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.
Carbon dioxide in the water reacts with the calcium hydroxide to produce calcium carbonate, some of which can react with more CO2 to become calcium bicarbonate, which is quite soluble. In summary, the solubility of calcium carbonate is quite low, and the solubility of calcium hydroxide is a little less low.