Alkaloid reagents are reagents that precipitate alkaloids. Some examples are tannic acid, picric acid, iodine and mercuric chloride. Alkaloids are vegetable compounds that are similar to ammonia and form salts by combining with acids.
Tannic acid precipitates alkaloids as white or yellowish compounds that are soluble in other acids or excess precipitate. Picric acid forms yellowish, crystalline compounds. Iodine forms brown precipitates of alkaloids, while mercuric chloride forms white to yellowish precipitates. Only a few alkaloids are liquid. Most are crystallized solids. The same is true for the salts of alkaloids. Both alkaloids and their salts are bitter in taste.