but the term 'alum' only applies to aluminium potassium sulphate (reviewed in Ref. 46) (see the table). Alum was used by Alexander Glenny and captures antigen by precipitation when the solution is ...

Kelley, Southard and Anderson 1 have shown that the thermodynamic properties of calcium sulphate hemihydrate ... there would also be some hemihydrate crystals having properties intermediate ...