T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
496
+ +
b(2 c-t) 1 5 ( 2 c - 6) - 30 c-go 90 = 50 c 160 1z=
go =
250
+
p(2
c-t-
10(2
20
c-
c
I)
- 6 - I)
= 50 c
c = 5 If, however, PZ had been 60 min: instead of go min. the value of c would have come t o 4.4; this would mean t h a t either 5 cells would have t o be used with a wait of 30 min. after charging before t h e first batch of solvent is ready t o run on or else t h e time of boiling or of pumping would have t o be lengthened so t h a t 4 cells could do t h e work. If, for instance, 4 cells are t o do t h e work, the boiling period must be lengthened t o 2 5 min. 60 = b ( 8 - 6) 1o(8 - 6 - I ) 60 = 2 b IO b = 25 or the pumping period t o 30 min. 60 = 15(8- 6) p ( 8 - 6- I) 60 = 30 4- p
+
+
+
p
= 30.
These examples show t h e method of using the formula in determining t h e number of cells required under different conditions of treatment. COMPARISON O F SIMULTANEOUS AND SEPARATE P U M P I N G SYSTEMS
The formulas also make it possible t o compare t h e time consumed between discharges when pumping simultaneously with t h a t consumed when pumping separately, other conditions of extraction being t h e same. If we take, for instance, a series of 6 extractions in 4 cells, b = 15 and p = 5. With separate pumping t z will be 15(8- 6) 4(86- 5)s (12 4)s = 30 - 60 S o = 50 a will be 30 (6 1)s = 65, and 6-2 e will be 15 p = 25.
+
+
+
+
+ + +
~
2
For a comparison i t would not be fair t o use b with t h e same value in simultaneous pumping as in separate pumping because in t h e latter case, in t h e example just given, although b is 15, t h e actual total boiling 2 p ) ; in order time for each charge, e, is 25 min. ( b t o have conditions t h e same in t h e two systems, therefore, the value of b in simultaneous pumping (which is always the actual total time of t h e boiling) must be 2 5 min. With c = 4, t = 6, b = 2 5 , and p = 5 in simultaneous pumping TZ = 25(8-6) 5(S-6-1) = 50 5 = 55 a = 2 b + z p = 5 0 + 1 0 = 6 0 e = b = 25. T h a t is, a, t h e time required between successive discharges of material is a little less in t h e case of simultaneous pumping.1 But there is a practical consideration which changes this relation slightly; pumping several cells a t t h e same time is likely t o take
+
+
+
1 Although this is only one case it may be shown that the difference between o (sep) and a (sim), with other conditions the same, is always P
when t is even and?t
9 when f is odd.
12,
No. 5
longer t h a n pumping a single cell, and therefore if 16 = 66 min., and p (sim) = 8, then a (sim) = 50 a (sep) = 30 3 5 = 6 5 min., t h a t is, when t h e pumping time is increased a little t o allow for the increased difficulty of pumping several cells instead of one cell, t h e time required for a complete cycle may be the same or even less in t h e case of separate pumping.
+
+
70
Vol.
SUMMARY
I-Formulas have been developed which show t h e relation between the number of cells and number of treatments in terms of various typical extraction operations both for separate and simultaneous pumping of t h e solvent in t h e cells. The formulas for simultaneous pumping are also applicable t o continuous extraction processes. 2-These formulas make i t possible t o determine t h e number of separate cells or extractors required t o furnish a certain number of treatments or extractions for each charge when t h e time required for each of t h e various operations is known. 3-With t h e formulas t h e time relation between simultaneous pumping and separate pumping has been developed, showing no advantage or very slight advantage for t h e former. VAPOR COMPOSITION OF ALCOHOL-WATER MIXTURES By W. I(. Lewis RESEARCHLABORATORY OF APPLIEDCHEMISTRY, MAS3ACHUSSTTS IN-! STITUTE O P TECHNOLOQY, CAMBRIDGE, MASS. Received December 18, 1919
I-n t h e field of distillation there is no more important problem t h a n t h e separation of ethyl alcohol from aqueous solutions. Accuracy in t h e design of apparatus for this separation is absolutely dependent upon exact d a t a as t o the composition of the vapors given off by any specific mixture of t h e two liquids. The d a t a on this point hitherto available in t h e literature have been inadequate and unreliable. The figures usually accepted are those recalculated for Maerckerl by Donitz from t h e original experimental results of Groning. These d a t a check reasonably t h e results obtained a half century ago b y Duclaux.2 The more recent work of Sore1 does not check t h a t of Groning and is apparently less reliable. The work of Evans3 is obviously unreliable in view of t h e fact t h a t he finds t h e composition of vapor and liquid identical a t 92 per cent b y weight, whereas a distillate of higher than 95 per cent alcohol can be obtained in commercial practice. I n 1913 Wrewsky4 published the results of a series of careful determinations of t h e vapor composition of alcohol-water mixtures, which bear t h e earmarks of reliability. On t h e other hand, Wrewsky’s work was done, not a t constant pressure, b u t a t constant temperature. Furthermore, he operated at only three temperatures, approximately 40°, 5 5 O , and 75’ C. His work is, therefore, not directly available for industrial practice because the industrial distillation “Handbuch der Spiritus Fabrikation,” 7th Ed., Berlin (1898), 590. (1878), 3 0 5 . STHIS JOURNAL, 8 (1916), 261. 4 Z . phys. Chem., 81 (1912), 1 . 1
* Ann. chim. Phys., 14
1920
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E i M I S T R Y
of alcohol is carried on entirely a t temperatures above 78", k. e . , a t atmospheric pressure and, in the bottom of rectifying columns, even higher. I n order t o make these d a t a available for industrial use we have recalculated Wrewsky's results, extrapolating t h e m up t o t h e boiling point. T h e resulting d a t a are given graphically in t h e accompanying plots and are believed. t o be b y far t h e most-accurate figures avail-
49 7
able on the vapor compositions of alcohol-water mixtures. A t each of t h e temperatures mentioned above Wrewsky determined t h e vapor composition curve. From these isothermal curves t h e vapor composition was read off a t stated intervals of liquid composition and, for each definite liquid composition, plotted against the temperature. These temperature curves
498
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
were extrapolated up t o the boiling point of t h e liquid in question. This gave t h e vapor composition curve shown in t h e diagram. Furthermore, t h e change in vapor composition with change in boiliqg point was determined from t h e slope of the temperature curves just described, and plotted t o make possible t h e estimation of vapor composition of liquids boiling a t pressures other t h a n atmospheric. The boiling point curve given is from t h e d a t a of Noyes and Warfle.l T h e total pressure exerted by any mixture of alcohol and water, a t any given temperature, divided by t h e pressure of pure water a t t h e same temperature, is a ratio which changes b u t little with change in temperature. The value of this ratio is, of course, unity for water, and rises rapidly with increasing alcohol content of t h e liquid t o approximately 2.3 for alcohol itself. The ratio was determined from the pressure measurements of Wrewsky at the temperatures employed b y him, and graphically extrapolated t o the boiling point in exactly t h e same way as t h e vapor composition. The value of this ratio a t t h e boiling point is plotted as a separate curve, and will make i t possible t o estimate temperature-pressure relationships other than atmospheric, as for example in t h e lower part of a rectifying column, 1
J . Am. Chem. SOC., 23 (1901), 154.
Vol.
12,
No. 5
I n any problem in alcohol distillation t h e enrichment is easily realized until t h e constant boiling mixture is approached. The most important part of t h e operation and hence of t h e design is t h a t involved in enrichment above g o per cent alcohol. It is, therefore, desirable t o determine t h e d a t a above this point with t h e greatest possible precision and t o plot i t correspondingly. We have, therefore, appended a separate vapor composition curve for compositions above 85 per cent of alcohol in t h e liquid. I n order t o secure greater accuracy for t h e vapor composition of these liquids rich in alcohol, the d a t a of Wrewsky within this range were replotted in a somewhat different way. Wrewsky’s values for t h e partial pressures of alcohol and of water, obtained by calculation from t h e measured values of t h e total pressure and of t h e vapor composition, were divided in each case by t h e pressure of pure alcohol and of pure water a t t h e temperature of t h e determination. These ratios change b u t slightly with the temperature. For each of t h e three temperatures used b y Wrewsky they were plotted against t h e molal composition of t h e liquid, and smooth curves drawn among t h e individual points. The ratios were read off these curves for each mol per cent of alcohol in t h e liquid, and these ratios plotted against t h e temperature. These last
Xay,
1920
T H E J O L ' K N A L O F 1.YDUSlIU.i L ,1ND E N G I N E E R I N G C H E J I I S T K Y
curves, either straight lines or very Aat, werc extrapolated up t o t h e boiling point, and from the values thus obtained the vapor composition calculated. I t will bc noted t h a t the extrapolation was in no case greater than four degrees, because the boiling points of these rich alcohol mixt.ures are nearly constant. In ordcr t o show the applicability of these curves, let it be assumed t h a t a j o per cent alcohol-water mixture is boiling at a temperature of soo' C. at sonic point in thc lower part of a rectifying column. I t is required t o determine the composition of the vapor and the pressure under which the liquid is boiling. Were the liquid boiling a t atmospheric pressure it would have a vapor composition at 7 7.7 per cent. Vnder these conditions it would boil at 8 2 ' . Sincc it is boiling at ~ o o *its , boiling point has been increased IS' by pressure. From the correction curve it is seen that the vapor composition changes 0.524 per cent per degree. This corresponds t o a correction of 0.9 per cent. Thc correction is positive for a decrease in boiling point and is, therefore. negative for t h e case in question. Hence the vapor composition of the j o per cent alcohol a t 100' is 76.8 pe,r cent. At zooo water excrts one atmosphere pressure. I t is seen from the vapor pressure ratio curve t h a t a ,io per ccnt solution eserts 1.97 times as much, i. c., the pressure at the given. point in the still is 1.97 atmospheres or 1497 mm.
499
adding 0.1 cc. of milk to be tested and incubating, the writer found t h a t the time required t o match the colors, and t o make the necessary changes of tubes t o and from the comparator, was so great that a large number of tubes could not be read each hour by the colorimetric method.
I>$,;.I
To make i t possible to compare a great Iiuii!her ~f unknowns with the standard tubes, the comparator of Hurwitz, Meyer and Ostcnberg' was modified as shown in the accompanying illustrations.
A SIMPLE METHOD FOR THE PREPARATION OF SODIUM AMALGAM IN FLAKES' By Arthur I). Hirschfelder and Merrill C. Hart U~NIYBRSITYos MINNISUTA,MINNBAPOLIS, MINN.
Received Novcmber 28, 1919
In the course of preparation of saligenin by a slight modification of Hutchinson's method made by Xfr. Hurd,? it has been necessary for us t o use a 2 . 7 5 pcr cent sodium amalgam. This amalgam, when poured on t o porcelain plates, forms solid layers, which require a good deal of work and time t o reduce t o a powder in a mortar. We have been able t o prepare a powder of vcry finely flocculent amalgam by pouring the hot liquid amalgam slowly into a battery jar of xylene or kerosene, which is already being rapidly agitated by an elcctric stirrer. The amalgam is broken up b y the currents as fast as it is poured into the liquid and the fine flocculi settle t o the bottom. They are then dried in a current of air on a porcelain plate. When the flocculi are clumpcd they arc readily pulverized by a couple of blows with a pestle. AN IMPROVED COMPARATOR By L. H. Cooledge MLCHIO&NACRICULIVRALC O L L ~ LEAST B ~ ~ ,I.~wairrc, M z C W ~ O A N
Rereived January 12, 1920
While studying the change in hydrogen ion concentrationa of water or o i a solution of broth due to I
From the Ikpartmcnt of Fharmrcology. University of Minnesota,
w i t h the aid of funds xranted hg the United States Interdepartmeiifal Socinl Hygiene Board for Reierrch in the prevention and
