Chemical crystallography before X-rays

Chemical crystallography before X-rays describes how chemical crystallography developed as a science up to the discovery of X-rays by Wilhelm Conrad Röntgen in 1895. In the period before X-rays, crystallography can be divided into three broad areas: geometric crystallography culminating in the discovery of the 230 space groups in 1891–4, physical crystallography and chemical crystallography.

Up until 1800 neither crystallography nor chemistry were established sciences in the modern sense; as the 19th century progressed both sciences developed in parallel. In the 18th century chemistry was in a transitional period as it moved from the mystical and philosophical approach of the alchemists, to the experimental and logical approach of the scientific chemists such as Antoine Lavoisier, Humphry Davy and John Dalton.^[1]

Before X-rays, chemical crystallographic research involved observation using a goniometer,^[2] a microscope, and reference to crystal classes, tables of crystal angles, axial ratios, and the ratio between molecular weight and density (M/ρ).^[3] In this period crystallography was a science supported by empirical laws (law of constancy of interfacial angles, law of rational indices, law of symmetry) based on observations rather than theory.^[4]

The history of chemical crystallography covers a broad range of topics including isomorphism, polymorphism, molecular chirality and the interaction with mineralogy, structural chemistry and solid-state physics.^[5]