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.
Nor is the nature of the first formed sugar certain; the general opinion has been that it is a simple hexose such as glucose or fructose, C6Hi2O,.
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.
The symptoms so closely resembled those of beri-beri that it has also been suggested that the illness was the same, and was caused by the manufacture of the glucose from mouldy rice (see Beri-Beri), though no proof of this was possible.
The general principles of stereochemistry being discussed in Stereoisomerism (q.v.), we proceed to the synthesis of glucose and fructose and then to the derivation of their configurations.
Our knowledge of the chemical structure of the monosaccharoses may be regarded as dating from 1880, when Zincke suspected some to be ketone alcohols, for it was known that glucose and fructose, for example, yielded penta-acetates, and on reduction gave hexahydric alcohols, which, when reduced by hydriodic acid, gave normal and secondary hexyliodide.
In 1895 C. Tanret showed that glucose existed in more than.
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.
Apiculatus (a common wine yeast) contains neither of these enzymes, and only ferments solutions of glucose or laevulose.
Like glucose it gives saccharates with lime, baryta and strontia.