CHO CHO CH{2}(OH) CH(OH) │ │ │ ║ HCOH HOCH CO COH │ │ │ │ HOCH HOCH HOCH HOCH │ │ │ │ HCOH HCOH HCOH HCOH │ │ │ │ HCOH HCOH HCOH HCOH │ │ │ │ CH{2}(OH) CH{2}(OH) CH{2}(OH) CH{2}(OH) Glucose. Mannose. Fructose. Enolic form. This enolic form is capable of giving rise to all three hexoses, and the change by which the enolic form is produced and converted into an equilibrium mixture of the three corresponding hexoses is catalytically accelerated by alkalis, or rather by hydroxyl ions. In neutral solution the change is so slow that it has never been experimentally observed; in the presence of decinormal caustic soda solution at 70° the conversion is complete in three hours. Precisely similar effects are produced with galactose, which yields an equilibrium mixture containing talose and tagatose, sugars which appear not to be fermentable. The continued action even of dilute alkaline solutions carries the change much further and brings about a complex decomposition which is much more rapidly effected by more concentrated alkalis and at higher temperatures. This change has been the subject of very numerous investigations [for an account of these see E. v. Lippmann, 1904, pp. 328, 713, 835], but for the present purpose the results recently obtained by Meisenheimer [1908] may be quoted as typical. Using normal solutions of caustic soda and concentrations of from 2 to 5 grams of hexose per 100 c.c., it was found that at air temperature in 27 to 139 days from 30 to 54 per cent. of the hexose was converted into inactive lactic acid, C{3}H{6}O{3}, from 0·5 to 2 per cent. into formic acid, CH{2}O{2}, and about 40 per cent. into a complex mixture of hydroxy-acids, containing six and four carbon atoms in the molecule. Usually only about 74 to 90 per cent. of the sugar which had disappeared was accounted for, but in one case the products amounted to 97 per cent. of the sugar. About 1 per cent. of the sugar was probably converted into alcohol and carbon dioxide. No glycollic acid, oxalic acid, glycol, or glycerol was produced. The fact that alcohol is actually formed by the action of alkalis on sugar was established by Buchner and Meisenheimer [1905], who obtained small quantities of alcohol (1·8 to 2·8 grams from 3 kilos. of cane sugar) by acting on cane sugar with boiling concentrated caustic soda [p098] solution. It is evident that under these conditions an extremely complex series of reactions occurs, but the formation of alcohol and carbon dioxide and of a large proportion of lactic acid deserves more particular attention.