V O L U M E 21, N O , 6, J U N E 1 9 4 9
149
C
Minute Treatment on Mincing Apparatus
Jhows the "before and after" a p e & of 2 poulldv of fresh mature navel orange peel segments subjected to a l-minute trerttment in 1800 ml. of benzene, then filtered. It. was found empirically that under the author's conditions 2 ml. of solvent per gram of fresh material sufficed for most plant. parts-ex., alfalfa, hark,
LITERATURE CITED
(1) Bemle, E. J., J . Assoc. OBc.Agr. Chemists, 25,573 (1942). (2) Comar, c. L.. Miller, E. J., Richard, M. N., and Benne, E. J., IND. ENC.CHEM.. ANAL.Eo.. 16,717 (1944). (3) Davis, W. B.. Ind. Eng. Chem., X m s Ed., 17,752 (1939). R~~~~~~~ aeDtember2, lo4*.
Trap for Determination of Water by the Distillation Method EARLG R. CALEY AND LOUIS GORDON', Ohio State University, Columbus, Ohio
HE types of traps commrroially available for the determinaTtion of water hy distillation of samples with an immiscible liquid of low density, such as t,oluene, are in some respects unsatisfactory. Wit,h a trap such as that of Bidwell and Sterling (2),having a graduated port,ion with a hare sufficientlysmall to obtain reasonably precise readings of small volumes, sharp separation of the immiscible liquid and the water often does not occur even when the trap has been carefully cleaned. Droplets I
of water may adhere to the glass and fail to coalesce, or alternate slugs of immiscible liquid and wat,er fill the graduated tube so that sharp separation must be brought about by some mechanical means. Sharp separation usually occurs in traps that have graduated tubes of larger bore (S),hut this involves !a sacrifice of precision in reading the volume of water.
A trap of the design shown in Figure 1 combines the advantares
Present address, Syraciiie University, Syracuse, N. Y .
the mercury is brought u p i n t o t h k wider G%rtof the trap while the water is distilling over. As soon as all the water has distilled over and sharp separation has occurred, the mercury level is lowered so as to draw the wat.or down into the graduated art for measurement. The water is almost invariably drawn at once into the narrow graduated tube sharply and cleanly, hut if t,his does not occur because the tube is not clean, two or three raisings, or lowerings of the mercury levcl will by mechzniesl action bring about a sharp separation.
dwn
This principle of operation is not entirely new; the same idea was, employed by Beckel, Sharp, and Milner (1) in an apparatus
Figure 1. Improved Trap for Collecting and Measuring Water
tor the determination of water by distillation. However, these workers do not appear to have realized the full potentialities of this principle of operation, nor did they test i t critically, or mention the existence of one difficulty connected with its practical application. By means of this principle of operation, traps with graduated tubes of considerably smaller bore may he used than is possible otherwise. It was found possible to draw down collected water from a wide tube into a tube having a bore of only 1 mm. Hawever, the use of a graduated tube of such small diameter is not very satisfactory for the separation of water and an immiscible liquid such as toluene over a mercury surface. In spite of the fact that water dropping onto a mercury surface covered with toluene appears to displace the toluene completely, so that only water remains in contact with the mercury, a very thin fdm of toluene adheres tenaciously to the mercury surface. If the mercury level is then lowered so as to bring the water layer completely into the narrow tube, the fdm of toluene contracts &s the surface area of the mercury decreases, and i t finally forms a droplet of varying size a t the water-meroury interface. This causes an uncertainty in reading the volume of confined water. If the tube is not too small in diameter this droplet may he displaced from the mercury surface and made to rise into the toluene layer by means of the device shown a t the bottom of the graduated tube in Figure 1: a thin rod of glass or stainless steel centrally placed in the lower part of the graduated tube, and mounted
ANALYTICAL CHEMISTRY
750 Table I. -4pparent Change in Volume of Given Quantity of Water Passed Five Times from Upper Part to Graduated Part of Trap Di.~~ ffePenrP ~. ~.. .. between Initial and Greatest ~ Final ~ l Observed Reading Difference ~
Initial Reading
Intermediate Readings Highest Lowest
0.20 0.44 0.95 1.91 2 89 3.88
~ i Reading
0.20 0.42 0.93 1.91 2.89 3.88
0.21 0.43 0.94 1 91 2.91 3.88
0.00 0.02 0.01 0.00 0.00 0.00
0.20 0.42 0.94 1.91 2.89 3.88
0.01 0.02 0.02 0 00 0.02 0.00
Table 11. ,igreenient of Duplicate Determinations K a t er Taken
Tube Reading
Correction
Water Recox ered
Difference between Duplicates
2.00 ?.00 3.99 3.99
1 91 1 00 3.90 3.88
0.c9 0.09 0 11 0.11
2 00 1.09 4.01 3.99
0:01
0:0?
Table 111. Determination of Water in Hydrated Barium Chloride (Determined gravimetrically and by distillation) Samples taken, g. 1.5301 6.4936 13.72 .. .. . . . ., 1.91 Tube readings, ml. .. ,, ...,. 2.00 Corrected volumes of water, nil. Derived weights of water, g. . ,. 1.99 Loss of weight on heating, g . C ' 2ii2 0.9490 Water found, % 14.59 14.61 14:i
17.65 2.48 2.58 2.57
...
14.6
0.11-
0.10
-
0.09-
z
0
F
0.06-
0
W
K
e 0
0
0.07-
0.06
-
0.05
I
I
0.00
I.oo
APPARENT
VOLUME
Figure 2.
I
I
2M)
300
OF WATER
4
COLLECTED, ML.
Calibration Graph
with rubber tubing so that its flat tip may be displaced horizontally. When the mercury with such a droplet on its surface is lowered past this obstruction it is knocked off at once and rises to the top, or a slight adjustment of the position of the top of the rod will cause its removal when the mercury is again lowered. There is also a lower limit to the volume of water that may be successfully drawn down from a wide tube into a narrOw tube. If the water is so small in volume that it does not form an intact layer be-
tween the toluene layer and the mercury surface in the wide tube, the toluene tends t o be drawn past the water when the mercury is lowered into the narrow tube. Because of this difficulty the volume of water collected should not be less than about 0.20 ml. The trap used for the test experiments described here had as its basis a 5-ml. Pyres measuring pipet with an internal bore of 5.5 mm. As shown in Figure 1, it is important for successful operation that the connection between the wide tube and the narrow graduated tube be gradually tapered. The capacity of that part of the trap between the inlet tube and the top of the graduated tube should be at least twice and preferably three times that of the graduated tube itself. In calibrating traps of this type for accurate work it is not sufficient to determine the capacity by volumetric calibration n.ith water. In actual operation the volunie of the collected water is most conveniently read between the bottom of a water meniscus at the toluene-water interface and the top of a mercury meniscus a t the water-mercury interface, thus involving a considerable meniscus error if the usual method of calibration is taken as the basis. Moreover, in a given apparatus there is a slight but appreciable loss of water due to imperfect condensation or to loss at the groun+glass joints that increases with increase in the amount of water distilled over. I t is far better, therefore, to calibrate the graduated tube on the basis of actual runs in which accurately measured or weighed portions of water are distilled in the apparatus and compared with the apparent volumes read in the trap. The data thus obtained are used to construct a convenient calibration or correction graph (Figure 2 ) for the apparatus used for the esperiments here reported. The results in Table I indicate that no appreciable losses are caused by repeated transfer of the collected n-ater from the upper to the lower part of the trap. Table I1 shows the agreement obtained in duplicate runs, in which the stated volumes of vater were measured into the distilling flask with a calibrated pipet. The small differences found in both these sets of esperiments probably represent observational error in reading volumes rather than error of method. Table IIT shows the outcome of test determinations on a uniform lot of hydrated barium chloride. The water content found by distillation agrees well Tvith the accurate gravimetric results found by loss on oven drying. It is inconvenient and unnecessary to dismantle traps of the type described here after each determination for treatment Kith cleaning solution, as is the common practice iTith the usual type of trap.
It is sufficient first to disconnect the distilling flask, place a small beaker under the inlet tube, and raise the mercury so as t o expel nearlv all the water and toluene or ot,her immiscible solvent. Any residual t,oluene may be largely removed by flushing out with distilled water. Grease-free acetone is used to flush out the water without changing the level of the mercury. Then the mercury is lowered to the bottom of the graduated tube and t'his is filled with acetone. By alternately raising and 1oTvering the mercury from the bottom to the top of the graduated tube three or four times the walls are freed of water and thoroughly cleaned. The mercury is then raised so as to expel most of the acetone into the collecting beaker. Finally, the residual acetone is allowed to evaporate spontaneously, or the inlet tube is stoppered and suction is applied to the top of the trap so as to evaporate the acetone rapidly. Any mercury accidentally spilled in the cleaning operation will be caught in the beaker and may be returned to the leveling apparatus. This method of cleaning lends itself well to the operation of a series of setups for the determination of water by the distillation method. LITERATURE CITED
(1) Beckel, A. C., Sharp, A. G., and Milner, R. T., IXD. ENG.CHEM., ANAL.ED., 11, 425-6 (1939). (2) Bidwell, G. L., and Sterling, TV. F., Ind. Eng. Chem., 17, 147-9 (1925). (3) Dean, E. W., and Stark, D. D., Ibid., 12,486-90 (1920).
RECEIVED March 30, 1948.
