Fibroin is insoluble in water, acids and alkalies; silk-glue resembles gelatin in its solubility, but it is less readily gelatinized.
Some solutions of nitroglycerin (in ether, acetone, &c.) burn quietly, and the same is the case when it is held in solution or suspension in a colloid substance, as gelatinized guncotton, &c.
The employment of guncotton as a propellant was possible only after the discovery that it could be gelatinized or made into a colloid by the action of so called solvents, e.g.