GLUCOSE (or, more correctly, GurcosE), known also as GRAPE SUGAR, STARCII SUGAR and DIABETIC SUGAR seldom occurs in distinct, well-formed crystals, but may be obtained in warty concretions, which, when examined under the microscope, are found to consist of minute rhombic tablets. It never; however, crys tallizes readily. It is less sweet than ordinary (cane) sugar, and is soluble iu water and in dilute alcohol. There are two varieties, distinguished by their action on polarized light—dextroglucose, which turns the plane of polarization to the right, and lavoglucase, Which turns it to the left. At 212° it fuses, and loses its water of crystallization, and at a higher temperature (about 400°) it undergoes change, loses the elements of water, and becomes converted into Caramel a brown substance, which is neither sweet nor capable of undergoing fermentation, but which is readily soluble in water, and is much used by cooks and confectioners as a coloring matter. At a still higher temperature, it becomes entirely decomposed into carbonic oxide, carbonic acid, light carbureted hydrogen (Cal.,), acetic acid, aldehyde, furfurol, and a very bitter sub stance, to which the name assamar has been applied.
With bases, glucose forms various definite but unstable compounds, which have been termed sacclwrates, a term which ought to have been restricted to the salts of saccharic acid. On heating an alkaline solution of glucose, decomposition ensues, and a dark-brown uncrystallizable substance is formed, which possesses acid properties, and is known as melassic acid. This reaction is sometimes employed for the detection of glucose, and is known as Moore's test.
Glucose has a strong reducing power, and upon this property several of its tests based. It reduces the oxide of copper; even without the aid of heat, in alkaline solu tions to the state of the yellow this reaction is apparent when only 0.0001 of glucose is present in the fluid. This is known as Trommer's test, and Fehling's mode of determining glucose quahtitatively is based on the same reaction. In consequence of this, reducing power, sugar is sometimes employed in the solution of the silver salts used for the silvering of mirrors.
Glucose readily undergoes fermentation. On mixing a solution of it, kept at a mod erate temperature, with yeast, each equivalent of it breaks up into two equivalents of alcohol, and four equivalents of carbonic acid, or— Glucose. Alcohol. Carbonic Acid.
Cl2F112012 = 2(0411602) 400, Under the influence of other exciters of fermentation, as, for instance, putrid animal membranes, or other nitrogenous substances, glucose becomes converted first into lactic acid, and subsequently into butyric acid. reactions are exhibited in the two fol lowing formula: Glucose. Lactic Acid. Butyric Acid. Carbonic Hydro.
Cii11190is = = CERBO., 4CO3 4H Under certain conditions, which are not accurately known, solutions of glucose undergo a change which is termed viscous fermentation. *The sugar becomes converted into a viscous or ropy substance, while lactic acid and mannite (C12II14012) are formed. This kind of fermentation sometimes occurs it light-bodied white wines. Water is probably decomposed, and its hydrogen unites with a portion of the glucose to form mannite.
Glucose is a constituent of the juice of grapes, plums, cherries, figs, and many other sweet fruits, and may often be observed in a crystalline form on raisins, dried figs, etc. It likewise occurs in honey. In the animal kingdom, it is found sometimes as a normal and sometimes as a pathological constituent of various fluids and tissues. Thus, it occurs normally in the contents of the small intestine, and in the chyle after the use of amylaceous and saccharine food, in the blood of the hepatic veins (See LIVER); in the tissue of the liver, in both the yolk and white of birds' eggs, in the urinary secretion in minute quantity (according to Brflcke, Bence, Jones, and others), etc.; while in the disease known as diabetes, it exists in large quantity in the urinary secretion, and may be detected in nearly all the fluids of the body. By injuring a certain part. of the medulla oblongata (the part of the spinal cord contained within the cavity of the cra nium), an artificial diabeteS can be produced.