Chapter 5

(D. F. T.)

1Not, 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.γλυκύς, 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.

Pured-glucose, which may be obtained synthetically (seeSugar) or by adding crystallized cane sugar to a mixture of 80% alcohol and1⁄15volume 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 to3⁄5that 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 articleSugar. On reduction glucose appears to yield the hexahydric alcohold-sorbite, and on oxidationd-gluconic andd-saccharic acids. Alkalis partially convert it intod-mannose andd-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 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 α, β and γ varieties with specific rotations of 105°, 52.5° and 22°. It is now agreed that the β variety is a mixture of the α and γ. This discovery explained the mutarotation of glucose. In a fresh solution α-glucose only exists, but on standing it is slowly transformed into γ-glucose, equilibrium being reached when the α and γ 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 α and β. Lowry and Armstrong represent these compounds by the following spatial formulae which postulate a γ-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 selectiveaction of enzymes, which follows similar lines with the α- and β-glucosides,i.e.the compounds formed by the interaction of glucose with substances generally containing hydroxyl groups (seeGlucoside).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 ℔ 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.

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 α, β and γ varieties with specific rotations of 105°, 52.5° and 22°. It is now agreed that the β variety is a mixture of the α and γ. This discovery explained the mutarotation of glucose. In a fresh solution α-glucose only exists, but on standing it is slowly transformed into γ-glucose, equilibrium being reached when the α and γ 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 α and β. Lowry and Armstrong represent these compounds by the following spatial formulae which postulate a γ-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 selectiveaction of enzymes, which follows similar lines with the α- and β-glucosides,i.e.the compounds formed by the interaction of glucose with substances generally containing hydroxyl groups (seeGlucoside).

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 ℔ 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 α- and β-glucose result, which are then etherified, and if the solution be neutralized before the β-form isomerizes and the solvent removed, a mixture of the α- and β-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 γ-oxidic compounds of the formulae I., II.: The difference between the α- and β-forms is best shown by the selective action of enzymes. Fischer found that maltase, an enzyme occurring in yeast cells, hydrolysed α-glucosides but not the β; while emulsin, an enzyme occurring in bitter almonds, hydrolyses the β but not the α. 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 β-form;e.g.emulsin hydrolyses salicin, helicin, aesculin, coniferin, syringin, &c.

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’sHandbuch der organischen Chemiefor further details.

1.Ethylene Derivatives.—These are generally mustard oils, and are characterized by a burning taste; their principal occurrence is in mustard andTropaeolum 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:—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 ofPopulus 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 (seeEugenolandVanilla). Syringin, which occurs in the bark ofSyringa 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-γ-pyrone derivatives. Aesculin, C15H16O9, occurring in horse-chestnut, and daphnin, occurring inDaphne 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 inFraxinus excelsior, and with aesculin in horse-chestnut, hydrolyses to glucose and fraxetin, the monomethyl ester of a trioxycoumarin. Flavone or benzo-γ-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 inQuercus tinctoria; it hydrolyses to rhamnose and quercetin, a dioxy-β-phenyl-trioxybenzo-γ-pyrone. Rhamnetin, a splitting product of the glucosides ofRhamnus, is monomethyl quercetin; fisetin, fromRhus cotinus, is monoxyquercetin; chrysin is phenyl-dioxybenzo-γ-pyrone. Saponarin, a glucoside found inSaponaria officinalis, is a related compound. Strophanthin is the name given to three different compounds, two obtained fromStrophanthus Kombeand one fromS. 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.

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 ofPopulus 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 (seeEugenolandVanilla). Syringin, which occurs in the bark ofSyringa 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-γ-pyrone derivatives. Aesculin, C15H16O9, occurring in horse-chestnut, and daphnin, occurring inDaphne 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 inFraxinus excelsior, and with aesculin in horse-chestnut, hydrolyses to glucose and fraxetin, the monomethyl ester of a trioxycoumarin. Flavone or benzo-γ-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 inQuercus tinctoria; it hydrolyses to rhamnose and quercetin, a dioxy-β-phenyl-trioxybenzo-γ-pyrone. Rhamnetin, a splitting product of the glucosides ofRhamnus, is monomethyl quercetin; fisetin, fromRhus cotinus, is monoxyquercetin; chrysin is phenyl-dioxybenzo-γ-pyrone. Saponarin, a glucoside found inSaponaria officinalis, is a related compound. Strophanthin is the name given to three different compounds, two obtained fromStrophanthus Kombeand one fromS. 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 articleGelatinfor 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.

The separation of the fat, or “de-greasing of the bones” is effected (1) by boiling the bones with water in open vessels; (2) by treatment with steam under pressure; or (3) by means of solvents. The last process is superseding the first two, which give a poor return of fat—a valuable consideration—and also involve the loss of a certain amount of glue. Many solvents have been proposed; the greatest commercial success appears to attend Scottish shale oil and natural petroleum (Russian or American) boiling at about 100° C. The vessels in which the extraction is carried out consist of upright cylindrical boilers, provided with manholes for charging, a false bottom on which the bones rest, and with two steam coils—one for heating only, the other for leading in “live” steam. There is a pipe from the top of the vessel leading to a condensing plant. The vessels are arranged in batteries. In the actual operation the boiler is charged with bones, solvent is run in, and the mixture gradually heated by means of the dry coil; the spirit distils over, carrying with it the water present in the bones; and after a time the extracted fat is run off from discharge cocks in the bottom of the extractor.1A fresh charge of solvent is introduced, and the cycle repeated; this is repeated a third and fourth time, after which the bones contain only about 0.2% of fat, and a little of the solvent, which is removed by blowing in live steam under 70 to 80 ℔ pressure. The de-greased bones are now cleansed from all dirt and flesh by rotation in a horizontal cylindrical drum covered with stout wire gauze. The attrition accompanying this motion suffices to remove the loosely adherent matter, which falls through the meshes of the gauze; this meal contains a certain amount of glue-forming matter, and is generally passed through a finer mesh, the residuum being worked up in the glue-house, and the flour which passes through being sold as a bone-meal, or used as a manure.

The bones, which now contain 5 to 6% of glue-forming nitrogen and about 60% of calcium phosphate, are next treated for glue. The most economical process consists in steaming the bones under pressure (15 ℔ to start with, afterwards 5 ℔) in upright cylindrical boilers fitted with false bottoms. The glue-liquors collect beneath the false bottoms, and when of a strength equal to about 20% dry glue they are run off to the clarifiers. The first runnings contain about 65 to 70% of the total glue; a second steaming extracts another 25 to 30%. For clarifying the solutions, ordinary alum is used, one part being used for 200 parts of dry glue. The alum is added to the hot liquors, and the temperature raised to 100°; it is then allowed to settle, and the surface scum removed by filtering through coarse calico or fine wire filters.

The clear liquors are now concentrated to a strength of about 32% dry glue in winter and 35% in summer. This is invariably effected in vacuum pans—open boiling yields a dark-coloured and inferior product. Many types of vacuum plant are in use; the Yaryan form, invented by H. T. Yaryan, is perhaps the best, and the double effect system is the most efficient. After concentration the liquors are bleached by blowing in sulphur dioxide, manufactured by burning sulphur; by this means the colour can be lightened to any desired degree. The liquors are now run into galvanized sheet-iron troughs, 2 ft. long, 6 in. wide and 5 in. deep, where they congeal to a firm jelly, which is subsequently removed by cutting round the edges, or by warming with hot water, and turning the cake out. The cake is sliced to sheets of convenient thickness, generally by means of a wire knife,i.e.a piece of wire placed in a frame. Mechanical slicers acting on this principle are in use. Instead of allowing the solution to congeal in troughs, it may be “cast” on sheets of glass, the bottoms of which are cooled by running water. After congealing, the tremulous jelly is dried; this is an operation of great nicety: the desiccation must be slow and is generally effected by circulating a rapid current of air about the cakes supported on nets set in frames; it occupies from four to five days, and the cake contains on the average from 10 to 13% of water.

Skin Glue.—In the preparation of skin glue the materials used are the parings and cuttings of hides from tan-yards, the ears of oxen and sheep, the skins of rabbits, hares, cats, dogs and other animals, the parings of tawed leather, parchment and old gloves, and many other miscellaneous scraps of animal matter. Much experience is needed in order to prepare a goodglue from such heterogeneous materials; one blending may be a success and another a failure. The raw material has been divided into three great divisions: (1) sheep pieces and fleshings (ears, &c.); (2) ox fleshings and trimmings; (3) ox hides and pieces; the best glue is obtained from a mixture of the hide, ear and face clippings of the ox and calf. The raw material or “stock” is first steeped for from two to ten weeks, according to its nature, in wooden vats or pits with lime water, and afterwards carefully dried and stored. The object of the lime steeping is to remove any blood and flesh which may be attached to the skin, and to form a lime soap with the fatty matter present. The “scrows” or glue pieces, which may be kept a long time without undergoing change, are washed with a dilute hydrochloric acid to remove all lime, and then very thoroughly with water; they are now allowed to drain and dry. The skins are then placed in hemp nets and introduced into an open boiler which has a false bottom, and a tap by which liquid may be run off. As the boiling proceeds test quantities of liquid are from time to time examined, and when a sample is found on cooling to form a stiff jelly, which happens when it contains about 32% dry glue, it is ready to draw off. The solution is then run to a clarifier, in which a temperature sufficient to keep it fluid is maintained, and in this way any impurity is permitted to subside. The glue solution is then run into wooden troughs or coolers in which it sets to a firm jelly. The cakes are removed as in the case of bone glue (see above), and, having been placed on nets, are, in the Scottish practice, dried by exposure to open air. This primitive method has many disadvantages: on a hot day the cake may become unshapely, or melt and slip through the net, or dry so rapidly as to crack; a frost may produce fissures, while a fog or mist may precipitate moisture on the surface and occasion a mouldy appearance. The surface of the cake, which is generally dull after drying, is polished by washing with water. The practice of boiling, clarification, cooling and drying, which has been already described in the case of bone glue, has been also applied to the separation of skin glue.

Fish Glue.—Whereas isinglass, a very pure gelatin, is yielded by the sounds of a limited number of fish, it is found that all fish offals yield a glue possessing considerable adhesive properties. The manufacture consists in thoroughly washing the offal with water, and then discharging it into extractors with live steam. After digestion, the liquid is run off, allowed to stand, the upper oily layer removed, and the lower gluey solution clarified with alum. The liquid is then filtered, concentrated in open vats, and bleached with sulphur dioxide.2Fish glue is a light-brown viscous liquid which has a distinctly disagreeable odour and an acrid taste; these disadvantages to its use are avoided if it be boiled with a little water and 1% of sodium phosphate, and 0.025% of saccharine added.

Properties of Glue.—A good quality of glue should be free from all specks and grit, have a uniform, light brownish-yellow, transparent appearance, and should break with a glassy fracture. Steeped for some time in cold water it softens and swells up without dissolving, and when again dried it ought to resume its original properties. Under the influence of heat it entirely dissolves in water, forming a thin syrupy fluid with a not disagreeable smell. The adhesiveness of different qualities of glue varies considerably; the best adhesive is formed by steeping the glue, broken in small pieces, in water until they are quite soft, and then placing them with just sufficient water to effect solution in the glue-pot. The hotter the glue, the better the joint; remelted glue is not so strong as the freshly prepared; and newly manufactured glue is inferior to that which has been long in stock. It is therefore seen that many factors enter into the determination of the cohesive power of glue; a well-prepared joint may, under favourable conditions, withstand a pull of about 700 ℔ per sq. in. The following table, after Kilmarsch, shows the holding power of glued joints with various kinds of woods.

Special Kinds of Glues, Cements, &c.—By virtue of the fact that the word “glue” is frequently used to denote many adhesives, which may or may not contain gelatin, there will now be given an account of some special preparations. These may be conveniently divided into: (1) liquid glues, mixtures containing gelatin which do not jelly at ordinary temperatures but still possess adhesive properties; (2) water-proof glues, including mixtures containing gelatin, and also the “marine glues,” which contain no glue; (3) glues or cements for special purposes,e.g.for cementing glass, pottery, leather, &c., for cementing dissimilar materials, such as paper or leather to iron.Liquid Glues.—The demand for liquid glues is mainly due to the disadvantages—the necessity of dissolving and using while hot—of ordinary glue. They are generally prepared by adding to a warm glue solution some reagent which destroys the property of gelatinizing. The reagents in common use are acetic acid; magnesium chloride, used for a glue employed by printers; hydrochloric acid and zinc sulphate; nitric acid and lead sulphate; and phosphoric acid and ammonium carbonate.Water-proof Glues.—Numerous recipes for water-proof glues have been published; glue, having been swollen by soaking in water, dissolved in four-fifths its weight of linseed oil, furnishes a good water-proof adhesive; linseed oil varnish and litharge, added to a glue solution, is also used; resin added to a hot glue solution in water, and afterwards diluted with turpentine, is another recipe; the best glue is said to be obtained by dissolving one part of glue in one and a half parts of water, and then adding one-fiftieth part of potassium bichromate. Alcoholic solutions of various gums, and also tannic acid, confer the same property on glue solutions. The “marine glues” are solutions of india-rubber, shellac or asphaltum, or mixtures of these substances, in benzene or naphtha. Jeffrey’s marine glue is formed by dissolving india-rubber in four parts of benzene and adding two parts of shellac; it is extensively used, being easily applied and drying rapidly and hard. Another water-proof glue which contains no gelatin is obtained by heating linseed oil with five parts of quicklime; when cold it forms a hard mass, which melts on heating like ordinary glue.Special Glues.—There are innumerable recipes for adhesives specially applicable to certain substances and under certain conditions. For repairing glass, ivory, &c. isinglass (q.v.), which may be replaced by fine glue, yields valuable cements; bookbinders employ an elastic glue obtained from an ordinary glue solution and glycerin, the water being expelled by heating; an efficient cement for mounting photographs is obtained by dissolving glue in ten parts of alcohol and adding one part of glycerin; portable or mouth glue—so named because it melts in the mouth—is prepared by dissolving one part of sugar in a solution of four parts of glue. An india-rubber substitute is obtained by adding sodium tungstate and hydrochloric acid to a strong glue solution; this preparation may be rolled out when heated to 60°.For further details see Thomas Lambert,Glue, Gelatine and their Allied Products(London, 1905); R. L. Fernbach,Glues and Gelatine(1907); H. C. Standage,Agglutinants of all Kinds for all Purposes(1907).

Liquid Glues.—The demand for liquid glues is mainly due to the disadvantages—the necessity of dissolving and using while hot—of ordinary glue. They are generally prepared by adding to a warm glue solution some reagent which destroys the property of gelatinizing. The reagents in common use are acetic acid; magnesium chloride, used for a glue employed by printers; hydrochloric acid and zinc sulphate; nitric acid and lead sulphate; and phosphoric acid and ammonium carbonate.

Water-proof Glues.—Numerous recipes for water-proof glues have been published; glue, having been swollen by soaking in water, dissolved in four-fifths its weight of linseed oil, furnishes a good water-proof adhesive; linseed oil varnish and litharge, added to a glue solution, is also used; resin added to a hot glue solution in water, and afterwards diluted with turpentine, is another recipe; the best glue is said to be obtained by dissolving one part of glue in one and a half parts of water, and then adding one-fiftieth part of potassium bichromate. Alcoholic solutions of various gums, and also tannic acid, confer the same property on glue solutions. The “marine glues” are solutions of india-rubber, shellac or asphaltum, or mixtures of these substances, in benzene or naphtha. Jeffrey’s marine glue is formed by dissolving india-rubber in four parts of benzene and adding two parts of shellac; it is extensively used, being easily applied and drying rapidly and hard. Another water-proof glue which contains no gelatin is obtained by heating linseed oil with five parts of quicklime; when cold it forms a hard mass, which melts on heating like ordinary glue.

Special Glues.—There are innumerable recipes for adhesives specially applicable to certain substances and under certain conditions. For repairing glass, ivory, &c. isinglass (q.v.), which may be replaced by fine glue, yields valuable cements; bookbinders employ an elastic glue obtained from an ordinary glue solution and glycerin, the water being expelled by heating; an efficient cement for mounting photographs is obtained by dissolving glue in ten parts of alcohol and adding one part of glycerin; portable or mouth glue—so named because it melts in the mouth—is prepared by dissolving one part of sugar in a solution of four parts of glue. An india-rubber substitute is obtained by adding sodium tungstate and hydrochloric acid to a strong glue solution; this preparation may be rolled out when heated to 60°.

For further details see Thomas Lambert,Glue, Gelatine and their Allied Products(London, 1905); R. L. Fernbach,Glues and Gelatine(1907); H. C. Standage,Agglutinants of all Kinds for all Purposes(1907).

1This fat contains a small quantity of solvent, which is removed by heating with steam, when the solvent distils off. Hot water is then run in to melt the fat, which rises to the surface of the water and is floated off. Another boiling with water, and again floating off, frees the fat from dirt and mineral matter, and the product is ready for casking.2The residue in the extractors is usually dried in steam-heated vessels, and mixed with potassium and magnesium salts; the product is then put on the market as fish-potash guano.

2The residue in the extractors is usually dried in steam-heated vessels, and mixed with potassium and magnesium salts; the product is then put on the market as fish-potash guano.

GLUTARIC ACID,orNormal Pyrotaric Acid, HO2C·CH2·CH2·CH2·CO2H, an organic acid prepared by the reduction of α-oxyglutaric acid with hydriodic acid, by reducing glutaconic acid, HO2C·CH2·CH:CH·CO2H, with sodium amalgam, by conversion of trimethylene bromide into the cyanide and hydrolysis of this compound, or from acetoacetic ester, which, in the form of its sodium derivative, condenses with β-iodopropionic ester to form acetoglutaric ester, CH3·CO·CH(CO2C2H5)·CH2·CH2·CO2C2H5, from which glutaric acid is obtained by hydrolysis. It is also obtained when sebacic, stearic and oleic acids are oxidized with nitric acid. It crystallizes in large monoclinic prisms which melt at 97.5° C., and distils between 302° and 304° C., practically without decomposition. It is soluble in water, alcohol and ether. By long heating the acid is converted into its anhydride, which, however, is obtained more readily by heating the silver salt of the acid with acetyl chloride. By distillation of the ammonium salt glutarimide, CH2(CH2·CO)2NH, is obtained; it forms small crystals melting at 151° to 152° C. and sublimes unchanged.

On the alkyl glutaric acids, see C. Hell (Ber., 1889, 22, pp. 48, 60), C. A. Bischoff (Ber., 1891, 24, p. 1041), K. Auwers (Ber., 1891, 24, p. 1923) and W. H. Perkin, junr. (Journ. Chem. Soc., 1896, 69, p. 268).

GLUTEN,a tough, tenacious, ductile, somewhat elastic, nearly tasteless and greyish-yellow albuminous substance, obtained from the flour of wheat by washing in water, in which it is insoluble. Gluten, when dried, loses about two-thirds of its weight, becoming brittle and semi-transparent; when strongly heated it crackles and swells, and burns like feather or horn. It is soluble in strong acetic acid, and in caustic alkalis, which latter may be used for the purification of starch in which it is present. When treated with .1 to .2% solution of hydrochloric acid it swells up, and at length forms a liquid resembling a solution of albumin, and laevorotatory as regards polarized light. Moistened with water and exposed to the air gluten putrefies, and evolves carbon dioxide, hydrogen and sulphuretted hydrogen, and in the end is almost entirely resolved into a liquid, which contains leucin and ammonium phosphate and acetate. On analysis gluten shows a composition of about 53% of carbon, 7% of hydrogen, and nitrogen 15 to 18%, besides oxygen, and about 1% of sulphur, and a small quantity of inorganic matter. According to H. Ritthausen it is a mixture ofglutencasein(Liebig’s vegetable fibrin),glutenfibrin,gliadin(Pflanzenleim),glutinor vegetable gelatin, andmucedin, which are all closely allied to one another in chemical composition. It is the gliadin which confers upon gluten its capacity of cohering to form elastic masses, and of separating readily from associated starch. In the so-called gluten of the flour of barley, rye and maize, this body is absent (H. Ritthausen and U. Kreusler). The gluten yielded by wheat which has undergone fermentation or has begun to sprout is devoid of toughness and elasticity. These qualities can be restored to it by kneading with salt, lime-water or alum. Gluten is employed in the manufacture of gluten bread and biscuits for the diabetic, and of chocolate, and also in the adulteration of tea and coffee. For making bread it must be used fresh, as otherwise it decomposes, and does not knead well. Granulated gluten is a kind of vermicelli, made in some starch manufactories by mixing fresh gluten with twice its weight of flour, and granulating by means of a cylinder and contained stirrer, each armed with spikes, and revolving in opposite directions. The process is completed by the drying and sifting of the granules.

GLUTTON,orWolverine(Gulo luscus), a carnivorous mammal belonging to theMustelidae, or weasel family, and the sole representative of its genus. The legs are short and stout, with large feet, the toes of which terminate in strong, sharp claws considerably curved. The mode of progression is semi-plantigrade. In size and form the glutton is something like the badger, measuring from 2 to 3 ft. in length, exclusive of the thick bushy tail, which is about 8 in. long. The head is broad, the eyes are small and the back arched. The fur consists of an undergrowth of short woolly hair, mixed with long straight hairs, to the abundance and length of which on the sides and tail the creature owes its shaggy appearance. The colour of the fur is blackish-brown, with a broad band of chestnut stretching from the shoulders along each side of the body, the two meeting near the root of the tail. Unlike the majority of arctic animals, the fur of the glutton in winter grows darker. Like otherMustelidae, the glutton is provided with anal glands, which secrete a yellowish fluid possessing a highly foetid odour. It is a boreal animal, inhabiting the northern regions of both hemispheres, but most abundant in the circumpolar area of the New World, where it occurs throughout the British provinces and Alaska, being specially numerous in the neighbourhood of the Mackenzie river, and extending southwards as far as New York and the Rocky Mountains. The wolverine is a voracious animal, and also one with an inquisitive disposition. It feeds on grouse, the smaller rodents and foxes, which it digs from their burrows during the breeding-season; but want of activity renders it dependent for most of its food on dead carcases, which it frequently obtains by methods that have made it peculiarly obnoxious to the hunter and trapper. Should the hunter, after succeeding in killing his game, leave the carcase insufficiently protected for more than a single night, the glutton, whose fear of snares is sufficient to prevent him from touching it during the first night, will, if possible, get at and devour what he can on the second, hiding the remainder beneath the snow. It annoys the trapper by following up his lines of marten-traps, often extending to a length of 40 to 50 m., each of which it enters from behind, extracting the bait, pulling up the traps, and devouring or concealing the entrapped martens. So persistent is the glutton in this practice, when once it discovers a line of traps, that its extermination along the trapper’s route is a necessary preliminary to the success of his business. This is no easy task, as the glutton is too cunning to be caught by the methods successfully employed on the other members of the weasel family. The trap generally used for this purpose is made to resemble a cache, or hidden store of food, such as the Indians and hunters are in the habit of forming, the discovery and rifling of which is one of the glutton’s most congenial occupations—the bait, instead of being paraded as in most traps, being carefully concealed, to lull the knowing beast’s suspicions. One of the most prominent characteristics of the wolverine is its propensity to steal and hide things, not merely food which it might afterwards need, or traps which it regards as enemies, but articles which cannot possibly have any interest except that of curiosity. The following instance of this is quoted by Dr E. Coues in his work on theFur-bearing Animals of North America: “A hunter and his family having left their lodge unguarded during their absence, on their return found it completely gutted—the walls were there, but nothing else. Blankets, guns, kettles, axes, cans, knives and all the other paraphernalia of a trapper’s tent had vanished, and the tracks left by the beast showed who had been the thief. The family set to work, and, by carefully following up all his paths, recovered, with some trifling exceptions, the whole of the lost property.” The cunning displayed by the glutton in unravelling the snares set for it forms at once the admiration and despair of every trapper, while its great strength and ferocity render it a dangerous antagonist to animals larger than itself, occasionally including man. The rutting-season occurs in March, and the female, secure in her burrow, produces her young—four or five at a birth—in June or July. In defence of these, she is exceedingly bold, and the Indians, according to Dr Coues, “have been heard to say that they would sooner encounter a she-bear with her cubs than a carcajou (the Indian name of the glutton) under the same circumstances.” On catching sight of its enemy, man, the wolverine before finally determining on flight, is said to sit on its haunches, and, in order to get a clearer view of the danger, shade its eyes with one of its fore-paws. When pressed for food it becomes fearless, and has been known to come on board an ice-bound vessel, and in presence of the crew seize a can of meat. The glutton is valuable for its fur, which, when several skins are sewn together, forms elegant hearth and carriage rugs.

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