1. A body capable of swelling, when put into water, absorbs a definite quantity of the water up to a maximum, which cannot be exceeded. (C. Ludwig.)
2. The maximum of swelling depends upon the chemical composition of the body, on its cohesion and elasticity, and on the temperature and interior pressure of the liquid. (C. Ludwig.)
3. Power of resistance to swelling increases from the exterior to the interior, according to a parabolic law; i.e. the external layers of the body attain the maximum swelling sooner than the internal portions. (L. Mathiessen and A. Schwarz.)
4. The volume of the swollen body is smaller than its original volume, plus that of the liquid absorbed. (Quincke.)
5. Swelling is accompanied by development of heat.[53]
The production of heat is simply due to the contraction, and not to any chemical phenomenon, such as hydration.[54] This explains a fact well known to tanners, viz. that skins swell in cold water and “fall” in warm water. Riecke[55] concludes that the degree of swelling, m2/M (where m2 = mass of water absorbed, M = mass of the body swollen), in a space filled with aqueous vapour, unsaturated, is a function of the pressure and temperature.
The velocity of swelling (Pascheles) may be expressed by the formula—
dQ/dt = (M – Q) K
where M = maximum of swelling, Q = amount of swelling in the time t, and K = a constant.