November, 1934
INDUSTRIAL AND ENGINEERING CHEMISTRY
EFFECTOF COOLING RATE. The rate of cooling has no appreciable influence on the inoculating or mechanical effects, but the temperature decrease may be too fast for the nucleus formation to keep up, and higher cooling rates would result in wider gaps. Figure 4 shows such an effect. EFFECTOF STIRRING SPEED. The obvious effect of increasing stirring speed is to increase the mechanical effect and therefore to decrease the gap. Such an effect is shown in Figure 5 . The fact that beyond 200 r. p. m. the speed of stirring has no effect is consistent with the known fact ( I ) that a stirrer reaches a limit in effectiveness as the speed is increased. There is probably a change in inoculation effect with stirrer speed, especially a t the lower speeds, where the seed crystals are not dispersed through the solution as uniformly as a t higher speeds. The fact that the 28EFFECT OF SIZEOF SEEDCRY~TALS. mesh-per-inch (11-mesh-per-cm.) seeds gave wider gaps than did larger or smaller crystals (Figure 3) is peculiar. KO simple explanation of this effect is available.
1207
LITERATURE CITED (1) Badger, W. L., and McCabe, W. L., "Elements of Chemical Engineering," pp. 481-2, McGraw-Hill Book Co., New York, 1931. (2) Coppet, L. C. de, Ann. chim. phys., 10,457 (1911). (3) Fouquet, G., Compt. rend., 150, 280 (1910). (4) Hartley, H., Jones, B. M., and Hutchinson, G. A,, J . Chem. Soc., 93, 825 (1908). (5) Hartley, H., and Thomas, X. G., Ibid., 89, 1013 (1906). (6) Isaac, F., Ibid., 93, 384 (1908). (7) Jones, B. M., Ibid., 93, 1739 (1908); 95, 1672 (1909). ( 8 ) Jones, B. M., and Shah, P. G., Ibid., 103, 1043 (1913). (9) Miers, H. A., J. Inst. Metals, 37, 331 (1927). (10) Miers, H . A., and Isaac, F., Proc. Rou. SOC. (London), 798, 322 (1907); 82-4, 184 (1910); J . Cheni. SOC.,89. 413 (1906); 93, 927 (1908). (11) Ostwald, W., 2. physib. Chem., 22, 289 (1897). (12) Young, S. W., J. -4m. Chem. SOC.,33, 148 (1911j. (13) Young, S. W., and Van Sicklen, TV. F., J. A m . Chenr. Soc., 35, 1067 (1913).
RECEIVED July
2, 1934. Extracted from a thesis submitted by Hsii Huai Ting in partial fulfilment of the requirements for t h e degree of doctor of philosophy, University of Michigan.
Solubility of Magnesium Sulfate Heptahydrate Hsu HUAI TING~ AND WARRENL. MCCABE,University of Michigan, Ann Arbor, Mich. H a u e r (2020), Van d e r H e i d e URING experiments on N e w data on the solubility of magnesium sul( I o ) , G u t h r i e (9)s f i t a d (61, the c r y s t a l l i z a t i o n of fate hepkhydrate in the temperature range 290 magnesium sulfate hepand Weston (21). The results to 45" C. are reported. The data are consistent of t h e s e investigations a r e tahydrate, trouble was experienced in o b t a i n i n g the yields with recent accurate data at 25' and indicate plotted as individual points in called for by the solubility of significant errors in older data in the range 2" Figure 1. The second group of solubilithis material at the end temperato 40" C . ture of the process. Crystalline ties contains those determined crops from 50 to 100 per cent larger than theoretical were by Basch (11, Grunewald ( 8 ) , Van Klooster ( I @ , Blasdale obtained. The difficulty was traced to the solubility data ( Z ) , Takegami ( l 7 ) , Jackman and Brown ( I I ) , and Schnellwhich were taken from the literature. It was found that the back and Rosin (16). These data were grouped together in data available on the solubility of magnesium sulfate hepta- the last seven lines of Table I. The determinations are in hydrate were, with the exception of those at 25" C., old and satisfactory agreement. The average of those of Grunewald, inconsistent with themselves and with the results of recent Van Klooster, Blasdale, Takegami, and Schnellback and determinations carried out a t 25" C. The discrepancies were Rosin is 26.66 parts magnesium sulfate per 100 parts water, easily apparent when the data were expressed in parts of This result is plotted as point A in Figure 1, which is a comanhydrous magnesium sulfate per 100 parts of solution, and posite point of good accuracy. It will be noted that most were greatly magnified when the solubilities were expressed, of the older solubilities are definitely high in comparison with for the purpose of crystallization calculations, in parts of hy- point A. The dotted line of Figure 1 shows the solubility curve recdrated salt per 100 parts of free water, To reduce the uncertainity in such calculations, the solubility of magnesium ommended by Bronsted in the International Critical Tables sulfate pentahydrate was determined experimentally over a (3). It gives considerable weight to the 25' C. data, but it passes somewhat above point A of Figure 1. temperature range of 30" to 45" C.
D
EXISTINGDATA Magnesium sulfate heptahydrate is stable over a temperature range of 1.8" (6) to 48.4' C. (4). The available solubility data in this temperature range are shown in I- The data fa11 into two groups: The first group consists mostly of older data obtained at various temperatures; the second group consists of recent data deExcept for one Point from Weston (21) termined a t 25" a t 30' c. there are no recent data a t any temperature other than 25" C. In the first group are points determined by Gay Lussac ( 7 ) , Loewe1 ( I % , Tobler (18), Schiff (15), Mulder (141, Von
*
Present address, Peiyang Engineering College, Tientsin, China.
c.
EXPERIMENTAL PROCEDURE Although constructed for another purpose, a glass batch crystallizer was used to determine new solubility data. The apparatus is described elsewhere ( 1 3 ) . spite of the fact that the equipment differed from the usual solubility apparatus, it served its purpose well. The efficient agitation insured rapid approach to equilibrium, and the equilibriurn could be approached from either the supersaturated or the undersaturated direction. In those experiments where the approach was from supersaturation, a warm concentrated solution was cooled in the crystallizer and inoculated with seed crystals. After cooling to a definite temperature a t which the solubility was desired,
INDUSTRIAL AND ENGINEERING CHEMISTRY
1208
Vol. 26, No. 11 I
34,
the temperature was held constant for 2 to 3 hours. At intervals samples were withdrawn and their sulfate contents determined gravimetrically as barium sulfate. It was found that equilibrium was attained within an hour. When the solubility a t one temperature was obtained, the solution was cooled to a lower temperature and the determination repeated. I n t h o s e experiments where equilibrium w a s approached from undersaturation, the undersaturated solution was a g i t a t e d w i t h s m a l l c r y s t a l s of c. P. magnesium sulfate heptahydrate a t constant temperature until a constant concentration was reached. When one determination was complete, the solution was heated to the next temperature, more of the salt added, and saturation again reached. In sampling the solution, the stirring was stopped, the crystals were allowed to settle, and about 2 cc. of solution were sucked into a short length of 7-mm. glass tubing. The end of the tube was constricted to a tip 3 mm. in diameter. d short piece of 4-mm. glass tubing was attached to the tip by means of rubber tubing. The 4-mm. tube contained a cotton plug to act as a filter and to prevent any small crystals from being carried away in the sample. The results are given in Table 11. The final results, obtained by averaging arithmetically all solubilities obtained a t a given temperature, are shown in the last column of Table I1 and are plotted in Figure 1. Inspec-
j
..-" -
10
20
30
40
50
TEMPERATURE * C .
OF MAGNESIUM SULFATE HEPTAHYDRATE FIGURE 1. SOLUBILITY
tion of Figure 1 shows that the new data are consistent with TABLEI. EXISTING DATAON SOLUBILITY OF MAGNESIUM point A , and that the solubility curve over the range 25" to SULFATE HEPTAHYDR.4TE 48' C., as shown by the solid line of Figure 1, is well defined. SOL. of It was found ( I S ) that the new solubility data predicted M 904 PEIR 100 yields from the crystallization of magnesium sulfate heptaTBIMP. +ART, sOLN. OBU~RVEIR * c. Parts hydrate that were within a few per cent of those obtained in 24.68 14.6 Gay Lussac 1819) actual crystallization, 31.06 Gay Lussac {lSlQ) 39.9 23.61 26.25 27.0 32.0 25.4 28.2 29.0 31.3 25.67 26.38 25 30 33 20.9 22.5 26.0 29.03 26.8 26.87 26.76 26.68 26.68 26.30 26.65
10 20 25 40 23 25 30 40 18 20 15 31 48 2 7 23 30 25 25 25 25 25 25 25
TABLE 11.
Loewel 1855)
Loewel $1855)
LITERATURE CITED
(1) Basch, Dissertation, Berlin, 1901 : Landolt-Bornstein, Physik. alisch-chemiache Tabellen, 5th ed.? Vol. I, p. 666, Julius Springer, Berlin, 1923. (2) Blasdale, IND. ENG.CHEM.,12, 164 (1920). (3) Bronsted, International Critical Tables, Vol. IV, p. 225, McGraw-Hill Book Co., New York, 1926. (4) Carpenter and Jette, J . Am. Chem. SOC.,45, 578 (1923). Etard (1894) (5) Cottrell, in van't Hoff, Meyerhoffer, and Smith, Sitrber. k . preuss. Akad. Wiss., 1901, 1035. (6) htard, -4nn. chim. phys., [71 2, 503 (1594). (7) Gay Lussac, Ibid., [21 11, 296 (1519). (8) Grunewald, Dissertation, Erlangen, 1913. (9) Guthrie, Phil. Mag., [5] 1, 366 (1876). (10) Heide, van der, 2. physik. Chem., 12, 415 (1893). (11) Jaokman,and Brown, J . Chem. Soc., 121, 694 (1922). (12) Loewel, Ann. chim. phys., [3]43,405 (1555). (13) McCabe and Ting, IND. ENQ.CHEM.,26, 1201 (1934). (14) Mulder, "Bijdragon tot de geschiedenia van het scheikundig OBSERVEDSOLUBILITIES OF MAGNESIUM SULFATE gebonden water," p. 51, Rotterdam, 1864; Landolt-Born-
HEPTAHYDRATE AT 30'
TO
45' C.
-8OLUBITITY. PARTS MgSOi P B R 100 P A R T 5 SOLUTION-FROM SUPER8ATVRATION-FROM UNDmRSATURhTION-
No. of
observs-
TXMP. tionn O
c.
29.89 34.72 35.92 39.97 40.9s 45.01
Max.
Min.
28.06 29.32 29.7i 30.79 31.00 32.31
27.97 29.23 29.55 30.71 30.95 32.26
No. of observa-
tiona
Max.
Min.
Av.
..33
28.04
27.98
291k4
...
29:03
3
32:is
32:il
28.02 29.26 29.63 30.76 30.97 32.26
.. ..
...
stein, Physikalisch-chemische Tabellen, 5th ed., Vol. I, p. 666,Julius Springer, Berlin, 1923. (15) Schiff, Ann., 109, 325 (1559). (16) Schnellback and Rosin, J . Am. Pharm. Assoc., 18,762 (1929). (17) Takegami, Mem. Coll. Sci. Kudo I m p . Univ., 4,317 (1921). (18) Tobler, ilnn., 95, 193 (1855). (19) Van Klooster, J . Phys. Chem., 21, 513 (1917). (20) Von Hauer, Sitzber. A k a d . Wiss. Wien, 53, 221 (1566). 121, 1223 (1922). (21) Weston, J . Chem. SOC., RECBIVED September 4, 1934.
