There are a considerable number of materials that possess the property of forming highly viscous, colloidal solutions in surprisingly low concentrations. To this class belong certain proteins, agar, starch, rubber, cellulose, nitrocellulose, cellulose acetate, and synthetic polymerized substances, such as polystyrene, polyvinyl chloride, polyvinyl acetate, etc. It is not uncommon for one per cent solutions to have viscosities several hundred or thousand per cent greater than that of the solvent, whereas equal concentrations of chemically related substances, such as albumin, styrene, etc., may cause an increase of but a few per cent.