A Simple Surface Tensiometer N. B. COLTHUP AND R. E. TORLEY Stamford Research Laboratories, American Cyanamid Co., Stamford, Conn. bubble diameter is negligible for heads up to a decimeter or more of water.
SIMPLE and direct method has been developed for the
A rapid measurement of surface tension.
The equipment required is generally available and the construction is relatively easy. The method has been found to be sufficiently accurate for general usage and it has proved useful as a rapid means of analysis where surface tension values are functions of the concentrations of the component to be determined.
COWSTRUCTIOV AND OPERATIOV
The reservoir and tube may be made of any transparent material of suitable depth, their relative dimensions being dictated only by the volume of liquid available. The choice of the bubble orifice diameter, on the other hand, depends on the accuracy desired, inasmuch as a smaller diameter will lead to a larger meniscus displacement with a subsequently greater accuracy in its measurement.
SLOWLY INCREASING AIR P R E S S U R E
In this case the tube was of soft glass having a 10-mm. bore and 1-mm. wall thickness, and was 35 cm. long. The reservoir was a borosilicate glass tube of 15-mm. bore and was 30 mm. long. The orifice diameter was on the order of 0.16 mm., giving a meniscus displacement of about 18 em. for distilled water. One of the most suitable materials for constructing the orifice is sheet platinum because of the readiness with which it may be wet. A needle was used to punch the hole in the metal and it was then sealed to the soft glass tube at a point about 20 em. from the lower end. If sheet platinum is not available, the orifice may be constructed by thinning a section of the wall of the glass tube and punching a hole with a hot pointed tungsten rod. Because the meniscus displacement may be read best by slowly and steadily increasing the pressure on the system, it is convenient to use a supply such as the laboratory air line or tank gas. If the pressure is properly applied, the meniscus will lower sloivly until bubbling commences, then rise until it ceases. This cycle will be repeated, readings being taken a t each minimum point. In this manner a series of readings may be averaged for optimum precision. In practice it was found that the most suitable rate of depression of the meniscus level for this particular orifice was about 2 or 3 mm. per second. It is necessary to exercise considerable care to keep the orifice clean. -4hot chromic acid bath was found advisable immediately prior to the measurements. A linear scale may be attached to the reservoir or etched on the glass of the tube for measuring the depression of the meniscus level; the latter is preferable from consideration of possible errors resulting from parallax. If the densities of the liquids to be measured are the same or very nearly so, the scale may be constructed to read directly in terms of dynes per centimeter. Similarly, if the surface tension of a solution is essentially a function of the concentration of a given solute, the scale may be calibrated in terms of its percentage.
I 5 TO 30 cm. F O R WATER
MENISCUS
Figure 1 Essentially, the method is an adaptation of the maximum bubble-pressure method, in that the pressure required to force air t h r o q h a submerged orifice is related to the surface tension of the liquid. However, the experimental details are simpler and the effective speed of a determination is somewhat greater. A schematic drawing of the apparatus is shown in Figure 1.
Table I.
I t consists of a reservoir for the li uid to be measured, in which the measuring tube is suspended. %he latter has a small orifice in the side and is adjusted so that this orifice is under the surface of the liquid. The upper end of the tube is attached to a supply of air or any other inert gas such as nitrogen which is available under pressure. The air is admitted to the tube'in a manner such as lowly to increase the pressure until a bubble is forced through the orifice. At the same time the liquid in the lower portion of the measuring tube will be forced out through the bottom and the displacement of the meniscus level below the orifice is read a t the moment that the bubble appears. The surface tension can then be computed from the displacement of the meniscds, the diameter of the orifice, and the density of the liquid. The equation relating the conditions in this system is xgp = 4 y / d where z is the displacement of the meniscus below the orifice a t the moment bubbling occurs, g is the gravity constant, p is the density of the liquid, d is the diameter of the orifice, and y is the surface tension. For all practical purposes, the head of the liquid above the orifice may be neglected, as its effect on the
z,
Surface Tension Values Temp., Measured, ' C. Dynes/Cm. 25.0 26.9
Substance Carbon tetrachloride
Cm. 4.19
Acetone
7.43
25.0
22.7
Benzene
8.27
25.0
28.2
Reported, Dynes/Cm. 26.0 26.16 23.0 22.68 28.1 28.22
References (1)
(3)
[:{
(1) (3)
From several series of twenty measurements each it was found that the standard deviation of the displacement readings was *0.01 cm. The agreement between the theoretical value for the orifice diameter as determined using fresh redistilled water and the value obtained with a microscope was good within the accuracy of the optical method, the two figures being 0.01590 * 0.00002 and 0.0159 * 0.0002 em., respectively. Using the orifice
a04
805
V O L U M E 23, N O , 5, M A Y 1 9 5 1 diameter obtained with water as the standard, the surface tensions of freshly distilled and dried carbon tetrachloride, acetone, and benzene were obtained. The agreements of these with values given in the literature are shown in Table I. Of the literature values listed, those of Andreas, Hauser, and Tucker ( 1 ) mere obtained tiy the pendant drop method, while those reported by Hennaut-Roland and Lek (2) were obtained by the capillary rise method of Richards and Coombs ( 4 ) . N o reference to the method used to determine the surface tension of acetone was given in the handbook (5).
LITERATURE CITED
Andreas, J. M., Hauser, E. A . , and Tucker, W. R., J . Phy,>. Chem., 42, 1001-17 (1938). (2) Hennaut-Roland, hIme., and Lek, M., Bull. soc. chirn. bel^., 40,
(1)
177-94 (1931). (3)
Hodgman, C. D., "Handbook of Chemistry and Physics." 30th ed., p. 1720, Cleveland, Ohio, Chemical Rubber Publishing
(4)
Richards, T. IT..and Coomhs, L. B.. J . A m . C h r m . S o c . , 37, 1656-
Co., 1947. 76 11916). R E C E I V EAugust D 16, 1950
Density-Composition Relation of Mixtures of Trichlorosilane and Tetrachlorosilane ROY I. GRADY, JOHN W. CHITTUM, AND C. K . LYON' The College of F'ooster, Wooster, Ohio H E N trichlorosilane is prepared by passing anhydrous whydrogen chloride over silicon, the product is largely (99% or more) a mixture of trichlorosilane and tetrachlorosilane Depending upon conditions, such as the rate of flow of the gas and the tr,mperature a t which the reaction takes place,, the composition of the product may vary greatly. In this labolatory yield. ranged from 24 to 93% of trichlorosilane, in agreement nitti rwultq obtained hv Booth and Stillwell (2).
by ordinary distillation; through an insulated 17-inch (42.5cm.) Vigreux column; and finally through a carefully insulated 44-inch 17igreux column. Bfter purification, the trichlorosilane showed a constant boiling point, correceed to 760 mm., of 31.731.9" C. and had a density of 1.3415 grams per ml. a t 20" C. Booth and Stillwell (2) found the boiling point of trichlorosilane t o be 31.5' * 0.1" C. a t 760 mm. Stock and Zeidler ( 4 ) gave the boiling point as 31.8" C. at. 760 mm. The tetrachlorosilane was obtained from The Siagara Smelting Corp., Siagara Falls, S . Y. It was redistilled, and t'he portion used had a density of 1.4807 grams per ml. a t 20" C. It boiled constantly a t 56.0" C. a t 735.2 mm. Among the recorded values for the boiling point of tetrachlorosilane is 5i.57' C. a t 1 atmosphere (5). By plotting the data in Table I it becomes possible to interpolat,e for the composition of any per cent mixture in the system a t any temperature between 16" and 27" C. (see Figure 1). Moderate extrapolations to other temperatures beyond this range is possible. The lines are almost linear, indicating a high degree of ideality in the solutions, but not to the extent shown by mixtures of dimethyldichlorosilane and methyltrichlorosilane
(1).
Table I. Densities in the System Trichlorosilane-Tetrachlorosilane I
80 WEIGHT
I
I
60 40 P E R CENT S i H C I 3
I
20
I
0
Figure 1. Densities in the System TrichlorosilaneTetrachlorosilane
SiHCIa, Wt. % 100 75.86 63.28 56.48 47.71 38.68 27.79 19.02 0.0
A simple relation should exist between the density and the composition of this product. It, seemed desirable to prepare a density-composition table for different mixtures of trichlorosilane and tetrachlorosilane a t various temperatures, so that the composition of a given mixture could be quickly estimated. In Table I the densities of pure trichlorosilanc, pure tetrachlorod a n e , and seven weight-per cent mixtures of pure tetrachlorosilane and trichlorosilane are sho\vn a t four different' temperatures: 16", 20", 23', and 27" C. - i l l densities were determined by means of an Ostwald pycnometer with ground-glass caps, and a volume of approximately 22 ml. The trichlorosilane used was prepared in this laboratory by passing anhydrous hydrogen chloride over ferrosilicon a t elevated temperatures. The t,richlorosilane was purified in three stages: 1
Density a t 16' C. 1.3497 1.3805 1.3968 1.4070 1.4186 1.4315 1.4471 1.4599 1.4887
Density a t 23' C. 1.3350 1.3659 1.3825 1.3921 1.4040 1,4169
1.4328 1.4459 1.4746
Density a t 27' C. 1.3264 1.3583 1.3740 1.3836 1.3951 1.4084 1,4241 1.4374 1.4662
To illustrate the use of this graph: X certain mixture having a density of 1.440 grams per ml. a t 18" C. would contain 3oQ/, by weight of trichlorosilane. LITERATURE CITED
Balis, E. W., Gilliam, W. F., Hadsell, E. M.,Liebhafsky, H. A., and \.STinslow,E. H., J . Am. Chem. Soc., 70, 1654 (1948). (2) Booth, H. S.,and Stillwell, W. D., Ibid., 56, 1529 (1934). (3) International Critical Tables, Vol. 1, p. 162, New York, McGrawHill Book Co., 1926. ( 4 ) Stock, A., and Zeidler, F., Ber., 56B,986 (1923).
(1)
Present address, Department of Chemistry, Sorthwestern Cniversity,
Evanston. Ill.
Density at 20' C. 1,3415 1.3733 1.3886 1.3984 1.4104 1.4233 1.4386 1.4519 1.4807
RECEIVED .July 31, 1950
