400
INDUSTRIAL AND ENGINEERING CHEMISTRY
ters, one containing Apiezone-A,' and the second light mineral oil (white paraffin oil, U. S. P., Eimer and Amend Co., New York, N. Y.); the mercury-oil manometer previously described ( I ) , using Apiezone-B;l a Zimmerli vacuum gage (3); and a webmade, simple U-type mercury manometer. I n order to ensure constant pressure during each set of observations, a pressure-control unit (2) was used in the system with the communicating tube placed a t a point equidistant from all the gages. Readings on the Zimmerli gage had to be made with considerable care, and were time-consuming because of the need to ensure accurate adjustment of the levels for each observation. However, with the aid of automatic pressure control, constant pressure was maintained a t each point of observation, and with some practice it was possible to obtain readings with an error not exceeding 0.1 mm. of mercury, as shown by comparative readings. 1
.&piezone-A and Apiezone-B (J. Biddie and Co., Philadelphia, Pa.).
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Readings of the simple mercury C-manometer were accurate to about 0.3 mm. Calculated values in Table I were obtained by dividing the oil readings by the ratio of density of mercury a t the room temperature to that of oil a t the same temperature. TABLE11. RATIOOF DENSITY OF MERCURY TO OILS Oil Used hpiezone-B Apiezone-.I Mineral oil
Equivalence of 1 mm. H g in Terms of Oil .It 20' C. A t 25' C. At 30' C. I t 35" C. 15.54 15.58 15.63 16.67 15.55 15.73
15.59 15.78
15.64 15.83
l5,68 15.87
I n Table I1 are given data on the equivalence of mercury to oil readings a t the temperatures indicated.
Literature Cited (1) Palkin, S., ISD. EXG. CHEM., Anal. Ed.,7,434 (1935). (2) Ibid., 7,436 (1935). (3) Scientific Glass A p p a r a t u s Co., Item 19,115,p. 108,1936 catalog. RECEIVED March 2 3 , 1938.
Improved Trap for JMoisture Determination by Distillation J
EARLE E. LANGELAND AND RICHARD W. PRATT Union Paste Company, Medford, Xlass.
I
N DETERhIINISG moisture in materials by distillation with an immiscible liquid, certain advantages are to be gained by the use of a liquid heavier than water. In the case, for example, of tetrachloroethylene (1) the high specific gravity of the solvent permits most of the materials to be dried to float a t the top of this liquid, preventing localized overheating and charring which frequently take place when lighter distilling liquids are used, and (2) there is complete freedom from fire hazard. Because the water which is to be measured floats on top of the distilling medium in the trap, when liquids heavier than water are used for this purpose, i t is not possible to effect the necessary return of solvent to the boiling flask by means of overflow, as in the Dean-Stark trap, and a different principle must be employed. il trap to effect this result has been described by Bailey ( 1 ) in which a tube connects the boiling flask with a stopcock sealed into the bottom of the graduated trap. I n operation, when steady conditions have been reached, the stopcock is opened just enough to permit the distilling medium to return to the boiling flask a t the same rate it is received into the trap from the condenser. I n using the Bailey trap one primary difficulty confronted the authors. Because of unsteady and widely fluctuating thermal environment, which was not susceptible of easy control, constant manipulation of the stopcock was required during a determination to prerent complete drainage of the trap or the overflow of the water a t the top. This difficulty led them to produce the trap pictured in Figure 1, in which all trouble from unsteady thermal conditions was eliminated. Once the water has been received in the trap it is impossible for it to return to the boiling flask under any reasonable conditions of heating. When the apparatus has been set up and the heat applied to the flask, no further attention is required until the completion of the distillation.
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15MM OD
FIGURE1. DIAGRAM OF RECEIVING TRAP
JULY 15, 1938
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I n its basic principle this trap is similar to that used for determining crankcase dilution according to A. S. T. PI. method D322-35. It has been modified to accommodate it to the different specific gravities of the liquids employed.
Design of Trap The diagram, Figure 1, is self-explanatory in all but one particular. The entrance of reflux return tube A into vapor tube B should be fixed at a specific point peculiar to the distilling medium used. This point is determined by the ratio of the specific gravity of water to that of the distilling liquid employed. This ratio, multiplied by the number of milliliters in the entire graduated portion, gives the milliliter reading opposite which the lower point of the reflux return tube junction with vapor tube B should be. In the case of tetrachloroethylene, having a specific gravity of 1.6, this ratio is 0.62, and hence, with a 10-ml. trap, the point of entry of the return tube should be opposite the 6.2ml. mark, as is shown in the diagram. Unless this junction is so placed, wit,h some volumes of water, near the maximum capacity of the apparatus, one meniscus will be off the graduated portion. Reading of Meniscuses To determine the volume of water distilled over from the sample two meniscuses must be read: an upper water-air interface, and a lon-er water-tetrachloroethylene junction. The reading of the upper water-air meniscus in both the Bailey trap and the authors' was rendered difficult because a drop of tetrachloroethylene customarily remained suspended upon the top of the water layer, apparently because of the surface tension of the water. Such a drop is shown clearly in Figure 2'4, a t the upper meniscus. Shaking and bumping seldom served to dislodge this drop in its entirety and another expedient was necessarily employed. When the distillation was completed and the water in the trap had cooled to about room temperature, the condenser was disconnected and swung aside. One very small drop of a surface tension depressant, Tergitol4 ( 2 ) ,was added carefully from a capillary dropper. This served immediately to cause the pendant drop of tetrachloroethylene to be released from the water surface, rendering the water-air meniscus entirely normal and easily read (Figure 2B). The reading should be taken rather soon after the addition of the Tergitol 4; otherwise a tendency to clouding on standing renders the reading difficult. The volume of water is not measurably increased by the addition of the necessary amount of surface tension depressant. Another material of similar nature, Tergitol 7, did not appear to be suitable for this purpose. TABLEI. DETERMINATIOS OF WATER Sample
0
Amount Taken
Water 8 ml. CuSOa 5HzO 20 grams Starch 50 grams Recovery in trap 7.98 ml.
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-water By tetrachloroethylene
By toluol
Found-
BY oven a t 105' C.
%
Y O
%
99 750 27.2 13 36
27 '0 13 4
13'5
A second beneficent effect of the Tergitol 4 addition was noted a t the lower water-tetrachloroethylene meniscus. Before the addition of this agent the meniscus here is concave downwards, and for a water-calibrated trap the reading must be taken a t the cusp of the crescent. This concavity is noticeable a t the lower meniscus in Figure 2A, but is less pronounced than is frequently the case. I n order t o secure contrast for photographic purposes, it was necessary to color the tetrachloroethylene with lampblack in oil, and this coloring material showed a tendency to level out the interface. However, upon adding the drop of Tergitol 4, this lower meniscus flattens out and a perfectly level interface obtains when the proper amount of the surface tension depressant has
A
B
FIGURE 2. RECEIVING TRAPCONTAINIKG WATER A . Before addition of Tergitol B. After addition of Tergitol
been added. This junction is extremely easy to read, as is apparent from Figure 2B, and in conjunction with the familiar water-air meniscus a t the top renders the determination of the volume of water entirely satisfactory.
Accuracy and Precision The accuracy of the method has been determined by measuring the volume of water recovered in the trap when a known volume of water is added to the flask and distilled over (Table I). The precision of the method has been determined against two standard methods with one material, and against one standard method with another. These data are also given in Table I. The percentage of water found in the copper sulfate is slightly lower than the theoretical for 4 molecules of water (28.8 per cent), which should come off a t the temperature of boiling toluene or tetrachloroethylene. Since the two methods check well on this dcltermination, the obvious explanation is that the crystals used were slightly dehydrated, but this point has not been determined. The trap may be calibrated so as to require the reading of only one point to render the volume of water directly rather than by the difference of two readings. A consideration of the nature of the balance between the column of tetrachloroethylene in the reflux return line and the water-tetrachloroethylene column in the graduated portion indicates that for any given volume of water between zero and 10 ml. the lower (water-tetrachloroethylene) interface will be a t some point between zero and 6.2 ml. on the graduated scale, and that the location of this point will be dependent upon the volume of water present. Hence, if the point now marked zero is marked 10 ml., the present 6.2-ml. point is changed to zero, and the intervening space is graduated, a single reading will suffice to indicate the volume of water. Two disadvantages of this method of calibration should be pointed out: The accuracy of the reading mill be conditional upon a constant
ISDUSTRI.4L AKD ENGINEERING CHEMISTRI-
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ratio of specific gravities between the water layer and the tetrachloroethylene layer; and any change in the ratio will vitiate the reading. Furthermore, the scale is shortened in length which in turn renders the reading somewhat less accurate.
Summary A trap is described which is suitable for use in determining moisture by distillation with immiscible liquids heavier than
VOL. 10, NO. 7
water. Its operation is independent of thermal environment, and requires no adjustment of reflux rate. The use of a surface tension depressant facilitates the correct reading of the water volume.
Literature Cited (1) Bailey, A. J., ISD. ENG.CHEY.,Anal. Ed., 9,568 (1937). ( 2 ) Wilkes and Wickert, INDENG CHEM.,29, 1234 (1937). RECEIIE D Xlarcli 2 2 , l Y 38.
An Easily Constructed Orifice CHESTER P. BAKER
ARD
WILLIAM -4. RIcGRATH
Northeastern University, Boston, Mass.
T
HE velocity of a fluid in a pipe line may be determined
by inserting an obstruction and measuring the change in static pressure resulting from the change in the velocity produced by it. The relationship between the size of the obstruction and the pressure drop is convertible into the line velocity. The standard orifice makes use of this principle.
'J-
B type of orifice construction which has been found very satisfactory is shorn in the drawing. A close examination will reveal that the flanged castings of the standard orifice have been replaced by an ordinary union threaded throughout its length with a shoulder formed by the pipe in the female side to hold the orifice plate. The threaded straight sections of pipe extend to the orifice plate. The pipe ends may be machined or a lead gasket used to make a water-tight bearing between the pipe and the orifice diaphragm. Proper machining will allow the orifice plate to be held rigidly and a t the same time not lose the advantage of the ground joint of the union. When a lead gasket is used, a tight joint can be made which is satisfactory a t low pressures. RIanometer openings
can be drilled and tapped without difficulty after the other parts have been assembled. The orifice described can be constructed from ordinary pipe fittings with the minimum of shop equipment. The interior of the orifice chamber is smooth without expansion and contraction areas near the manometer openings. The
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orifice plate can easily be removed and the fluid allowed to flow through the line without the resistance of the orifice. The centering of the orifice ceases to be a problem in this type of construction, once the orifice opening has been made in the exact center of the disk which serves as the orifice plate. Care should be taken as with other types of orifices t o insert it in a straight pipe of sufficient length to equalize the turbulence caused by fittings such as elbows, tees, etc. The authors have found this type of orifice to be easier to construct, less expensive, and more accurate than others which use castings t o form the orifice chamber. RECEIVED April 9, 1938.
