Reagent Bottles are useful for storing both liquids and powders... and make a great little Rumtopf crock as well. These bottle mouth and stopper stem are machine ground.   This glass-to-glass joint is an air-tight seal without the use of a rubber or cork stopper.  ***Please note - all reagent bottles are made of Flint Glass and will contain an occasional small bubble or surface blemish. This is normal. Flint glass bottles are intended for storage only and must not be heated. For heating use a laboratory grade Borosilicate flask or beaker ****