"A great many solid bodies are constantly in a state of evaporation or transformation into the gaseous state at their free surface. , , and carbonate of ammonia... if not kept in stoppered bottles, gradually disappear by evaporation, and the vapour... may be recognised by its smell and by its chemical action. ... is continually passing into a state of vapour... and in a dry climate during a long frost large pieces... [gradually] disappear. ...[[w:Iron|[I]ron]] and copper have each a well-known smell. This... may arise from chemical action at the surface, which sets free or some other gas combined with a very small quantity of the metal."