Part 8
In _Iphigénie en Aulide_ and _Iphigénie en Tauride_, Gluck shows signs that the controversies aroused by his methods began to interfere with his musical spontaneity. He had not, in _Orfeo_, gone out of his way to avoid rondos, or we should have had no "_Che faro senza Euridice_." We read with a respectful smile Gluck's assurance to the bailli Le Blanc du Roullet that "you would not believe _Armide_ to be by the same composer" as _Alceste_. But there is no question that _Armide_ is a very great work, full of melody, colour and dramatic point; and that Gluck has availed himself of every suggestion that his libretto afforded for orchestral and emotional effects of an entirely different type from any that he had attempted before. And it is hardly relevant to blame him for his inability to write erotic music. In the first place, the libretto is not erotic, though the subject would no doubt become so if treated by a modern poet. In the second place a conflict of passions (as, for instance, where Armide summons the demons of Hate to exorcise love from her heart, and her courage fails her as soon as they begin) has never, even in _Alceste_, been treated with more dramatic musical force. The work as a whole is unequal, partly because there is a little too much action in it to suit Gluck's methods; but it shows, as does no other opera until Mozart's _Don Giovanni_, a sense of the _development_ of characters, as distinguished from the mere presentation of them as already fixed.
In _Iphigénie en Aulide_ and _Iphigénie en Tauride_, the very subtlety of the finest features indicates a certain self-consciousness which, when inspiration is lacking, becomes mannerism. Moreover, in both cases the libretti, though skilfully managed, tell a rather more complicated story than those which Gluck had hitherto so successfully treated; and, where inspiration fails, the musical technique becomes curiously amateurish without any corresponding naïveté. Still these works are immortal, and their finest passages are equal to anything in _Alceste_ and _Orfeo_. _Écho et Narcisse_ we must, like Gluck's contemporaries, regard as a failure. As in _Orfeo_, the pathetic story is ruined by a violent happy ending, but here this artistic disaster takes place before the pathos has had time to assert itself. Gluck had no opportunities in this work for any higher qualities, musical or dramatic, than prettiness; and with him beauty, without visible emotion, was indeed skin-deep. It is a pity that the plan of the great Pelletan-Damcke critical _édition de luxe_ of Gluck's French operas forbids the inclusion of his Italian _Paride e Elena_, his third opera to Calzabigi's libretto, which was never given in a French version; for there can be no question that, whatever he owed to France, the period of his greatness began with his collaboration with Calzabigi. (D. F. T.)
FOOTNOTE:
[1] Not, as frequently spelt, Glück.
GLÜCKSBURG, a town of Germany, in the Prussian province of Schleswig-Holstein, romantically situated among pine woods on the Flensburg Fjord off the Baltic, 6 m. N.E. from Flensburg by rail. Pop. (1905) 1551. It has a Protestant church and some small manufactures and is a favourite sea-bathing resort. The castle, which occupies the site of a former Cistercian monastery, was, from 1622 to 1779, the residence of the dukes of Holstein-Sonderburg-Glücksburg, passing then to the king of Denmark and in 1866 to Prussia. King Frederick VII. of Denmark died here on the 15th of November 1863.
GLÜCKSTADT, a town of Germany, in the Prussian province of Schleswig-Holstein, on the right bank of the Elbe, at the confluence of the small river Rhin, and 28 m. N.W. of Altona, on the railway from Itzehoe to Elmshorn. Pop. (1905) 6586. It has a Protestant and a Roman Catholic church, a handsome town-hall (restored in 1873-1874), a gymnasium, a provincial prison and a penitentiary. The inhabitants are chiefly engaged in commerce and fishing; but the frequent losses from inundations have greatly retarded the prosperity of the town. Glückstadt was founded by Christian IV. of Denmark in 1617, and fortified in 1620. It soon became an important trading centre. In 1627-28 it was besieged for fifteen weeks by the imperialists under Tilly, without success. In 1814 it was blockaded by the allies and capitulated, whereupon its fortifications were demolished. In 1830 it was made a free port. It came into the possession of Prussia together with the rest of Schleswig-Holstein in 1866.
See Lucht, _Glückstadt. Beiträge zur Geschichte dieser Stadt_ (Kiel, 1854).
GLUCOSE (from Gr. [Greek: glykys], sweet), a carbohydrate of the formula C6H12O6; it may be regarded as the aldehyde of sorbite. The name is applied in commerce to a complex mixture of carbohydrates obtained by boiling starch with dilute mineral acids; in chemistry, it denotes, with the prefixes d, l and d + l (or i), the dextro-rotatory, laevo-rotatory and inactive forms of the definite chemical compound defined above. The d modification is of the commonest occurrence, the other forms being only known as synthetic products; for this reason it is usually termed glucose, simply; alternative names are dextrose, grape sugar and diabetic sugar, in allusion to its right-handed optical rotation, its occurrence in large quantity in grapes, and in the urine of diabetic patients respectively. In the vegetable kingdom glucose occurs, always in admixture with fructose, in many fruits, especially grapes, cherries, bananas, &c.; and in combination, generally with phenols and aldehydes belonging to the aromatic series, it forms an extensive class of compounds termed glucosides. It appears to be synthesized in the plant tissues from carbon dioxide and water, formaldehyde being an intermediate product; or it may be a hydrolytic product of a glucoside or of a polysaccharose, such as cane sugar, starch, cellulose, &c. In the plant it is freely converted into more complex sugars, poly-saccharoses and also proteids. In the animal kingdom, also, it is very widely distributed, being sometimes a normal and sometimes a pathological constituent of the fluids and tissues; in particular, it is present in large amount in the urine of those suffering from diabetes, and may be present in nearly all the body fluids. It also occurs in honey, the white appearance of candied honey being due to its separation.
Pure d-glucose, which may be obtained synthetically (see SUGAR) or by adding crystallized cane sugar to a mixture of 80% alcohol and 1/15 volume of fuming hydrochloric acid so long as it dissolves on shaking, crystallizes from water or alcohol at ordinary temperatures in nodular masses, composed of minute six-sided plates, and containing one molecule of water of crystallization. This product melts at 86° C., and becomes anhydrous when heated to 110° C. The anhydrous compound can also be prepared, as hard crusts melting at 146°, by crystallizing concentrated aqueous solutions at 30° to 35°. It is very soluble in water, but only slightly soluble in strong alcohol. Its taste is somewhat sweet, its sweetening power being estimated at from ½ to 3/5 that of cane sugar. When heated to above 200° it turns brown and produces caramel, a substance possessing a bitter taste, and used, in its aqueous solution or otherwise, under various trade names, for colouring confectionery, spirits, &c. The specific rotation of the plane of polarized light by glucose solutions is characteristic. The specific rotation of a freshly prepared solution is 105°, but this value gradually diminishes to 52.5°, 24 hours sufficing for the transition in the cold, and a few minutes when the solution is boiled. This phenomenon has been called mutarotation by T. M. Lowry. The specific rotation also varies with the concentration; this is due to the dissociation of complex molecules into simpler ones, a view confirmed by cryoscopic measurements.
Glucose may be estimated by means of the polarimeter, i.e. by determining the rotation of the plane of polarization of a solution, or, chemically, by taking advantage of its property of reducing alkaline copper solutions. If a glucose solution be added to copper sulphate and much alkali added, a yellowish-red precipitate of cuprous hydrate separates, slowly in the cold, but immediately when the liquid is heated; this precipitate rapidly turns red owing to the formation of cuprous oxide. In 1846 L. C. A. Barreswil found that a strongly alkaline solution of copper sulphate and potassium sodium tartrate (Rochelle salt) remained unchanged on boiling, but yielded an immediate precipitate of red cuprous oxide when a solution of glucose was added. He suggested that the method was applicable for quantitatively estimating glucose, but its acceptance only followed after H. von Fehling's investigation. "Fehling's solution" is prepared by dissolving separately 34.639 grammes of copper sulphate, 173 grammes of Rochelle salt, and 71 grammes of caustic soda in water, mixing and making up to 1000 ccs.; 10 ccs. of this solution is completely reduced by 0.05 grammes of hexose. Volumetric methods are used, but the uncertainty of the end of the reaction has led to the suggestion of special indicators, or of determining the amount of cuprous oxide gravimetrically.
_Chemistry._--In its chemical properties glucose is a typical oxyaldehyde or aldose. The aldehyde group reacts with hydrocyanic acid to produce two stereo-isomeric cyanhydrins; this isomerism is due to the conversion of an originally non-asymmetric carbon atom into an asymmetric one. The cyanhydrin is hydrolysable to an acid, the lactone of which may be reduced by sodium amalgam to a glucoheptose, a non-fermentable sugar containing seven carbon atoms. By repeating the process a non-fermentable gluco-octose and a fermentable glucononose may be prepared. The aldehyde group also reacts with phenyl hydrazine to form two phenylhydrazones; under certain conditions a hydroxyl group adjacent to the aldehyde group is oxidized and glucosazone is produced; this glucosazone is decomposed by hydrochloric acid into phenyl hydrazine and the keto-aldehyde glucosone. These transformations are fully discussed in the article SUGAR. On reduction glucose appears to yield the hexahydric alcohol _d_-sorbite, and on oxidation _d_-gluconic and _d_-saccharic acids. Alkalis partially convert it into _d_-mannose and _d_-fructose. Baryta and lime yield saccharates, e.g. C6H12O6·BaO, precipitable by alcohol.
CH2OH CH2OH . . CH·OH CH·OH . . CH CH / / O< O< \ . \ . (CH·OH)2 (CH·OH2 . . HC·OH HO·CH
[alpha]-glucose [beta]-glucose
The constitution of glucose was established by H. Kiliani in 1885-1887, who showed it to be CH2OH·(CH·OH)4·CHO. The subject was taken up by Emil Fischer, who succeeded in synthesizing glucose, and also several of its stereo-isomers, there being 16 according to the Le Bel-van't Hoff theory (see Stereo-Isomerism and Sugar). This open chain structure is challenged in the views put forward by T. M. Lowry and E. F. Armstrong. In 1895 C. Tanret showed that glucose existed in more than one form, and he isolated [alpha], [beta] and [gamma] varieties with specific rotations of 105°, 52.5° and 22°. It is now agreed that the [beta] variety is a mixture of the [alpha] and [gamma]. This discovery explained the mutarotation of glucose. In a fresh solution [alpha]-glucose only exists, but on standing it is slowly transformed into [gamma]-glucose, equilibrium being reached when the [alpha] and [gamma] forms are present in the ratio 0.368:0.632 (Tanret, _Zeit. physikal. Chem._, 1905, 53, p. 692). It is convenient to refer to these two forms as [alpha] and [beta]. Lowry and Armstrong represent these compounds by the following spatial formulae which postulate a [gamma]-oxidic structure, and 5 asymmetric carbon atoms, i.e. one more than in the Fischer formulae. These formulae are supported by many considerations, especially by the selective action of enzymes, which follows similar lines with the [alpha]- and [beta]-glucosides, i.e. the compounds formed by the interaction of glucose with substances generally containing hydroxyl groups (see GLUCOSIDE).
_Fermentation of Glucose._--Glucose is readily fermentable. Of the greatest importance is the alcoholic fermentation brought about by yeast cells (_Saccharomyces cerevisiae seu vini_); this follows the equation C6H12O6 = 2C2H6O + 2CO2, Pasteur considering 94 to 95% of the sugar to be so changed. This character is the base of the plan of adding glucose to wine and beer wort before fermenting, the alcohol content of the liquid after fermentation being increased. Some fusel oil, glycerin and succinic acid appear to be formed simultaneously, but in small amount. Glucose also undergoes fermentation into lactic acid (q.v.) in the presence of the lactic acid bacillus, and into butyric acid if the action of the preceding ferment be continued, or by other bacilli. It also yields, by the so-called mucous fermentation, a mucous, gummy mass, mixed with mannitol and lactic acid.
We may here notice the frequent production of glucose by the action of enzymes upon other carbohydrates. Of especial note is the transformation of maltose by maltase into glucose, and of cane sugar by invertase into a mixture of glucose and fructose (invert sugar); other instances are: lactose by lactase into galactose and glucose; trehalose by trehalase into glucose; melibiose by melibiase into galactose and glucose; and of melizitose by melizitase into touranose and glucose, touranose yielding glucose also when acted upon by the enzyme touranase.
_Commercial Glucose._--The glucose of commerce, which may be regarded as a mixture of grape sugar, maltose and dextrins, is prepared by hydrolysing starch by boiling with a dilute mineral acid. In Europe, potato starch is generally employed; in America, corn starch. The acid employed may be hydrochloric, which gives the best results, or sulphuric, which is used in Germany; sulphuric acid is more readily separated from the product than hydrochloric, since the addition of powdered chalk precipitates it as calcium sulphate, which may be removed by a filter press. The processes of manufacture have much in common, although varying in detail. The following is an outline of the process when hydrochloric acid is used: Starch ("green" starch in America) is made into a "milk" with water, and the milk pumped into boiling dilute acid contained in a closed "converter," generally made of copper or cast iron; steam is led in at the same time, and the pressure is kept up to about 25 lb. to the sq. in. When the converter is full the pressure is raised somewhat, and the heating continued until the conversion is complete. The liquid is now run into neutralizing tanks containing sodium carbonate, and, after settling, the supernatant liquid, termed "light liquor," is run through bag filters and then on to bone-char filters, which have been previously used for the "heavy liquor." The colourless or amber-coloured filtrate is concentrated to 27° to 28° B., when it forms the "heavy liquor," just mentioned. This is filtered through fresh bone-char filters, from which it is discharged as a practically colourless liquid. This liquid is concentrated in vacuum pans to a specific gravity of 40° to 44° B., a small quantity of sodium bisulphite solution being added to bleach it, to prevent fermentation, and to inhibit browning. "Syrup glucose" is the commercial name of the product; by continuing the concentration further solid glucose or grape sugar is obtained.
Several brands are recognized: "Mixing glucose" is used by syrup and molasses manufacturers, "jelly glucose" by makers of jellies, "confectioners' glucose" in confectionery, "brewers' glucose" in brewing, &c.
GLUCOSIDE, in chemistry, the generic name of an extensive group of substances characterized by the property of yielding a sugar, more commonly glucose, when hydrolysed by purely chemical means, or decomposed by a ferment or enzyme. The name was originally given to vegetable products of this nature, in which the other part of the molecule was, in the greater number of cases, an aromatic aldehydic or phenolic compound (exceptions are sinigrin and jalapin or scammonin). It has now been extended to include synthetic ethers, such as those obtained by acting on alcoholic glucose solutions with hydrochloric acid, and also the polysaccharoses, e.g. cane sugar, which appear to be ethers also. Although glucose is the commonest sugar present in glucosides, many are known which yield rhamnose or iso-dulcite; these may be termed pentosides. Much attention has been given to the non-sugar parts of the molecules; the constitutions of many have been determined, and the compounds synthesized; and in some cases the preparation of the synthetic glucoside effected.
The simplest glucosides are the alkyl esters which E. Fischer (_Ber._, 28, pp. 1151, 3081) obtained by acting with hydrochloric acid on alcoholic glucose solutions. A better method of preparation is due to E. F. Armstrong and S. L. Courtauld (_Proc. Phys. Soc._, 1905, July 1), who dissolve solid anhydrous glucose in methyl alcohol containing hydrochloric acid. A mixture of [alpha]- and [beta]-glucose result, which are then etherified, and if the solution be neutralized before the [beta]-form isomerizes and the solvent removed, a mixture of the [alpha]- and [beta]-methyl ethers is obtained. These may be separated by the action of suitable ferments. Fischer found that these ethers did not reduce Fehling's solution, neither did they combine with phenyl hydrazine at 100°; they appear to be stereo-isomeric [gamma]-oxidic compounds of the formulae I., II.: The difference between the [alpha]- and [beta]-forms is best shown by the selective action of enzymes. Fischer found that maltase, an enzyme occurring in yeast cells, hydrolysed [alpha]-glucosides but not the [beta]; while emulsin, an enzyme occurring in bitter almonds, hydrolyses the [beta] but not the [alpha]. The ethers of non-fermentable sugars are themselves non-fermentable. By acting with these enzymes on the natural glucosides, it is found that the majority are of the [beta]-form; e.g. emulsin hydrolyses salicin, helicin, aesculin, coniferin, syringin, &c.
CH2OH CH2OH · · CHOH CHOH · · / CH / CH O < · O < · \(CHOH)2 \(CHOH)2 · · H·C·OCH3 CH3O·C·H
I. [alpha]-methyl II. [beta]-methyl _d_-glucoside _d_-glucoside
Classification of the glucosides is a matter of some difficulty. One based on the chemical constitution of the non-glucose part of the molecules has been proposed by Umney, who framed four groups: (1) ethylene derivatives, (2) benzene derivatives, (3) styrolene derivatives, (4) anthracene derivatives. A group may also be made to include the cyanogenetic glucosides, i.e. those containing prussic acid. J. J. L. van Rijn (_Die Glykoside_, 1900) follows a botanical classification, which has several advantages; in particular, plants of allied genera contain similar compounds. In this article the chemical classification will be followed. Only the more important compounds will be noticed, the reader being referred to van Rijn (_loc. cit._) and to Beilstein's _Handbuch der organischen Chemie_ for further details.
1. _Ethylene Derivatives._--These are generally mustard oils, and are characterized by a burning taste; their principal occurrence is in mustard and _Tropaeolum seeds_. Sinigrin or the potassium salt of myronic acid, C10H16NS2KO9·H2O, occurs in black pepper and in horse-radish root. Hydrolysis with baryta, or decomposition by the ferment myrosin, gives glucose, allyl mustard oil and potassium bisulphate. Sinalbin, C30H42N2S2O15, occurs in white pepper; it decomposes to the mustard oil HO·C6H4·CH2·NCS, glucose and sinapin, a compound of choline and sinapinic acid. Jalapin or scammonin, C34H56O16, occurs in scammony; it hydrolyses to glucose and jalapinolic acid. The formulae of sinigrin, sinalbin, sinapin and jalapinolic acid are:--
/ N·C3H5 / N·CH2·C6H4·OH C6H11O5·S·C < C6H11O5·S·C < \ O·SO2·OK \ O·SO2·OC16H24O5N Sinigrin Sinalbin
(CH3O)2 \ / (CH3)3 > C6H2·CH:CH·CO·C2H4·O·N < HO / \ OH Sinapin
CH3 \ > CH·CH(OH)·C10H20·CO2H C2H6 / Jalapinolic acid (Kramer)
2. _Benzene Derivatives._--These are generally oxy and oxyaldehydic compounds. Arbutin, C12H16O7, which occurs in bearberry along with methyl arbutin, hydrolyses to hydroquinone and glucose. Pharmacologically it acts as a urinary antiseptic and diuretic; the benzoyl derivative, cellotropin, has been used for tuberculosis. Salicin, also termed "saligenin" and "glucose," C13H18O7, occurs in the willow. The enzymes ptyalin and emulsin convert it into glucose and saligenin, ortho-oxybenzylalcohol, HO·C6H4·CH2OH. Oxidation gives the aldehyde helicin. Populin, C20H22O8, which occurs in the leaves and bark of _Populus tremula_, is benzoyl salicin.
3. _Styrolene Derivatives._--This group contains a benzene and also an ethylene group, being derived from styrolene C6H5·CH:CH2. Coniferin, C16H22O8, occurs in the cambium of coniferous woods. Emulsin converts it into glucose and coniferyl alcohol, while oxidation gives glycovanillin, which yields with emulsin glucose and vanillin (see EUGENOL and VANILLA). Syringin, which occurs in the bark of _Syringa vulgaris_, is methoxyconiferin. Phloridzin, C21H24O10, occurs in the root-bark of various fruit trees; it hydrolyses to glucose and phloretin, which is the phloroglucin ester of para-oxyhydratropic acid. It is related to the pentosides naringin, C21H26O11, which hydrolyses to rhamnose and naringenin, the phloroglucin ester of para-oxycinnamic acid, and hesperidin, C50H60O22(?), which hydrolyses to rhamnose and hesperetin, C16H14O6, the phloroglucin ester of meta-oxy-para-methoxycinnamic acid or isoferulic acid, C10H10O4. We may here include various coumarin and benzo-[gamma]-pyrone derivatives. Aesculin, C15H16O9, occurring in horse-chestnut, and daphnin, occurring in _Daphne alpina_, are isomeric; the former hydrolyses to glucose and aesculetin (4·5-dioxycoumarin), the latter to glucose and daphnetin (3·4-dioxycoumarin). Fraxin, C16H18O10, occurring in _Fraxinus excelsior_, and with aesculin in horse-chestnut, hydrolyses to glucose and fraxetin, the monomethyl ester of a trioxycoumarin. Flavone or benzo-[gamma]-pyrone derivatives are very numerous; in many cases they (or the non-sugar part of the molecule) are vegetable dyestuffs. _Quercitrin_, C21H22O12, is a yellow dyestuff found in _Quercus tinctoria_; it hydrolyses to rhamnose and quercetin, a dioxy-[beta]-phenyl-trioxybenzo-[gamma]-pyrone. Rhamnetin, a splitting product of the glucosides of _Rhamnus_, is monomethyl quercetin; fisetin, from _Rhus cotinus_, is monoxyquercetin; chrysin is phenyl-dioxybenzo-[gamma]-pyrone. Saponarin, a glucoside found in _Saponaria officinalis_, is a related compound. Strophanthin is the name given to three different compounds, two obtained from _Strophanthus Kombe_ and one from _S. hispidus_.
4. _Anthracene Derivatives._--These are generally substituted anthraquinones; many have medicinal applications, being used as purgatives, while one, ruberythric acid, yields the valuable dyestuff madder, the base of which is alizarin (q.v.). Chrysophanic acid, a dioxymethylanthraquinone, occurs in rhubarb, which also contains emodin, a trioxymethylanthraquinone; this substance occurs in combination with rhamnose in frangula bark.
The most important cyanogenetic glucoside is amygdalin, which occurs in bitter almonds. The enzyme maltase decomposes it into glucose and mandelic nitrile glucoside; the latter is broken down by emulsin into glucose, benzaldehyde and prussic acid. Emulsin also decomposes amygdalin directly into these compounds without the intermediate formation of mandelic nitrile glucoside. Several other glucosides of this nature have been isolated. The saponins are a group of substances characterized by forming a lather with water; they occur in soap-bark (q.v.). Mention may also be made of indican, the glucoside of the indigo plant; this is hydrolysed by the indigo ferment, indimulsin, to indoxyl and indiglucin.
GLUE (from the O. Fr. _glu_, bird-lime, from the Late Lat. _glutem_, _glus_, glue), a valuable agglutinant, consisting of impure gelatin and widely used as an adhesive medium for wood, leather, paper and similar substances. Glues and gelatins merge into one another by imperceptible degrees. The difference is conditioned by the degree of purity: the more impure form is termed glue and is only used as an adhesive, the purer forms, termed gelatin, have other applications, especially in culinary operations and confectionery. Referring to the article GELATIN for a general account of this substance, it is only necessary to state here that gelatigenous or glue-forming tissues occur in the bones, skins and intestines of all animals, and that by extraction with hot water these agglutinating materials are removed, and the solution on evaporating and cooling yields a jelly-like substance--gelatin or glue.
Glues may be most conveniently classified according to their sources: bone glue, skin glue and fish glue; these may be regarded severally as impure forms of bone gelatin, skin gelatin and isinglass.
_Bone Glue._--For the manufacture of glue the bones are supplied fresh or after having been used for making soups; Indian and South American bones are unsuitable, since, by reason of their previous treatment with steam, both their fatty and glue-forming constituents have been already removed (to a great extent). On the average, fresh bones contain about 50% of mineral matter, mainly calcium and magnesium phosphates, about 12% each of moisture and fat, the remainder being other organic matter. The mineral matter reappears in commerce chiefly as artificial manure; the fat is employed in the candle, soap and glycerin industries, while the other organic matter supplies glue.