CHAPTER IX.

_THE PHYSICAL CHEMISTRY OF THE HIDE-FIBRE._

Causes of swelling and contraction -- The essentials of the tanning process -- The constitution of matter -- The nature of molecules -- Vapour-pressure -- Surface-tension -- Solution-pressures -- Jellies -- Crystals -- Osmotic pressure -- Electrolytic dissociation -- Electrolysis -- Reactions of ions -- Absorption of water by gelatine -- Dehydration by alcohol -- Action of acids, alkalies and salts on gelatinous fibre -- Physical explanation of swelling -- Action of acids on gelatine -- Action of alkalies on gelatine -- Effect of salt -- The pickling process PAGE 73