two planes normd to each other in order to be assured of the drop's symmetry about its axis of revolution. p , the room temperature density, can be measured without any dimculty, and p can either be actually measured or estimated from data. in the literature, as precise values of p are unnecessary. The data for representative surface tension cal-
Table I. Surface Tension Calculi (3 5-mm. laboratory glass rod. d r w G-4 Normal Plane 1 h De. cm. De, c m
0.4976
DdDs
0.80'3 0.557 2.4'3 337 336
1/H
pP/%l,r
Surface tension, dynedam.
Mesn, dynedom.
0.4026
0.4034 0.810 0 655 2.49
335
1184
ANALYTICAL CHEMISTRY
Table 11. Effect of Rod Diameter on Apparent Surface Tension of a Glass Agproximate Rod Diameter, JIm.
s o . of Determinations
3 5 5
4
6 8
Surface Tension, Dynes/Cm.
3
335 341 334 344 hv. 338
7 4
f
5
culations a t each of t x o normal planes in a pendent drop are given in Table I. RESULTS OF SURFACE TENSION MEASUREMENTS
and density data are given in Table IV. The surface tensions agree within several per cent with those of Bartell and Zuidema (7) when the Harkins and Jordan (9) correction factors have been applied to the latter. A photograph of a pendent drop of Japan wax is shown in Figure 3; a comparison of the sizes of pendent drops of glass and of wax is shown in Figure 4. Resins are also characterized by 1 o ~surface tensions. Samples of polystyrene displayed tensions of about 31 dynes per cm. a t 230" C. Metals with uncontaminated surfaces are characterized by high surface tensions ( 1 ) . The surface tension of electrolytic iron was determined by forming a pendent drop in an atomic hydrogen arc to prevent surface oxidation. The solidified pendent drop is shown in Figure 5. The calculated surface tension was 840 dynes per cm. a t the melting point. Metallic oxides were observed to display considerably lower surface tensions than the metals, in keeping with the known
This convenient modification of the pendent drop method was used to determine the surface tension of glass. Figure 2 is a photograph of pendent drops formed in an oxveen flame a t aoaroximatelv Figure 3. 900" C. a t t h e ends of four glass rods Pendent Drop identical composition. The fact that these of Japan Wax drops have been formed by surface tension forces is evidenced by the agreement of the surface tension values calculated from these four drops, even though the diameters of the rods from Tvhich the drops were formed varied from 3 up to 8 mm. The results of a number of surface tension determinations on each size rod are recorded in Table 11. The average deviation of the individual determinations from the mean value of the surface tension mas about + 2%. The surface tens i o n s of s ~ v ~ r n l Figure 5. Solidified Pendent Drop of Iron Formed in an Atomic Hydrogen Arc
df
dimes
130 to 160 per cm. to 400 to 500 dynes per cm. ( I d ) . More recently, however, fairly close agreement has been obtained by various investigators (3, 4, 8) using different methods of measurement. These values are in the neighborhood of 300 dynes per cm. and are in line with those of Table 111. The surface tension of a glass depends on its composition. Examination of Table I11 reveals something of the nature of this relationship.
Figure 4. Comparison of Pendent Drops of Glass and of Wax
Glass A-6 differs from A-5 chiefly in that it contains about 5% potassium oxide, whereas Q-5 contains no potassium oxide but about 5% more sodium oxide. The substitution of this amount of potassium oxide for sodium oxide has resulted in a considerably lower surface tension. Glass -4-7 contains no potassium oxide and an amount of alkaline earth oxides comparable to that of A-5. Its surface tension is about 10% above that of A-6 and somewhat above that of -4-5. S-1 is a ground coat enamel kindly furnished by Harrison (11). Its low surface tension can be attributed in part a t least to its high boron oxide content. The surface tensions of several waxes, all of which exhibited fairly ion- surface trnuions a t their melting points, were investigated. The surface tensions, temperatures of drop formation,
Figure 6. Pendent Drop of Lead Chloride
fact that formation of o\ide films on metals reduces their surface tensions to a marked degree. The surface tensions of lead oxide and antimony trioxide a t their respective melting points were found to be 157 and 98 dynes per cm. The surface tension of lead chloride (136 dynes per cm. a t its melting point) was even lower than that of lead oxide. Pendent drops of lead chloride and antimony trioxide are pictured in Figures 6 and 7, respectively. I t is interesting to note in Figure 7 that the needles of antimony trioxide which formed upon solidification are oriented normal to the surface. The formation of these needles reduces the precision of the linear measurements made on the drop. The exact limits of accuracy of the method can be determined
Surface Tensions of Silicate Glasses 4-5 A-6 A-7 s- 1
Table 111. Glass SiOt, % Ua,O
%
k o , '%
72 4 13.3
71.5 8.5
9.2 3.4
13.5 0.1
1.1
0.2
...
CaO, %
mo,%
...
...
BnOs,% AltOl, % Fe % cob, %
... ...
Temp. (approx.), Surface tension, dynes/cm.
C.
Table IV. Kind Parawax Japan wax Beeswax Carnauba wax
Temp.,
c.
50 45 62 85
71.5 12.9
...
12.11 2.5
I
...
0.2
...
... ..
...
40.9 15.3 4.5 8.4
...
17.5 7.7 3.5 0.6
goo
900
900
7511
334
312
344
262
Surface Tensions of Waxes S,
P
P
Dynes/Crn.
0.885 0.970 0,960 0.996
0.781
26.1 29.9 29.4 29.3
0.899 0.835 0.832
V O L U M E 20, NO. 12, D E C E M B E R 1 9 4 8 only through further study. I t is believed, holvever, that this method can bt. used to advantage for the determination of approximate surface tensions of substances Lvhich have a relatively high mrlting point and for those which tend to flow upon heating but do not have sharp and well-defined melting points. Measurements are simplified, as it is not necessary to make them with the material maintained a t a high temperature. ACKNOWLEDGMENT
1185 LITERATURE CITED
Figure 1. Pendent Drop of Antimony Trioxide Note orientation of needles
formed during The values for lead oxide and lead crystallization chloride were determined in these laboratories by George F. Dasher. The density value used for lead oxide was 8.02 (at 9280c.) w;hichwas kindly furnished by W. X. Harrison (10). This value is Presumabl?. close t o the density value of oxide at its melting point, 888” C. The authors .i?.ishto express their thanks to the Corning Glas? Works, K m b l e Glass co., Libbey-Owens-Ford co., and Pittsburgh ’late ‘lass for and Of glasses in the course of this investigation.
(1) Adam, S . K., “Physics and Chemistry of Surfaces,” p. 161, Oxford, Clarendon Press, 1930. ( 2 ) Andreas, J. M., Hauser, E. H., and Tucker, W.B., J . Phys. Chem., 42, 1001 (1938). (3) Babcock, C. L., J . Am. Ceram. Soc.. 23. 12 (1940). (4) Badger, A. E., Parmelee, C. IT.,and Williams, A. E., Ibid., 20, 325 (1937). ( 5 ) Bartell. F. E., and Davis. J. K., J . Phw. Chem.. 45, 1321 (1941). (6) Bartell, F. E., and Kiederhauser, D.-O., “Corrected Table for Calculation of Boundary Tensions by Pendent Drop -Method,” Am. Petroleum Inst., Project 27, unpublished. ( 7 ) Bartell, F. E., and Zuidema, H. H., J . Am. Chem. Soc., 58, 1453 (1936). (8) Bradley, C. A., Jr., J. Am. Ceram. SOC.,21, 339 (1938). (9) Harkins, W. D., and Jordan, H. F.. J . Am. Chem. Soc., 52, 1751 (1930). (10) Harrison, W. N., National Bureau of Standards, private communication. N.9 and A f O O r e , D. G.9 J . Research A r d . BUT. (11) Harrison, Standards, 21, 337-46 (1938). (12) hIorey, G . w., ”properties of Glass,” p . 210, . ~ M E R I C A NCHEMICAL SOCIETY Monograph, New York, Reinhold Publishing Corp., 1938. December 1Q47. presented beiore the Division of Colloid Chemistry at the 100th Meeting of the . ~ M E R I C A X CHEMICAL SOCIXTY, Detroit, Bfich. RECEIVED
COZYMASE Assay of Diphosphopyridine Nucleotide Preparations SIDNEY GUTCHO AND EARL D. STEWART, Schwarz Laboratories, Inc., New York, N . Y Assay of cozymase preparations for diphosphopyridine nucleotide content by reduction of the diphosphopyridine nucleotide and measurement of the light absorbed at 340 mp by the dihydrocozymase formed was first carried out by Warburg and Christian. With modifications such as those suggested by LePage (3), for example, the method is in very general use. Other methods for estimating coenzyme I have been reviewed by Schlenk and Schlenk (7). A manometric oxygen absorption method has been proposed by Krishnan (2).
B
EC2iUGE of the brief time required for its completion,
the spectrophotometric method is well suited in principle to the assay of cozymase preparations, for both control and standardization purposes. \Then applied repeatedly to the same or similar preparations, however, absorption methods yielded results for the diphosphopyridine nucleotide (DPX) content of cozymase that varied appreciably Kith the F a y in which the reduction was performed. The procedures of Karburg and Christian (8, 9) were studied, therefore, to see n hat factors affected reproducibility and maximum light absorption. The method of assaying cozymase preparations presented here is based on the effects of temperature, time of reduction, and concentration of reducing agent, found in these studies. I t has been applied to materials of widely varying diphosphopyridine nucleotide content with consistent and reproducible results. For study of the conditions necessary for good reproducibility and ma\imum absorption, several grams of cozymase of approximately 507, diphosphopyridine nucleotide content were prepared by a modification of the method of Williamson and Green (IO) and set aside for use in the experiments. All determinations of time and teniperature effects Tvere thus made on the same material, and are reported on an “as is” basis. REAGEYTS
Sodium Hydrosulfite Reagent. A 0.27, solution of sodium hydrosulfite in 1.07, sodium bicarbonate is freshly prepared for each series of determinations by dissolving 100 mg. of sodium hydrosulfite and 500 mg. of sodium bicarbonate in 50 ml. of distilled water in a volumetric flaek. The sodium hydrosulfite, Pure Powder, was obtained from the Amend Drug and Chemical Co. and analyzed 86% sodium hydrosulfite by iodine titration (4).
Sodium Bicarbonate-Sodium Carbonate Buffer, pH 9.7, a ’ sodium bicarbonate and 1% anhydrous solution containing 1% sodium carbonate. APPARATUS
A Beckman quartz spectrophotometer, model DU, with 1.00em. absorption cells, is used. The aerating device is a 25 X 200 mm. test tube which can be stoppered by a two-hole rubber stopper holding a glass-tubing vacuum outlet and a glass-tubing air inlet, the inner end of which extends to the bottom of the test tube and is closed down to a 1-mm. bore, approximately, while the outer end is fitted with a short piece of rubber tubing and a screw clamp. By using Y-tubes several test tubes can be connected to a single vacuum valve. METHOD O F ANALYSIS AND CALCULATION
The following extremely rapid procedure yields mavinium reproducible reduction of the cozymase to dihydrocozymase. Two milliliters of the sodium hydrosulfite reagent are added to approximately 10.0 mg. of cozymase, previously weighed and transferred to a 13 X 100 mm. test tube. (In the experiments on effects of time and temperature, 12.5-mg. samples were assayed.) The tube is immersed immediately in boiling water for 1 minute. During the minute of heating the complete solution of the cozymase is effected rapidly while the initial yellow color (nionohydrocozymase), which appears instantly on adding the reagent to the cozymase, fades out within 30 seconds. Particles of cozymase, which may be caught within the slight foam that forms during heating, should be brought into solution by gentle shaking After 1 minute, the tube is removed from the boiling water bath and immersed in an ice water bath, and enough sodium bicarbonate-sodium carbonate buffer is added nearly to fill the tube. After 30 seconds, the chilled solution is diluted further to 50 ml.
