T H E SOLUBILITY OF LIME IN AQUEOUS SOLUTIONS O F SUGAR AND OF GLYCEROL' BY F. K . CAMERON AND H. E. PATTEN
Introduction In a previous publication from this laboratory' a r h m 6 was given of the extant data upon the solubility of lime in various solutions. It was concluded that when lime is brought into contact with sugar solutions, the ratio of lime to sugar in the solid varies continuously with the composition of the solution ; and consequently the solid compound resulting when lime is added in excess to a sugar solution is one of a series of solid solutions. The data on record, however, possess the common defect that the quantities of sugar remaining in solution after contact with the lime were not determined. The original sugar concentrations of the solution were known, and the quantities of lime dissolved by it were determined; but the sugar in the resulting solution not being determined, there is a possibility that some of the sugar may have been precipitated in the solid (lime) phase. While the existence of a compound of lime with sugar is known, and this fact would indicate the strong probability that some sugar at least would be withdrawn from a sugar solution in contact with excess of lime, yet it is to be remembered that water breaks down the crystalline lime-sugar compound. The System, Lime-Sugar-Water at 25" Cane sugar solutions varying from 0.5-40 percent were prepared, and slaked lime added to each in slight excess. The physical properties of the system, lime-sugar-water, are such as t o render difficult the attainment of equilibrium conditions. The lime compacts into balls and cakes and these Published by permission of the Secretary of Agriculture. * T h e action of water and aqueous solutions upon soil carbonates. F. K. Cameron and J. M. Bell, Bull. No. 49, Bureau of Soils, U. S. Dept. of Agriculture (1907).
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F . K . Cameron and H.E. Patten
resist disintegration into a flocculent sediment, even under months of shaking in a thermostat. Consequently to ensure the formation of a solid phase in final equilibrium with the solution, it was found desirable to saturate the sugar solution with lime at a low temperature-about o o C-where it is more soluble, and then pour off the supernatant solution. This saturated liquid was then allowed to warm up to 25' with constant agitation in the thermostat. The solid phase which deposited from solution was finely dvided and showed no tendency to form aggregates. The sugar solutions are of course very viscous a t room temperature. The viscQsity decreases rapidly with rise in temperature, but the solubility of lime in these solutions also decreases. If the stiff solution be heated in order to stir it, then fine particles of solid phase appear throughout the liquid, and if these be allowed to settle while the solution is hot, has again then on cooling, the supernatant liquid-which become stiff-regains its higher solvent power for lime. It is well nigh impossible to bring this stiff liquid into intimate contact with a sufficient surface of solid phase to ensure equilibrium. Consequently it was found impracticable to study the lime-water-sugar system a t high concentrations of sugar and lime. The fact that considerable lime will dissolve in these stiff syrups may of course be shown and is of interest in itself, but the main object of the present work is to determine the character of the solid phase under equilibrium conditions, and the stiffer sugar solutions are not adapted t o this purpose. The complete dry combustion of the solution was made in oxygen supplemented by copper oxide, the carbon of the sugar being weighed as carbon dioxide; and the colvent wate plus the constitutional water of the sugar were weighed together as water. Given the weight of carbon dioxide, the weight of constitutional water in the sugar can be computed, and deducting this leaves the water originally added to make UP the solution. The lime in solution was determined separately b y evaporating the solution in platinum, burning off the sugar
Solubility of Lime in Sugar Solutions
69
and igniting before the blast lamp. In the case of a solid phase rich in lime, the combustion was carried out a t high temperature to decompose the calcium carbonate formed. Several combustions at lower temperature left a residue in the combustion boat rich in carbonate, but b y using a higher temperature, not a trace of carbonate remained. For the solid phase the percentage of lime is so high and the carbon dioxide and water determinations so accurate, that the lime was in some cases taken by difference; but the solutions were analyzed for lime directly in every case. The solid phase obtained was in no case crystalline. Under the microscope it appeared as 'fine globular granules. consequently a sharp separation from the mother liquor was not feasible. To obviate this difficulty the solutions were allowed t o settle in the thermostat for several weeks, and the clear liquid phase poured off from the pasty sediment. This residual lime-paste was scraped into a glass-stoppered weighing bottle, placed in a padded glass test tube and centrifuged at about 800 r. p. m. for two or three days until the solid showed no further signs of settling. The supernatant liquid was poured out of the bottle and the last few drops absorbed with clean filter paper. The weighing bottle was then weighed, the solid phase scooped out with a small platinum spoon and removed t o a long combustion boat by means of a platinum scraper. Both spoon and scraper were placed in the combustion boat which was immediately transferred to the combustion tube in place in the furnace. The closely stoppered weighing bottle was again weighed and the difference from the former weight gave the weight of the solid phase and mother liquor taken for analysis. The compositions of the solutions are given in Table I. The lime present is reckoned as Ca(OH), for convenience, especially as it was anticipated that the solid phase might prove t o be calcium hydroxide. On the other hand, there is no particular advantage in stating the results as calcium oxide. In Fig. I the calcium hydroxide in solution is plotted as a function of the sugar. The curve thus obtained is smooth,
F . K . Cameron and H . E. Patten
70
TABLEI Lime-sugar-water system at
25'
C. Liquid phase.
H,O percent
0.117' 0.188 0,73 1.355 2.31 3.21 4,57 6.07
1 I
-
0
0.62
99. I9 94,50 91.12 87.85 84.89 80.33 76.93 73.07
4.82
7.50 9.87 11.90 15,I
17.42 19.86
Fig.
Density
0.983
I .ooo 1.021
1.037 1.051 I .067 I ,092 I . 109 I . 123
I
showing no obvious breaks, and passing of course through the point for the solubility of calcium hydroxide in water alone. Consequently the solid phases in contact with the solutions represented by this isotherm must be either calcium hydroxide, or a series of solid solutions with calcium hydroxide, as a limiting solid solution at one end of the series. Attempts 'were made to determine the nature of the solid phases by the indirect method of Schreinemakers' and B a n ~ r o f t ,employing ~ the triangular diagram, but owing to the viscosity of the solutions, satisfactory separations of solid from mother liquor could not be obtained even under long centrifuging. Consequently the results were indeterminate and the method was abandoned. A solution was prepared containing 303.24 grams of water, 1
Cameron and Bell, 1. c. phys. Chem., 11, 81 (1893). Jour. Phys. Chem., 6, 178 (1902).
* Zeit. a
Solubility of Lime in Sugar Solutions
71
and IOO grams of sugar. To this solution was added 63.88 grams of calcium hydroxide. After long standing with intermittent shakings a t 25' C analysis of the supernatant solution gave 21.97 percent sugar, 8.32 percent calcium hydroxide and 69.71 percent water (by difference). The ratio of water t o sugar in the liquid phase was therefore increased by the addition of lime from 3.03-3.17, showing that sugar entered the solid phase. Consequently the solid phases were a series of solid solutions. That the absorption of sugar in the solid phase may be considerable is shown by the fact that in this particular case just cited the solid contains about 10.8 percent sugar, assuming that the ratio of lime to water remains that in calcium hydroxide. The System, Lime-Glycerol-Water at 25' This system presents experimental difficulties similar t o the one just described owing to the great viscosity of the more concentrated solutions. The solubility data are given in Table 11. When plotted they give a straight line passing through the point representing the solubility of calcium hydroxide in water. TABLEI1 Lime-glycerol-water system a t 25 ' C. Experiment number
~
Ca(OH), percent
I
C,H,(OH), percent
~
Liquid phase
H2O percent
Density
-
-
96.32 80.28
1.008
81.68 64.80 43.62
I I
-
,042 .088
1 . I49
A solution was prepared containing 35.9 percent glycerol, to which was added about 40 grams calcium hydroxide. This system was agitated for several hours in an ice bath, then allowed to come gradually t o 25'. Analysis of the supernatant solution gave 36.2 percent glycerol and 0.93 percent
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'
F . K . Cameron and H . E. Patten
lime. Evidently no glycerol entered the solid phase, and the slight apparent increase in the liquid phase can most probably be attributed to the difficulties of analysis. It is apparent that the solid phase in contact with a water glycerol solution at 25' is always calcium hydroxide. Furthermore, the solubility of calcium hydroxide is increased proportionally t o the concentration of glycerol.
Summary ( I ) Solubility isotherms for lime in solutions of sugar and of glycerol a t 25' have been determined by direct analysis of the liquid phases. ( 2 ) The solid phase in the system lime-sugar-water is one of a series of solid solutions, with calcium hydroxide a limiting case. (3) The solid phase in the system lime-glycerol-water at 25' is always calcium hydroxide. (4) The increase in solubility of lime in aqueous solutions of glycerol over that in pure water is directly proportional to the concentration of glycerol. Bureau of Soils, U . S.Debartinetit of Agriculture, Oct. 5 , 1910
