1) Aqueous solution of drug gives precipitate with solution of trinitrophenol and solution of tannic acid.
2) On heating gelatin solution with soda lime, ammonia gas is evolved.
3) Aqueous solution of gelatin precipitates mercuric nitrate solution forming white colour,
which turns black-red on heating.
4) Formaldehyde makes gelatin hard & insoluble after drying.
5) To aqueous solution of drug, add drop of picric acid or tannic acid solution, precipitate is produced.