Examples of index fossils. Index fossils (also known as guide fossils, indicator fossils or zone fossils) are fossils used to define and identify geologic periods (or faunal stages).
Methyl cellulose. Methyl cellulose (or methylcellulose) is a chemical compound derived from cellulose. It is a hydrophilic white powder in pure form and dissolves in cold (but not in hot) water, forming a clear viscous solution or gel.
Ionic substances are insoluble in non-polar solvents such as cyclohexane. They are soluble in water (a polar solvent) although in some cases the solubility is only small (e.g. CaCO3). When an ionic compound dissolves in water, the ions in the crystal lattice become separated and surrounded by water molecules forming hydrated ions (see p6). H2O