888
SUGAR.— Properties.
of barium) until a sandy precipitate settles out.This must then be washed with water free fromcarbonic acid, in an atmosphere also free from thesame impurity. The formula indicated by the ana-lysis of the compound so prepared is C 12 H 22 O n BaO.The easy formation and purification of this bodyhave led to its being employed on a large scale as ameans of recovering sugar from molasses ; for whenprepared and washed it needs only to be decomposedby carbonic acid in order to set free the sugar, whichcan then be obtained in the solid form by evaporation.The removal of the last portions of the poisonousbaryta from the solution is easily effected by gypsum,which, of course, throws it down as insoluble sulphate.The process is due to Dubrunfaut.
The lime compounds, though very important tech-nically, are unfortunately rather indefinite in theircharacters, and it is almost impossible to purifythem so that a really satisfactory analysis can bemade. Accordingly, the most contradictory state-ments are current; but the balance of evidenceseems to point to the existence of two definitecompounds—CjjHgpOjjCaO, monobasic sucrate oflime, corresponding to the definite barium com-pound, and C 12 H 22 O n 3CaO, tribasic sucrate oflime. The first is made by dissolving lime in sugarsolution in such quantity that it is rather below thanabove the theoretical amount, filtering the stronglyalkaline solution, and precipitating by the additionof alcohol. It is soluble in water, is strongly alka-line, and absorbs carbonic acid greedily.
The tribasic sucrate is only slightly soluble, and ismuch less so in hot than in cold water; accordingly,if any solution of lime in sugar-water be heated tri-basic sucrate will be formed, and if the solution isnot too dilute, or does not contain too large a pro-portion of sugar to lime (so as to forcibly maintainthe monobasic sucrate in existence), it will separatein a more or less gelatinous form, which gives theappearance of coagulation, such as occurs with whiteof egg.
A cold solution of sugar lime rapidly absorbs car-bonic acid passed into it, but remains quite clear upto the point where about one-half of the lime is com-bined with carbonic acid; then the liquid suddenlybecomes opalescent, and, if sufficiently concentrated,gelatinous throughout. On continuing the passageof the gas the pasty mass becomes thinner andthinner as the carbonate of lime becomes more andmore crystalline, and in the end there is obtained aclear solution of sugar and a sandy precipitate ofcarbonate of lime. The gelatinous precipitate whichis formed at one stage is in all probability merelya hydrated carbonate of lime, possibly containingan excess of base, and, consequent on its physicalcharacter, entangling and retaining a certain pro-portion of whatever is in solution (e.g. the sugar)when it was formed. Boivin and Loiseau supposedthe jelly to be a definite chemical compound ofsugar lime and carbonic acid, and called it hydro-sucro-calcic-carbonate, but no one has been able toverify the analytical data. At any rate, this jelly iseasily formed on the large scale, and is applied, as
described further on, to the purification of raw sugarin the Boivin and Loiseau process, known also asthe Tooth process when applied to cane juice.
SOLUBILITY OF LIME IN SUGAR SOLUTIONS.
Quantity ofSugar Dissolvedin 100 parts ofWater.
Density ofSyrup.
Density ofSyrup whenSaturatedwith Lime.
100 parts of Residuedried at 120"contain
40*0
1*122
1-179
Lime.
21*0
Sugar.
79-0
37'5
1*116
1-175
20*8
79-2
35’0
1*110
1*166
20*5
79*5
32-5
1*103
1*159
20*3
79*7
30-0
1-096
1-148
20-1
79*9
27*5
1*089
1*139
19*9
80*1
25*0
1*082
1*128
19*8
80-2
22*5
1*075
1*116
19*3
80*7
20*0
1-068
1-104
18*8
81*2
17-5
1*060
1-092
18 7
81*3
15-0
1-052
1-080
18-5
81*5
12*5
1-044
1-067
18-3
81*7
10*0
1-036
1-053
18-1
81*9
7'5
1-027
1-040
16-9
83*1
5'0
1*018
1*026
15-3
84*7
2'5
1*009
1-014
13-8
86-2
Other bases, such as magnesia, lead oxide, ironoxide, &c., combine with sugar to form solublecompounds. Little is known about them, and to themanufacturer or refiner they are of little import-ance, except in so far that his syrups, &c., willdissolve and become contaminated with lead or ironif allowed to pass through rusty or scaly pipes orcisterns of those metals.
Sugar has the power of uniting with several saltsto form a number of definite crystalline compounds.A close study of these bodies throws much lighton the influence of “ salts ” in interfering with thecrystallization of sugar and promoting the formationof molasses. As common salt is the most com-mon saline impurity, the compounds which it formsare the most important.
When sugar is mixed with so much salt as willform about 14 per cent, of the whole mass, andthe two are then dissolved together, filtered, ren-dered slightly alkaline to prevent fermentation, andthe solution set aside to evaporate slowly in a warmplace, a viscid, somewhat treacly liquid is formed, inwhich slowly, but very slowly, crystals having theform of prisms with pyramidal ends are deposited,and continue to grow larger for a long time. Theymay be purified by solution in spirit of 10 per cent,and re-crystallization, and then have very sharply thecomposition represented by C 12 H 22 0 n NaC12H 2 0.Another compound, having the formula
2 C 12 H 28 O n , 3 NaC 14 H s Ohas also been obtained.
An iodide of sodium compound, with the compo-sition SC^H^O^SNaUSH^O, is easily obtained invery large crystals by gently evaporating at ordinarytemperatures a solution containing the two sub-stances in about the theoretical proportions.
Chloride of potassium and chloride of ammonium,when added to solutions of sugar, behave like com-mon salt so far that they make the solution viscid,and prevent the deposition of crystals of pure sugar.