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 period of his greatness began with his collaboration with Calzabigi.

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. , 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 ) or by adding crystallized cane sugar to a mixture of 80% alcohol and 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 to  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. 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.

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 and ). 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, and  varieties with specific rotations of 105°, 52.5° and 22°. It is now agreed that the variety is a mixture of the  and. This discovery explained the mutarotation of glucose. In a fresh solution -glucose only exists, but on standing it is slowly transformed into -glucose, equilibrium being reached when the and 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 and. Lowry and Armstrong represent these compounds by the following spatial formulae which postulate a -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 