Читать книгу A Text-book of Paper-making - C. F. Cross - Страница 26

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—The ligno-celluloses undergo a profound modification when heated with water at elevated temperatures. They are to a great extent converted into soluble products, of which a large proportion are the volatile bodies, acetic and formic acids and furfural. The residual fibre is found to be more or less disintegrated, and of a dark-brown colour, but preserving many of the chemical features of the original. A similar disintegration is caused by exposing the ligno-celluloses in a dry state to an atmosphere of superheated steam, the effect being much increased if the ligno-cellulose be previously bleached by any of the ordinary {22} processes, i.e., under oxidising conditions. In these decompositions oxidation, as well as hydration, plays an important part. It is found that the presence of small quantities of reducing agents, e.g., sulphites, exerts a remarkable effect in retarding and often entirely preventing these changes. It is probable that they act in obviating an initial change, which, with a cumulative reaction on the fibre, effects the profound resolutions above described. (See p. 71.)