Balneum roris

Historical definition

Balneum roris is a furnace in which the distillation vessels are placed over the water’s vapour alone, so that the vapour does not touch the body. It is also called a vaporous furnace.

Meaning

The definition’s spatial relations matter: the vessels are over vapour, and the vapour is said not to touch the body. “Body” here belongs to the material being worked rather than necessarily to the outside of the apparatus. The historical sentence is compressed, so a diagram or a more detailed passage would be needed before reconstructing every part of the arrangement.

Compare Balneum Mariæ, where the chemical vessels are placed in warm water. The distinction concerns how warmth reaches the vessel and its contents. Neither name should be read simply as a synonym for any bath or furnace. The alternative name “vaporous furnace” is useful in following different descriptions of the same stated arrangement.