Abstract
The body material of paper is the vegetable fibre. Consisting mainly of cellulose, which because of its chemical character shows high hygroscopicity, the fibres enable the paper to take up water in its liquid phase, as well as in its vapour phase. The moisture content of the paper resulting from such absorption depends on the relative humidity and on the temperature of the surrounding air, on the composition (furnish) of the paper, on the manufacturing processes such as drying, also on the beating of the stock. These correlations are described.
Combined with changes in the moisture content are changes in the paper dimensions: their size is essentially given by the shrinkage of the paper during drying. As far as this shrinking is concerned, beating of the paper stock plays an important role. A special effect of dimensional instability is cockling.
The paper deals with the theories put forward by several authors who have investigated these correlations. It closes with some results obtained by using a new apparatus for measuring the hydrostability and the hygrostability of papers.
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