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.
Do note that solubility of ionic compounds are not absolute. In fact, solubility in water is often given as a value in g/L of water. However, generally, we define solubility as: 1  Soluble substances can form a 0.1M solution at 25 Â°C. 2  Insoluble substances cannot form a 0.1M solution at 25 Â°C.t's just not as immediate as dissolution of the more soluble ionic compounds. You are probably familiar with this phenomenon: This forms because calcium carbonate dissolves. The rock is limestone, which is usually composed of pure calcium carbonate.