The quantitative elementary composition of cane sugar was determined early in the 19th century by Gay-Lussac and Thénard, who may be said to have virtually established our present formula, C 12 H 22 O 11 . Under Fermentation (vol. ix. p. 93) it has been explained how Gay-Lussac (in 1811) came to mis-correct his numbers so as to bring them into accordance with what we now express by C 6 H 12 O 6 = ½C 12 H 24 O 12 . Dumas and Boullay, some years later, found that cane sugar is what Gay-Lussac and Thénard’s analysis makes it out to be, while the “corrected” numbers happen to be correct for grape sugar. Dumas and Boullay’s research completed the foundations of our present science of the subject. “Sugar” is now a collective term for two chemical genera named saccharoses (all C 12 H 22 O 11 ) and glucoses (all C 6 H 12 O 6 ). All sugars are colourless non-volatile solids, soluble in water and also (though less largely) in aqueous alcohol; from either solvent they can in general be obtained in the form of crystals. The aqueous solution exhibits a sweet taste, which, however, is only very feebly developed in certain species.

All sugars and their solutions have the power of turning the plane of polarization of light. In a given solution of a given kind of sugar the angle α through which the plane is turned is governed by the equation α=±[α] lp , where l stands for the length of solution traversed (the customary unit of length being the centimetre) and p for the number of grams of dry sugar present in a volume of solution equal to that of (say) 100 grams (3·52 oz.) of water, where, however, “gram” must be taken as merely a convenient word for “unit of weight”; ±[α], i.e. the special value of α for l =l and p=l, is called the specific rotatory power of the sugar operated upon. The sign ± indicates that the plane of polarization is turned either to the right or to the left according to the nature of the species. For a given species and a given temperature [α] has a constant value. Supposing its value to have been determined by standard experiments and l to be known (or to be kept constant throughout and taken as unit of length), the determination of α for a given solution suffices for the calculation of p. This method is largely used industrially for the assaying of cane sugar.

Sugars, though neutral to litmus and inert towards such substances as carbonates on the one hand and aqueous acids (qua acids) on the other, combine with strong bases, such as caustic potash, baryta, and lime, into saccharates, and, when brought into contact with the strongest nitric acid (or a mixture of the same with oil of vitriol) or (at the proper temperature) with acetic anhydride, unite with these into nitrates and acetates respectively, with elimination of water. These nitrates, &c., are related to the respective sugar exactly as (to take an analogous case) nitrate of methyl, CH 3 (NO 3 ), is to methyl-alcohol, CH 3 (OH); only in the case of a sugar a plural of NO 3 's is capable of entering into every one molecule and turning out so many HO’s; hence sugars are said to be polyvalent alcohols. Of the several points of difference between saccharoses and glucoses the most important is that, while the latter remain unchanged when boiled with highly dilute sulphuric or hydrochloric (or certain other kinds of) acid, the former take up water and every molecule breaks up into two molecules of glucose, which in general are of different kinds. Cane sugar, for instance, yields dextrose and laevulose (so called from the direction in which they turn the plane of polarized light), thus—

C 12 H 22 O 11 + H 2 O = C 6 H 12 O 6 + C 6 H 12 0 6

Cane sugar turns the plane of polarized light to the right; the mixed glucose produced is laevo-rotatory; hence the process is spoken of technically as involving the inversion of cane sugar, and the mixed product is called invert sugar. The term “inversion,” however, has come somehow to be used for all decompositions which fall under the above equation; occasionally it is used even in a wider sense, to include any decomposition of a carbo-hydrate (e.g., starch) into two less complex carbo-hydrates.

All sugars are liable to fermentative changes; a special character of the three principal vegetable sugars is that, when brought into contact as solutions with yeast (living cells of saccharomyces), under suitable conditions, they suffer vinous fermentation, i.e. , break up substantially into carbonic acid and alcohol. Dextrose and laevulose break up directly,—C 6 H 12 O 6 = 2C 2 H 6 O + 2CO 2 . Cane sugar first, under the influence of a soluble ferment in the yeast, gets inverted, and the invert sugar then ferments, the dextrose disappearing at a greater rate than the laevulose.

It is remarkable that no sugar has ever been produced artificially even in the sense of being built up from other native organic substances of less chemical complexity. It is easy to produce dextrose from starch, or laevulose from inulin, or both from cane sugar, by inversion; but none of these processes is reversible by known methods. Yet the problem of producing cane sugar artificially may in a sense be said to have found a virtual solution at the hands of a German-American chemist, Fahlberg. Fahlberg, by subjecting toluene, C 6 H 5 CH 3 (one of the components of coal-tar naphtha), to a series of operations has produced

CO

from it a body, C 6 H 4 CONH, which he called saccharine, because he found it to be about 230 times as sweet as cane sugar. This saccharine is a white crystallized solid, only slightly soluble in cold water, but sufficiently so to admit of its incorporation with jellies, puddings, beverages, &c. A mixture of one part of it with 1000 parts of ordinary grape sugar (as produced industrially from starch) is as sweet as the best cane sugar. The substance, though an antiseptic, is said to be perfectly innocuous.

Glucoses.

Of these a pretty large number are now known, but only laevulose and dextrose need be noticed here. Both are largely present in all kinds of sweet fruit juices and in honey. In most of these materials they are accompanied by a small proportion of cane sugar, which forcibly suggests that the glucose in fruit juices is really inverted cane sugar. But, in opposition to this surmise, the proportion of cane sugar in oranges increases during the process of ripening, and the sourest of all fruits—the lemon—contains four parts of cane for every ten of invert sugar; besides, the juices of grapes and sweet cherries contain no cane sugar whatever. According to Stammer, the young leaves of the sugar cane contain abundance of invert sugar, which gradually disappears and gives way to cane sugar as the leaves develop and ultimately dry up. In the living body of man dextrose is constantly being produced from the glycogen of the liver, to be taken up by the blood and oxidized into carbonic acid and water. In certain diseases, however (see Nutrition, vol. xvii. p. 681), the sugar survives and passes into the urine; as much as one pound avoirdupois may be discharged by a diabetic patient in twenty-four hours. A numerous class of vegetable substances, known as glucosides, contain glucose of some kind in the sense that, when decomposed by boiling dilute sulphuric acid or by the action of certain ferments, they split up into glucose and some product;—not a sugar—which is characteristic of the respective species. For examples, see Fermentation, vol. ix. p. 96.

Dextrose is being produced industrially from starch by inversion (see below), and sold as grape sugar. Such grape sugar, however, is very impure. For the preparation of pure dextrose rich diabetic urine, honey, and cane sugar are convenient materials. The method recommended by Soxhlet is to dissolve 160 grams (5·64 oz.) of powdered cane sugar in a mixture of 500 c. c. of alcohol of 85 per cent. by weight and 20 c.c. of fuming hydrochloric acid at 45° C. and to allow the solution to stand. After about a week dextrose begins to crystallize out, and, if the mixture is being frequently agitated, the deposit of crystals increases gradually. A small crop of crystals thus obtained suffices for inducing crystallization in a large supply of fresh liquor. Dextrose crystallizes from its highly concentrated aqueous solution—somewhat tardily—in minute soft crystals, united into warts or cauliflower-like masses, which contain 1H 2 O of crystal water beside C 6 H 12 O 6 . The crystals lose their water at 100° C. From absolute alcohol it crystallizes as C 6 H 12 O 6 . It dissolves in 1·2 parts of cold and far less of boiling water. 100 parts of alcohol of 0·837 specific gravity dissolve 1·94 parts at 17·5 C. and 21·7 parts on boiling. In a given volume of aqueous solu- tion 5 parts of dextrose produce the same degree of sweetness as 3 parts of cane sugar. Dextrose fuses at 146 C. and at 170 passes into glucosan, C 6 H 10 O 5 , an almost tasteless solid, which when boiled with dilute sulphuric acid is reconverted into dextrose. If a solution of dextrose in absolute alcohol is saturated with hydrochloric acid gas at 0° C., di-glucose, C 12 H 22 O 11 , is produced, which, however, is only isomeric with cane sugar (Gautier).

Laevulose.— The liquid part of crystalline honey consists chiefly of laevulose; but its purification is difficult. From invert sugar it can be extracted, according to Dubrunfaut, by cautious addition of slaked lime at a low temperature. The laevulose separates out as a difficultly soluble lime compound, which is separated from the mother-liquor containing the dextrose by pressure and by judicious washing with cold water. The laevulosate of lime is decomposed by the exact equivalent of oxalic acid solution; then the oxalate of lime is filtered off, and the filtrate evaporated on a water-bath. The laevulose ultimately remains as a thick syrup, which formerly was supposed not to be susceptible of crystallization; but Jungfleisch and Lefranc have succeeded lately in obtaining crystals from it by means of alcohol. Laevulose is very largely soluble in water, and fully as sweet as cane sugar. It fuses at 95° C.; at 170° it passes into laevulosan, C 6 H 10 O 5 , analogous to glucosan.

The following reactions, though studied chiefly with dextrose, apply also to laevulose, and, substantially at least, to glucoses generally. If a solution of glucose is mixed with excess of caustic potash or soda, a solution of alkaline glucosate is formed, which, however, has little stability. If the solution is heated, the glucosate is decomposed with formation of dark-coloured (soluble) alkali salts of acid products, which, whatever they may be, are not reconvertible into glucose. Cane sugar, in these circumstances, remains substantially unchanged, and can be regenerated by elimination of the alkali. If a solution of glucose is mixed with (not too much) sulphate of copper, and an excess of caustic potash or soda be then added, no precipitate of cupric hydrate is formed, but an intensely blue solution, which, on standing in the cold gradually, and on heating promptly,‘deposits a red precipitate of cuprous oxide, Cu 2 O, the glucose being oxidized at the expense of the dissolved CuO into soluble alkali salts of little known acids. By means of this (Trommer’s) test the least trace of glucose in a solution can be discovered. Cane sugar, in the circumstances, yields cuprous oxide only on long-continued boiling. Fehling has brought this test into the following more convenient form, which, besides, admits of quantitative application: 34·6δ grams (1·22 oz.)of sulphate of copper, CuSO 4 + 5H 2 O, and 173 grams (6 oz.) of Rochelle salt (double tartrate of potash and soda) are dissolved in a solution of 70 grams (2·46 oz.) of solid caustic soda, and the intensely blue solution produced is diluted to 1000 c.c. Every c.c. of Fehling solution oxidizes about 5 milligrams (·077 grain) of dextrose (not of glucose generally). To determine an unknown weight of glucose, its solution is added to an excess of suitably diluted Fehling solution at a boiling heat, which is maintained for a sufficient time to oxidize the glucose as completely as possible,—the requisite time depending on the nature of the glucose. The cuprous oxide precipitate is allowed to settle, is then collected on a filter, and weighed directly or indirectly. From its weight the weight of the glucose is calculated,—a standard experiment with a known weight of the respective kind of pure glucose furnishing the factor. A less exact but more expeditious method is to dissolve the sugar to be analysed in water, to dilute to a known volume (not less than 200 c.c. for every gram of glucose), and to drop this solution from a burette into a measured volume of dilute Fehling solution at a boiling heat until the blue colour is just destroyed, i.e. , the copper just precipitated completely as Cu 2 O. This method is largely used in sugar-houses in the assaying of crude cane or beetroot sugars.

Saccharoses.

Of these only cane sugar, milk sugar, and maltose can be noticed here. The highest qualities of commercial cane sugar are chemically pure. Pure cane sugar crystallizes from its supersaturated syrup in colourless, transparent monoclinic prisms (exemplified in colourless candy sugar). The crystals are barely, if at all, hygroscopic; they are rather hard, and when broken up in the dark give off a peculiar kind of bluish light. Sp. gr. 1·593 at 4° C. The aqueous solution, saturated at t ° C., contains p per cent. of dry sugar. For t = 0° 10° 20° 30° 40° 50°

p = 65∙0 65·6 67∙0 69·8 75∙8 82·7.

From 50° upwards the solubility increases at such a rate that a given quantum of water dissolves any quantity of sugar if the mixture is constantly kept boiling. Accordingly a sugar syrup when boiled down deposits nothing, but passes gradually into the condition of fused sugar when the boiling-point merges into the fusingpoint of sugar, which lies at 160-161° C. Even a cold-saturated solution of sugar has the consistence of a syrup. Absolute alcohol hardly dissolves sugar at all; aqueous alcohol dissolves it the more largely the greater its proportion of water. Fused sugar freezes into a transparent glass, which is colourless if pure, but in practice generally exhibits a yellowish hue, and, if really anhydrous, remains glassy for an indefinite time. Barley-sugar and certain other confections are substantially fused sugar; but from their mode of manufacture they retain a trace of enclosed water, which constantly dissolves particles of the surrounding sugar glass to redeposit them in the less soluble form of crystals, so that barley - sugar in the course of time loses its transparency through conversion into an aggregate of minute crystals. If fused sugar is kept at a few degrees above its fusing-point for some time, it passes iuto an alloy, C 6 H 12 O 6 + C 6 H 10 O 5 , of dextrose and laevulosan (see above). At higher temperatures it loses water and passes into anhydrides not reconvertible into cane sugar, which are known in the aggregate as “caramel,”—a most intensely brown viscous solid, easily soluble in water and in aqueous alcohol, with formation of intensely coloured solutions. Caramel (often made of dextrose) is much used as an innocent colouring agent for sauces, liqueurs, &c. A pure solution of cane sugar is said to remain unchanged on boiling (it being understood, of course, that local overheating be carefully avoided); but continued contact with even so feeble an acid as carbonic induces at least partial inversion. The statement of the unchangeability of sugar solution on boiling seems hardly credible, because a syrup boiling at all considerably above 100° C. contains plenty of molecules at temperatures-above 160° C., which are bound to suffer irreversible conversion into dextrose and laevulosan (or laevulose), and even, if hot enough, caramelization. In ordinary practice, at any rate, sugar solutions on boiling do behave as indicated by this theory. Cane sugar, as already stated, unites with alkalis, alkaline earths, and other of the more strongly basic metallic oxides into saccharates. A soluble saccharate of lime, which is readily decomposible by carbonic acid and even by filtration through bone charcoal, plays a great part in the manufacture of sugar. The following strontium salt must be named, because it at least promised some years ago to occupy a similar position industrially. According to Scheibler, if strontia hydrate, SrOH 2 O + 8H 2 O, is added to a boiling 15 per cent. solution of cane sugar, then as soon as 2SrO is added for every C 12 H 22 O 11 the salt C 12 H 22 O π + 2SrO separates out as a sandy powder, and after addition of 2·5 times SrO almost all the sugar is precipitated. The precipitate is easily washed and decomposed by water and carbonic acid, with formation of insoluble carbonate of strontia (from which the hydrate can be reproduced) and a solution of cane sugar. The ultimate molasses produced in sugar making or refining, though they refuse to deposit crystals under any conditions, contain some 30 to 40 per cent. of real cane sugar; Scheibler’s process applies to them,—to put the industrial bearings of the discovery in the proper light,—and it has led to quite a series of patents for the production of strontia; but, as far as we know, it has failed to take root in the sugar industry.

Milk Sugar occurs in the milk of mammals, and it is doubtful whether it occurs anywhere else, although Bouchardat once proved its presence in a sample marked as sugar obtained from Sapota, Achras (the sapodilla of the West Indies). It is made industrially in Switzerland as a bye-product in the making of cheese. It passes into the whey, from which it is extracted by evaporation to a small volume, decolorization with animal charcoal, and crystallization. From the commercial product the pure substance can be obtained by repeated recrystallization from water, and ultimately by precipitation from the aqueous solution by alcohol. Milk sugar as it crystallizes from water under the ordinary conditions forms hydrated crystals of the composition C 12 H 22 O 11 + H 2 O; under certain conditions anhydrous crystals separate out. The hydrated crystals have pretty much the aspect of candy sugar, but they are less transparent, far harder, quite free from every soupçon of hygroscopicity, and far less sweet. They dissolve in six parts of cold and in 2·5 parts of boiling water; the solutions are not syrupy. Milk sugar is hardly soluble in alcohol. The ordinary crystals, as the formula shows, have the composition of a glucose; indeed milk sugar solution behaves to caustic alkalis and to Fehling solution as if it were a glucose. But the hydrated crystals lose their water at 130°, with formation of a residue reconvertible into the original substance by the mere action of water; besides, milk sugar is susceptible of inversion into dextrose and a specific galactose. The optical behaviour of a milk sugar solution varies according...