Alum.
Alum is a substance which considerably mystified the ancient chemists, who knew the salt but did not understand its composition. Ancient writers like Pliny and Dioscorides were acquainted with a product which the former called alumen and which is evidently the same as had been described by Dioscorides under the name of Stypteria. Pliny says there were several varieties of this mineral used in dyeing, and it is clear from his account that his alumen was sometimes sulphate of iron and sometimes a mixture of sulphate of iron with an aluminous earth. It is the fact that where the various vitriols are found they are generally associated with aluminous earth.
Alum as we know it was first prepared in the East and used for dyeing purposes. Alum works were in existence some time subsequent to the twelfth century at a place named Rocca in Syria, which may have been a town of that name on the Euphrates, or more probably was Edessa, which was originally known as Roccha. It has been supposed that it was the manufacture of alum at this place which bequeathed to us the name of Rock or Rocha alum, but the Historical English Dictionary says this derivation is "evidently unfounded."
The alchemists were familiar with alum and knew it to be a combination of sulphuric acid with an unknown earth. Van Helmont was the first to employ alum as a styptic in uterine hæmorrhage, and Helvetius made a great reputation for a styptic he recommended for similar cases. His pills were composed of alum 10 parts, dragon's blood 3 parts, honey of roses q.s., made into 4 grain pills, of which six were to be taken daily.
