HYDRATES OF TRISODIUM ORTHOPHOSPHATE RUSSELL N. BELL Victor Chemical Works, Chicago Heights, I l l . one third of the molar sodium oxide-phosphorus pentoxide ratio in systems containing only sodium oxide phosphorus pentoxide, and water. It is defined in terms of the above titration as follows:
1 hree hydrates of true trisodium orthophosphate-a hemihydrate, a hexahydrate, and an octahydrate-are confirmed. All higher hydrates, including the so-called dodecahydrate, are complexes containing a monobasic anion. Some monobasic anions form two complexes with trisodium phosphate. The hydrated complexes are divided into two groups, for which type formulas are given. Refractive indexes and melting points are given for the true hydrates and for several of the hydrated complexes. "
3
+
2B A Factor = ___ 3B its value being 1.00 for a ratio of 3Na20to lP206 HYDRATES OF NORIVAL TRISODIUM PHOSPHATE
The following hydrates of trisodium phosphate have been reported in the literature: 1/2H20 (16), 1H2O (11, IQ), 6 H 2 0 (16), 7&0 (8, 11, 19), 8H20 (d), 10H20 ( d l ) , and 12Hz0 (?',8, I S , 16). In this investigation only three of these were found-namely, the hemihydrate, the hexahydrate, and the octahydrate. The reported monohydrate and heptahydrate are believed to have been mixtures, as both the hemihydrate and the hexahydrate were difficult to prepare without serious contamination with the next higher hydrate. Analysis of such mixtures might give results corresponding very closely to those required for the mono- and heptahydrates; unless examined very closely under a microscope their heterogeneous nature would not be suspected. The so-called decahydrate and dodecahydrate are discussed below in connection with the hydrated complexes. NasP04.1/2H20. The hemihydrate was crystallized from a liquor having the theoretical ratio of 3 N a ~ 0to 1P206 (factor of 1.00) at boiling temperature. The crystals were filtered hot and dried t o a constant weight at 112' C., which is above the melting point of the next higher hydrate. Under the microscope the product was found t o be homogeneous. Analytical and crystallographic data are given in Table I. Schroeder, Berk, and Gabriel (19) and Jngerson and Morey (11) reported similar indexes for crystals which they called a monohydrate. No analytical data were given by the first-mentioned authors; the analyses given by the latter do not agree with the assigned formula, for their results indicate the product t o have had a composition approximately that of a dihydrate rather than a monohydrate. This discrepancy was explained as beisg due to adhering mother liquor.
LTHOUGH trisodium phosphate has been known and widely used for a great many years, there is still considerable confusion in the literature regarding the hydrates of this supposedly simple compound. Smith (10) could not prepare pure trisodium phosphate dodecahydrate. Using theoretical proportions of acid and alkali he found the composition to be 2KasPO1.Na2HP04. By using 4% excess alkali he obtained crystals whose composition could be represented by the formula Na20.17.5NaaP04. AIthough more recent workers (12,16) have not accepted this formula, most of them agree that a dodecahyh a t e , NasP04.12H,0, cannot be crystallized from solution. In the work reported here two classes of compounds were studied: true hydrates of trisodium phosphate represented by the formula NasPOJ.XH20, and the hydrated complexes which contain the sodium salt of a monobasic acid. The purpose was twofold: t o identify the hydrates of true trisodium phosphate and to prepare and identify several of the complex hydrates. Three hydrates and ten hydrated complexes of trisodium phosphate have been prepared; sufficient experimental data to establish their identity are presented. METHODS OF IDENTIFICATION
In addition to the usual analytical procedures, microscopical methods were used in the study and identification of these compounds. Refractive indexes were measured by the immersion method, using liquids differing consecutively by 0.002. Unless otherwise indicated, the measured indexes should be considered accurate t o ~ 0 . 0 0 2 . Measurements were made using daylight. The crystallographic data are believed to be sufficiently accurate for routine identification. Because many of these crystals effloresce below their melting points, they were mounted in mineral oil and their melting points were determined under a microscope. The ratio of sodium oxide to phosphorus pentoxide present in these compounds is important in establishing their identity.
This ratio was obtained by titrating the samples with 0.2 N hydrochloric acid. Two end points were taken, the first a t H 9.2 (titration A) and the second at p H 4.5 (titration B). ' h e values for titration B represent the number of milliliters between p H 9.2 and 4.5, not the total titration. Titration B is a measure of the acid required t o convert disodium monohydrogen phosphate t o monosodium dihydrogen phosphate; three times thiR value is the acid equivalent of trisodium phos hate. HowofI? 4.5; conever, only the first two sodiums are replaced at a P aequently, values for A and B should be the same if the substance is a true trisodium phosphate. If A is greater than B, then alkali in excess of the theoretical amount is present. In actual practice the alkalinity is described by a factor which is
TABLE I. ANALYSISOF TRISODIUM PHOSPHATE HYDRATES NaaP04.1/2HzO Found Calod. 40.8 41.0 PzOa Lossat 800° C. 5.36 5.2 Factor 0.994 1.000 Refractive indexes
wl.499 €1.525
NasP04.6H~O Found Calcd. 26.0 26.1 41.5 39.7 0.995 1.000
NaaPOc8HzO Calod 23.3 23.0 47.0 46.8 Found 1.004
1.0011
P 1.473 ~
_
Na3P04.6H20. The hexahydrate was prepared by crystallization from a liquor above 86" C. Microscopic examination revealed the presence of a small amount of octahydrate. Analytical data and optical properties are also summarized in Table I. The crystals of this hydrate (Figure 1) do not resemble the other hydrates nor the hydrated complexes of trisodium phosphate, Ingerson and Morey ( 1 1 ) gave similar refractive indexes for their 2901
_
2902
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
F i g u r e 1. T r i s o d i u m Phosphate H e x a h y d r a t e in Transmitted L i g h t (25X)
so-called heptahydrate, but did not verify the composition of their product by analysis. NaaP04.8Hz0. The highest hydrate of true trisodium phosphate is the octahydrate. This was prepared by a batch process. A hot liquor containing the proper ratio of sodium oxide to phosphorus pentoxide and only a slight excess of water, over that necessary to form the octahydrate, was placed in a mixer and agitated until complete crystallization had taken place. Analysis, refractive indexes, and melting point of one such batch are given in Table I. Under the microscope these crystals resemble those of the hydroxide complex in general appearance. They can be distinguished readily from the latter by their refractive indexes or melting point. The octahydrate usually exhibits higher polarization colors and will show extinction angles up to 22 ', depending on the orientation of the crystal. Figures 2' and 3 are photomicrographs showing the same crystals of trisodium phosphate octahydrate in transmitted light and between crossed Kicols. The crystal parallel to the horizontal cross hair is not a t extinction, whereas the one inclined 23 from the same cross hair is almost completely extinct. The hydroxide complex, the familiar T.S.P. of commerce, exhibits only parallel extinction. Some difficulty was encountered in determining the optical properties of the octahydrate because of a strong tendency toward an apparent vertical axis twinning. HYDRATED TRISODIUM PHOSPHATE COMPLEXES
The trisodium phosphate compounds containing more than 8Hz0 are not simple hydrates but hydrated complexes which always contain the sodium salt of a monobasic acid or sodium hydroxide. 3-0complexes could be prepared with the salts of polybasic acids such as sodium sulfate, sodium carbonate, disodium hydrogen phosphate, or sodium tetraborate. These complexes are of two types. The first, exemplified by the fluorine complex, has the formula nIia3POa.hTaY.XHzO where n = 1 or 2, Y is a monobasic anion, and X = 18 or 19. Two complexes of this type have been prepared. The second type of complex, of which the commercial T.S.P. is the best known example, has the formula n(Na3P04.XH20)NaYwhere n = 4 to 7 , X = 11 or 12, and I' is a monovalent anion. Several complexes of this type have been prepared. The crystal properties of the members of the second group are very much alike, all of them being trigonal, uniaxial negative with refractive indexes which are very similar. They differ but slightly in their melting points. Because they are efflorescent, it is difficult t o distinguish between them by this means. nNaaP04.NaY.XH20 Type Complex. Although several complexes of sodium fluoride and trisodium phosphate have been reported (3, 7, 18),probably only one exists. Mason and Ash-
Vol. 41, No. 12
craft (14) found only 2SaaPO4.XaF.l9H20, which was identified sufficiently well and was not investigated further by the author. Another complex of this type contains sodium metaborate and has the formula Na3P04.XaBO2.18H20 (9). This compound was prepared by crystallization from a liquor having a factor of 1.00 and containing a slight excess of sodium metaborate. Analyses, melting point, and optical properties of this compound are given in Table 11. The two members of this group have entirely different crystallographic characteristics, but neither resembles the crystals 01 the second type of complex. n(NasP0,.XH20)NaY Type Complex. Commercial crystalline trisodium phosphate is a complex containing excess sodium hydroxide. This, as well as several other complexes of this type, is claimed in various United States patents. -411 but one of these have been prepared and studied. The presumed borax complex (4) could not be prepared by either of the methods used in this investigation.
PATENTED TRISODIUM PHOSPHATE COMPLEXES S(NaaPOa.12H20)2NaOH NasPOa.sodium borate (no foi muis) 5(NasP04.12H~O) .NaCi 4(NarPOa.l1HzO)NaN03 4(~;asP04.11H~O)NaOCI K\;asPOd.NaMnOa(no formula) NaaPOa.NaBO~.lS€I~O PREPARATION.These complexes can be prepared by either of two processes. The purest products are obtained by crystallizing from a liquor having the proper sodium oxide-phosphorus pentoxide ratio and containing an excess of the added salt,. The second method involves crystallization in a batch-type mixer where the starting liquor is more highly concentrated and the entire solution is crystallized, leaving no mother liquor. In the latt'er met'hod it is necessary that the sodium oxide-phosphorus pentoxide ratio does not exceed 3 to 1, that the correct amount of the complex forming salt be added, and that only a slight excess of water over bhat necessary for crystal formation be present. Deviation from these proportions will result in the formation of a mixture rather than a homogeneous product. A slight excess of water will merely require more drying time; insufficient water will give some trisodium phosphate oct ahydrate, with the result that a corresponding amount of the complex-forming salt will remain uncombined in the mixture. A liquor deficient in sodium oxide mill produce disodium hydrogen phosphate (usually the dihydrate). A liquor low in phosphorus pentoxide will give a mixture containing some of the hydroxide complex, which forms preferentially, and crystals of the added salt. If an insufficient amount of the complex-forming salt is used trisodium phosphate octahydrate will be produced. Any excess of the complex-forming salt will be found as such in the crystallized product. If the added salt does not form a complex, rn was the case with the tetraborate, microscopic examination will reveal the product to be trisodium phosphate octahydrate contaminated with the addend. UJith the exception of the hypochlorite complex, the analyses shown in Table I1 were made on products crystallized from solution rather than prepared by the batch procedure, although most of them ha,ve been prepared by both methods. Hydroxide Complexes. The most common hydrate of trisodium phosphate, T.S.P. of commerce, is the complex containing excess sodium hydroxide (12, 16, do). Smith ($0)found the composition t o correspond to the formula 17.5NaaPO4.Naz0, while Kobe and Leipper (12) obtained a compound having the formula 5NaaP04.NaOH. Menzel and Von Sahr (16) reported a series of solid solutions having varying amounts of excess sodium hydroxide but could find no difference in x-ray patterns among members of the series. Quimby (17) assigned the formula NasPO4.(12 -X)H20.XNaOH to the product and suggested that
INDUSTRIAL AND ENGINEERING CHEMISTRY
December 1949
2903
TRISODIUM PHOSPHATE COMPLEXES TABLE 11. HYDRATED Analysis
Yo Loss a t 800° C.
% Pros Complex
Found
Calcd.
Found
Calcd.
crys-
70N a y Found
Calcd.
tal
2.1 1.5 4.55 2.6 7.3 5.3 4.9 3.1 5.5
u
OI,tic Sign
Refractive Indexes o
6
hr,p,a,
c.
Type n(NaaPO4.XHzO)Na Y
d
5 NaaPO4.12 H20) NaO 7tNaaPOa. 12Hz0)NaOH 4 ( NasP04.11HzO) NaNOz 7(NasPO.i.llHzO)NaNOz 5(NaaPO:.llHzO)NaMnO4 7(NaaP04.11HzO)NaMn04 4(Na~PO4.11HzO)NaOCl 5(NasPO:.llHzO)NaCl 4(NasP0~11HzO)NaNOs
18.6 18.9 18.7 18.6 18.25 18.3 18.2 18.5 18.9
18.3 18.4 18.7 19.0 18.2 18.5 18.7 19.0 18.5
55.8 55.9 54.8 54.9 51.4 53.0 51.9 55.1 54.5
55.6 56.0 52.2b 53.2b 50.7b 51.8b 52.0b 53. Ob 61.6b
2.2 1.3 4.4
2.6 7.0 5.5 4 2 3.1
5.1
..
U
..
+ +
,.
, .
1.447
...
1.447
...
...
a b
12.8 20.0
58.4 Not detd.
58.5 48.0
13.0 Not detd.
11.9 5.9
....
+
Too highly colored
U U
$ +
1.450 1.447 1.444
B
-
1.446 1.451 1.463 1.452
U U
c2
13.0 Not detd.
74 70 72
. I .
1.442
Type nNaaPO1.Na Y .XHzO N~aPO:.NaBOz.l8HzO 2NasPOh.NaF. 19HzO
1.452
I
1.455 1.453 1.450
o
: E:
62 61 60
r 68
Not true melting points but rather transition points t o N a s P 0 4 H z 0 . Calculated loss does not include loss from addition salt.
CONTENT OF HYDROXIDE TABLE 111. SODIUMHYDROXIDE COMPLEXES Liquor 0.94 0.96 0.98 1.00
1.05 1.10 1.17 1.25
-
Factor Crystals 1.04 1.04 1.06 1.07 1.07 1.07 1.07 1.07
Filtrate 0.94 0.93 0.94 0.99 0.99 1.12 1.40 1.60
Factor of 1.04 = NaeO/PzO6 ratio of 3.12:l. Factor of 1.07 NazO/PzOs ratio of 3.21:l.
the excess sodium hydroxide replaces some of the water of crystallization. The question of variability of the sodium hydroxide content of such products was investigated by preparing solutions of sodium phosphate having amounts of alkali both greater and less than the theoretical quantity required for trisodium phosphate. These solutions were not highly concentrated and were allowed t o crystallize slowly. The crystals were filtered off and washed well with ice water. The starting liquor, the crystal product, and the resulting mother liquor (not including the wash liquors) were checked for sodium oxide-phosphorus pentoxide ratio by the titration procedure described above. The results are given in Table 111. With one exception all the crystalline products had factors of 1.07 or 1.04, corresponding to sodium oxide-phosphorus pentox-
Figure 2.
Trisodium Phosphate Octahydrate in Transmitted Light (75 X)
ide ratios of 3.21 t o 1 or 3.12 t o 1. These results indicate t h a t two hydroxide complexes form having definite formulas rather than a series of solid solutions of varying sodium oxide-phosphorus pentoxide ratios. The product having a ratio of 1.06 is believed to be a mixture of these two complexes. This opinion is based on an examination of the results shown in Table 111. Crystals having a factor of 1.07 crystallized from liquors with factors as low as 0.98, but not from liquors having a factor of 0.96 or lower. As crystals form in a low factor liquor, below 1.04, the liquor factor drops. I n the case in question the starting liquor had a factor of 0.98 but the resulting mother liquor factor was only 0.94, from which only 1.04 factor crystals should crystallize. From such a liquor crystals having a composition represented by the factor 1.07 would be produced until the solution had become so depleted with respect t o its sodium oxide content t h a t only crystals with a 1.04 factor could form; t h e resulting product would then consist of a mixture of the two hydroxide complexes. Such mixtures were probably obtained by previous workers, from which they concluded that a series of solid solutions containing varying excesses of sodium hydroxide could form. If the starting liquor is highly concentrated, such a mixture is more likely t o form, as the liquor factor would vary over a wider range owing to the removal of a large amount of alkali by the crystals. Removal of a large quantity of crystals from a solution might reduce the li uor factor from 1.02 t o t h e point where some 1.04 factor crystays would form. I n this way mixtures would be produced from all solutions with factors of 1.02 down to 0.96. For this reason, in preparing the series shown in Table I11 t h e starting liquor was purposely made dilute enough so t h a t only a small amount of crystals would be produced and the factor of the
Figure 3.
Trisodium Phosphate Octahydrate between Crossed Nicols (75 X )
INDUSTRIAL AND ENGINEERING CHEMISTRY
2904
crystallizing liquor would not vary too greatly. The crystals produced were large enough t o make separation and washing easy. Analysis of the high factor crystals indicates t h a t either the formula 9(Sa3P04.12HzO)2NaOHgiven by Adler (1) or 5(NaaP O ~ . I ~ H Z O ) X ~reported OK by Kobe and Leipper (1%)could be correct. For the sake of simplicity the latter is preferred. The torniula 7(NajP01.12€IzO)XaOH was calculated from an analysis of the low factor crystals. Complexes other than the hydroxide complex mere also prepared with a 7 to 1 ratio of trisodium phosphate to added salt. The analyses of the hydroxide complexes and related compounds are given in Table 11, and are compared with theoretical values required for the formulas assigned t o them. Some of the physical and optical properties are also included t o emphasize the similarity in crystal structure of the complexes of this type. Preferential Order of Formulation of Complexes Using the Batch Process. Crystallization of these complexes from a liquor is less likely to produce a heterogeneous product, for the excess liquor tends to minimize the effect of slight variations in starting composition; howevrr, use of the batch procedure in preparing these cornpiexes led t o some interesting observations. If two salts capable of forming complexes mere both present in sufficient quantities one complex would form in preference t o the other, rather than a mixture of both. For example, if sufficient sodium hydroxide is present the hydroxide complex forms in preference to any of the others of the type n ( S a 3 P 0 4 . X H 2 0 ) S a Y In order to produce any complex other than the hydroxide, no more than the calculated amount of sodium hydroxide t o produce trisodium phosphate should be present. By studying pairs in this series the following order of formation was found t o prevail:
Complex-Forming Salt
NraOH KaMnOp KaOCi
SaCl
SaNOa
M.P.,
0
rials could then either be mixtures of two complexes or, as was suspected from the similarity in crystal structures of the members of this series, could represent solid solutions. The color of the permanganate complex made it possible t o establish the isomorphism of these compounds. \I. hen 7070 of the calculated amount of .;odium chloride or sodium hypochlorite was added to a batch liquor containing 3070 of the calculated amount of sodium permanganate, all of the complex ciystals were found t o be colored when examined under the microscope. S o sodium chloride crystals were found in the first case, while the hypochlorite was found in stable combination in the second. That the coloi was not due to surface dyeing was demonstrated by the fact that uncolored crystals of trisodium phosphate octahydrate formed in batches of low water content, whereas uncolored crystals of di sodium hydrogen phosphate dihydrate were identified in batchch deficient in sodium oxide. \Then prepared by cryotallization from a liquor con taining both permanganate and chloride, all the crystals were colored and no sodium chloride crystals could be found by microscopic examination; yet analysis of the product showed 1% of sodium chloride to be present. These complexes appear t o form an isomorphous series, as the permanganate content could bc varied over a wide range. Further evidence of their isomorphous nature was obtained in trying to establish the formula of the nitrate and permanganate compounds. Crystals obtained from solutions having a factor of 1.00 and coiitdining varying amounts of the complex-forming salt were analyzed for the added salt and for excess sodium oxide. Large excesses of the salt mere necessary t o produce a crystal having no exces? sodium oxide with the nitrate, nitrite, and permanganate complexe.;
I
c.
74 d. 70 62 61
60
t
:I ',02
g 111 this series, if a sufficient quantity of one salt was present to Form the complex, any salt below it w'aa found uncombined in the product. Only because this was true was i t possible t o produce the hypochlorite complex by the batch process. I n preparing a sodium hypochlorite liquor an equimolar amount of sodium chloride is also present. If the hypochlorite complex did not show preferential formation, one of three possible products would have been produced. The chloride complex might have been formed, leaving the unstable sodium hypochlorite free in the product, or a mixture or isomorphous system of the complexes might have been produced. I n any case, either half or all of the hypochlorite would have been lost. When the product was examined under the microscope three varieties of crystals were found to be present and identified by refractive indexes: long trigonal crystals of the hypochlorite complex ; small orthorhombic crystals of the disodium hydrogen phosphate dihydrate (due t o a slight deficiency in sodium oxide); and small isometric crystals of sodium chloride. Usually a few crystals of trisodium phosphate octahydrate were also present. This order of preferential formation of complexes using the batch process corresponds with the decreasing order of melting points of these compounds. The higher melting complexes form in preference t o those having a lower melting point. The sodium nitrite complex was not included in the above tests b u t from its melting point (72' C.) should form in preference t o all but the hydroxide complex. Isomorphism. Analysis of products crystallized from a solution containing two complex-forming salts showed both salts to be prewnt although usuallv not in q u a l proportions. Such mate-
Vol. 41, No. 12
1.00
U
'98
1
U' I 1
Figure 4.
2
W
3
4
I
5
I
6
I
'I
NaMnO4
Trisodium Phosphate-Sodium Complexes
Permanganate
Evidence t h a t two of these salts form two complexes each was also found. This is shown in Figure 4, where the permanganate content is plotted against the factor for products, cryst,allized from liquors, which had a factor of 1.00 and contained varying amounbs of sodium permanganate. Products containing small amounts of permanganate have factors above 1.00, indicating an isomorphous system of permanganate and hydroxide complexes. As the permanganate content increases, the factor drops. The point where the factor reaches 1.00 would, therefore, be a true permanganate complex. This point, as shown on Figure 4, is at 5.3y0of sodium permanganate, which corresponds to a product having the formula 7(9a.?P04,11HzO)Pu'aMnOl. While the factor remained constant above this point, t'he permanganate content increased until the product approached the formula of the This procedure was other complex, 5(NajP0~.llHzO)Na?uIn0~. also used t o demonstrate the existence of a nitrite complex having a 7 t o 1ratio of trisodium phosphate t o added salt. No nitrate or chloride complex having this ratio was found.
December 1949
INDUSTRIAL AND ENGINEERING CHEMISTRY SUMMARY
9
*
2908
LITERATURE CITED
Normal trisodium phosphate forms three hydrates-a hemihydrate, a hexahydrate, and a n octahydrate-which can be identified by their optical properties and melting points. All higher hydrates were found to be complex salts. Trisodium phosphate forms hydrated complexes with the sodium salts of monovalent ions. These complexes are of two types. The f i s t is represented by the formula nNaaP01.NaY.XH20where n = I or 2, Y is a monovalent anion, and X = 18 or 19. The best known member of this type is the fluorine complex, ZNaaPOd.NaF.19HzO. The type formula for the second group is n(NasPOr.XHzO)NaYwhere n = 4 to 7 , X = 11 or 12, and Y is a monovalent anion. Two complexes are formed by some members of this series, both of which fall within the limits of the type formula. The crystal structure and optical properties of the complexes of the second type are very similar, all of them being trigonal and optically positive, and having similar refractive indexes. Some of the members of this group form an isomorphous series. The best known member of the second type is the hydroxide complex with the formula 5(Na3POa.l2HzO)NaOH, representing the common form of commercial trisodium phosphate. ACKNOWLEDGMENT
The author wishes to thank Howard Adler and W. H. Woodstock for many helpful suggestions, L. E’. Audrieth for assistance in preparing the paper for publication, and A. R. Wreath for some of the analyses reported.
Adler, H., U. S. Patent 2,050,249 (1936). Baker, Harry, J . Chem. SOC.Trans.,47, 353-61 (1895). Baumgarten, A., “Uber das Vorkommen des Vanadiums in dern Aetanatron des Handels und ein neues vanadianhaltiges Natriumfluorphosphat,” dissertation, GGttingen, 1865. Booth, C. F., Gerber, A. B., and Logue, P., U. S. Patent 1,769. 152 (1930).
Zbid., 1,688,112 (1928). Bowman, F. C., Zbid., 1,890,453 (1932). Briegleb, H., Ann., 97, 9 5 (1855). D’Ans, J., and Schreiner, O., 2. physik. Chem., 75, 96 107 (1911).
Gale, W. A., and Ritchie, C. F., U. S. Patent 1,895,620 (1933, Hull, H. H., Ibid., 2,324,302 (1943). Ingerson, E., and Morey, G. W., Am. Mineral., 28, 448-56 (1943).
Kobe, K. A., and Leipper, A., IND.ENQ.CHEM.,32, 198-206 (1940).
Korf, D. M., and Balyasnaya, A. M., J . A p p l i e d Chem. (U.S
S.R.), 14, 475-7
(1941).
Mason, C.W., and Ashcraft, E. B., IND. ENQ.CEIEM., 31,768--71 (1939).
Mathias, L. D., U. S. Patent 1,555,474 (1925). Menzel, H., and Von Sahr, E., 2. EEektrochem., 43, 104 19 (1937).
Quimby, 0. T., Chem. Revs.,40, 141-79 (1947). Rammelsberg, C. F., Monatsh. Akad. Bull., 1880, 777. Schroeder, W. G., Berk, A. A., and Gabriel, A., J . Am. C’hena SOC.,59, 1783-95 (1937).
Smith, J. H., J. SOC. Chem. Znd., 36, 420-4 (1917). Westbrook, L. R.,U. S. Patent, 1,711,707 (1929). R E C E I V February ~D 17, 1949. Presented before the Division of Physioal and Inorganic Chemistry at the 112th Meeting of the AMERICAN CHEMICAL SoCIQTY, New York, N. Y.
Vapor-Liquid Equilibria Measured by a Gillespie Still ETHYL ALCOHOL-WATER SYSTEM ROBERT M. RIEDERI AND A. RALPH THOMPSON University of Pennsylvania, Philadelphia, Pa. Vapor-liquid equilibrium data at 760-mm. pressure are presented for ethyl alcohol-water as determined in a Gillespie still. These data, the first to be published as a test of this still, show slightly less separation at low alcohol concentrations than some values published previously. Boiling point curves and activity coefficient curves show good agreement with those of Jones, Schoenborn, and Colhurn (5). A slight modification of the still is suggested.
I (4)
N CARRYING out another investigation involving ternary systems containing an inorganic salt, the use of a Gillespie was considered. I n order t o determine the reliability still of this new type of vapor-liquid equilibrium still, it was decided to check the published data for ethyl alcohol-water solutions a t atmospheric pressure. This system was chosen because it had been so thoroughly investigated in the past and because its analysis can be made very simply and accurately by density measurements. In any equilibrium still, the major possible sources of error are: 1
Present addrens, Eastern Regional >ResearohLaboratory, Philadelphia
18. Pa.
Refluxing of the vapors, thereby increasing the concentration of the low-boiling component in the vapor. Entrainment of liquid into the vapor stream leaving the boiler, thus decreasing the concentration of the more volatile component in the vapor. Inadequate or slow mixing of the returning condensate with the liquid in the still pot, causing the lower boiling condensate to flash as soon as it meets the hot liquid. FEATURES O F THE GILLESPIE STILL
The still used in these experiments was exactly as constructed by Gillespie (4). It was built entirely of Pyrex glass and, since no lagging of the still pot was found t o be necessary t o ensure heat for boiling, the liquid levels could be observed easily during operation. Two heating coils were used at the still pot, the internal one being 15 inches of 28-gage platinum wire and the external one Nichrome. Each of these coils was controlled by a 5-ampere Variac with a 16-ohm resistance in series with the coil to cut down the heat input. The possibility of refluxing in this still is extremely slight because the vapor and liquid are not allowed to separate in the boiler but are kept in intimate contact as they pass up the Cottrell pump t o a vapor-jacketed disengagement chamber
