Mucilages are viscous preparations usually employed as emulsifying or suspending agents, or as demulcents. Mucilages which are not in constant demand should be freshly prepared as required. They deteriorate when kept, especially in warm weather, unless preservatives are added, such as solution of formaldehyde (10 minims to each pint) or benzoic acid (10 grains to each pint). Mucilages which have been sterilised at 100° for ten minutes in small bottles, and securely sealed, keep for longer periods. Such precautions are unnecessary in the case of mucilage of gum acacia or mucilage of tragacanth if quantities limited to about a week's supply are stored in bottles of small size, as completely filled as possible. Mucilage of gum acacia, when required at short notice, can be rapidly prepared with hot water; the keeping properties of the product are inferior to mucilage prepared with cold water. For references to the uses of mucilages as emulsifying or suspending agents, see monographs upon gum acacia, emulsions, tragacanth, or under names of substances and preparations to be emulsified or suspended.