The crystals of beet-root sugar are longer and flatter than those furnished by sugar from the cane, but they cannot otherwise be distinguished from the latter.

The manufacture of sugar from this root was called into existence by the wars of Napoleon, during which the ordinary supply of the article was cut off from the French. In France, where the principal manufactories of this sugar exist, a good deal of the molasses, which is inferior to that of the cane, is fermented, and furnishes a considerable quantity of spirit of wine, amounting in weight to nearly one-third of the treacle employed; this spirit is purified by distillation: the residuum is evaporated to dryness, and then incinerated for the sake of the alkaline salts which it yields; these salts consist principally of potassic and sodic carbonates, with a small proportion of potassic sulphate and chloride. Beet-roots contain a large proportion of soluble saline matters, which are by this means economized. The crushed pulp is either employed while fresh as food for cattle, or used as manure for the land.

(1089) Refining of Sugar. The process of refining sugar, whether from the cane or the beet-root, is alike for each. Two or three parts of sugar are dissolved in one part of lime-water mixed with 3 or 4 per cent. of bone black, and the whole is heated in large cisterns by allowing steam to blow up into them through pipes which open into the bottom of the vessel; from these cisterns the syrup is transferred to a filtering apparatus consisting of tubes of twilled cotton, where it is freed from mechanical impurities, and runs through as a reddish brown syrup. Formerly this clarification was aided by adding to the syrup a certain quantity of the serum of bullock's blood. The albumin of the serum, on the application of heat, became coagulated and rose to the surface, carrying with it entangled in its meshes the greater part of the solid impurities, which were afterwards removed by skimming.

The reddish syrup which has run through the filters has next to be freed as much as possible from colouring matter, and for this purpose it is a second time filtered; but the filter on this occasion is of a different nature, and consists simply of a bed of animal charcoal, prepared by calcining bones in closed vessels, and subsequently grinding them into a coarse powder. The filters consist of extensive vats twelve or fourteen feet deep, and sometimes much deeper, with perforated false bottoms; upon these a layer of ticking is placed, and above this charcoal to the depth of twelve feet or more; above this is another layer of ticking covered with

a perforated metallic plate. The syrup is allowed to flow evenly over the surface, and by the time it has run through it is colourless (54).

Owing to the viscidity of the filtered liquid, a high temperature (230° F. or 110° C.) is necessary to make it boil under ordinary circumstances and at this temperature the sugar quickly passes into the uncrystallizable modification, especially when exposed to the action of the atmosphere. By an ingenious application of the mode in which liquids may be boiled in vacuo at a temperature far below their ordinary boiling point (182), this difficulty has been in a great measure overcome; and the syrups are now universally boiled down in the vacuum pan. In this apparatus the pressure of the atmosphere is removed by means of a powerful air-pump, and a partial vacuum is maintained above the surface of the liquid in the evaporating vessel, which is a closed pan or boiler constructed of a spheroidal form, in order to enable it to resist the pressure of the external atmosphere. The lower half of the pan is double, for the purpose of admitting steam between the coatings; and a spiral steam pipe is also coiled within the boiler, with a view of increasing the extent of heating surface. By this arrangement a supply of steam can be admitted from a neighbouring boiler, the heat being sufficient to cause the syrup to enter in rapid ebullition, whilst all danger of burning the syrup is completely avoided; since the boiling point does not rise above 150° or 158° (7c° C.). The evaporation is continued until a small quantity of the liquid when placed between the thumb and finger can be drawn out into a thread which breaks near the thumb and curls back to the finger. When it reaches this point the syrup is emptied into a vessel heated by steam to about 170°; in this heater it is strongly agitated with wooden oars until it appears to be thick and granular. It is upon this agitation in the heater that the whiteness and fineness of the grain in refined sugar depend. Fresh portions of the evaporated liquor are two or three times added to the first, and thus the temperature is alternately raised and suffered to fall. From the heating vat it is transferred into inverted conical moulds, either of sheet iron or of unglazed earthenware; in the apex of each of these is an aperture, which is at first closed by means of a plug. The syrup is again well stirred in these moulds, to favour the escape of airbubbles, which would otherwise give the mass a honeycombed appearance. After this operation it is left at rest for several hours, at the end of which time the plug is removed, and the uncrystallized syrup runs into vessels placed below for its reception. The

ACTION OF NITRIC ACID ON THE SUGARS.

111

sugar, however, is not yet white; for though the crystals consist of pure sugar, the loaves retain mechanically a large quantity of coloured syrup. In order to get rid of this, a quantity of fine colourless syrup is poured upon the base of each loaf, and this syrup, as it gradually percolates through the porous mass, displaces the impurities. The loaf is finally dried in a heated chamber, and finished for the market by turning it in a lathe.

In many refineries, after the finest quality of sugar has been obtained in the form of loaves in the manner already described, the syrup which drains from them is boiled down again in the vacuum pan, and is obtained in the form of what is termed crushed sugar, which is freed from the uncrystallized syrup with great rapidity by an ingenious application of the centrifugal force. The apparatus employed is similar in principle to that which has been long used for drying clothes in laundries. It consists of a cylindrical drum mounted upon a vertical axis, to which a very rapid rotatory movement can be given. The outer wall of this revolving drum is formed of a stout but close metallic network. This drum is enclosed in a second somewhat larger fixed cylindrical vessel, in which the liquid portion of the syrup is collected. In order to use the apparatus, a charge of concentrated syrup, which has been allowed to cool, and has thus become converted into a crystalline magma, is transferred to the inner drum of the centrifugal machine. The drum is now put into rapid rotatory motion, the uncrystallized syrup escapes through the pores of the metallic gauze, whilst the crystals are retained upon its inner surface. Between the withdrawal and the introduction of each charge the drum is cleansed by a jet of high-pressure steam, and thus the pores of the metallic network are kept clear.

(1090) Action of Nitric Acid on the Sugars.-The action of nitric acid upon the different varieties of sugar is remarkable and characteristic. Sucrose and dextrose, when treated with 3 times their weight of nitric acid, of sp. gr. 127 (care being taken that the temperature be not allowed to rise beyond 158° (70° C.), yield a peculiar acid, the saccharic; and the same substance may also be obtained from starch, gum, and lignin by similar treatment.

2 6 8

Saccharic Acid (H,H ̧ ̧).—This acid forms a colourless, inodorous, deliquescent, gummy, uncrystallizable mass, which is freely soluble in alcohol, but sparingly so in ether. It yields two salts with potassium, one of which is the normal salt; this contains 2 atoms of metal to 1 of acid, and is very soluble; the other is a sparingly soluble acid saccharate which crystallizes in

112

MUCIC AND PYROMUCIC ACIDS.

oblique rhombic needles. Saccharic acid is sufficiently powerful to dissolve iron and zinc with extrication of hydrogen. Its normal barytic salt is amorphous and sparingly soluble. Saccharic acid has a tendency to form double salts, so that it appears to be dibasic.

If sucrose or dextrose be acted upon by nitric acid of a specific gravity higher than 127, and the temperature be allowed to rise, a large quantity of oxalic acid is formed.

Mucic Acid (H,H).-Sugar of milk, when treated with excess of nitric acid, furnishes mucic acid, accompanied by saccharic acid, with which the mucic is isomeric; mucic acid may also be produced from gum and mannite by similar treatment. When sugar of milk is used, Liebig found the mother-liquor to contain tartaric acid; indeed it may be remarked that one molecule of mucic acid contains the elements of one molecule each of tartaric and acetic acids, for

One part of gum or of sugar of milk, when boiled with 4 parts of nitric acid of sp. gr. 135 and I part of water, on cooling deposits mucic acid in minute, colourless, transparent, tabular crystals, which assume the appearance of a sparingly soluble white gritty powder, insoluble in alcohol. It is a dibasic acid, the salts of which are all insoluble in water with the exception of those of the metals of the alkalies: it forms two classes of salts, a normal and an acid scries. Normal potassic mucate consists of 2 K‚¤¿н ̧Ð ̧‚н2; the acid mucate of the same metal, of 2 KHЄн ̧Ð ̧‚Í‚. Mucic acid is soluble in concentrated sulphuric acid, with which it forms a crimson solution.

2

6 8 89 2

8

When mucic acid is heated, carbonic anhydride and water are expelled, and a new monobasic acid, the pyromucic (HЄ,H ̧ ̧), is sublimed in delicate needles :

Pyromucic is isomeric with pyromeconic acid, but it is distinguished from this body by the formation of a white insoluble precipitate when added to a solution of basic acetate of lead.

If mucic acid be simply boiled in water for some time, it passes into an isomeric variety known as paramucic acid, which is much more soluble in water than mucic acid, and is also freely

VARIETIES OF SUGAR.

113

taken up by alcohol; when its aqueous solution is evaporated, paramucic acid is left in quadrangular tables.

(1091) The action of polybasic acids upon the sugars gives rise to a remarkable series of bodies which we shall describe hereafter (1246). The products thus obtained lead to the conclusion that glucose is intimately connected with the class of polyatomic alcohols.

Some steps have been made recently towards the artificial production of sugar. Amongst the products obtained from oxalic ether by the action of sodium amalgam (1324) Löwig found a fermentable sugar, and Carius has procured from benzol a variety of sugar which he calls phenose (1548).

The following table contains a summary of the leading characters of the principal varieties of sugar, including those of a few saccharine substances of less importance-viz., trehalose, (a term taken from trehala, the commercial name for Turkish manna), melezitose, (from melèze, the French name for the larch), sorbin, dulcite, quercite, (from quercus the oak, indicative of its origin in the acorn), and pinite, none of which it will be necessary to describe more minutely.

Sugars and some allied Bodies.

VARIETY AND ORIGIN OF SUGAR.

PRINCIPAL PROPERTIES.

Crystallizes in four or six-sided rhomboidal prisms-is very soluble in water, less so in diluted alcohol-sp. gr. 1·6—fuses at about 320° (160° C.)-is not precipitated by subacetate of lead, but is so by an ammoniacal solution of acetate of lead-does not reduce an alkaline solution of potassio-cupric tartrate on boilingproduces right-handed rotation = 73°S,-undergoes alcoholic fermentation with yeast-combines with alkalies-yields dextrose and lævulose when boiled with dilute acids-with nitric acid yields saccharic and oxalic acids.

Is not crystallizable-is soluble in dilute alcohol-is not precipitated by subacetate of lead-reduces an alkaline solution of potassio-cupric tartrate by boiling-produces left-handed rotation -26° at 59° (15° C.)-undergoes alcoholic fermentation with yeast -turns brown when treated with alkalies-is partially converted into grape sugar by boiling with dilute acids.

Crystallizes in cubes or square tables-is less soluble in water than cane sugar, but more soluble in alcohol-yields a precipitate with ammoniacal acetate of lead-reduces potassio-cupric tartrate, and the salts of mercury, silver, and gold when boiled with them-ferments readily with yeast-produces right-handed rotation 57°4-becomes brown when treated with alkalies-with nitric acid yields saccharic and oxalic acids.