HERMETICAL Seal, among chemists, a method of stopping glass-vessels used in chemical operations, so closely, that the most subtil spirit cannot escape thro' them.
It is commonly done by heating the neck of the vessel in a flame till ready to melt, and then twisting it closely together with a pair of pincers. Or vessels may be hermetically sealed by stopping them with a glass plug, or by putting one ovum philosophorum over another.