Crystallographic Studies at the Royal Institution
The practice of X-ray crystallography (and the Davy-Faraday Laboratory) was a fairly new field, and it was large enough to allow each scientist to pursue his own particular field of research with very little rivalry. Astbury chose to focus his studies on the crystalline structure of several organic compounds. He found his mathematical training to be of great help to him there, and his crystallographic knowledge, obtained from Hutchinson, to be more extensive than that of either William Bragg or his son Lawrence.
His first paper was on ‘The Crystalline Structure and Properties of Tartaric Acid’, followed by a paper on anhydrous racemic acid (a form of tartaric acid):
- He used Bragg’s ionisation spectrometer (the crystallographic method which he had been trained to use) to obtain the structure and then compares this with known physical and chemical properties to confirm his findings.
- He found a link between chemical stereoisomers and crystallographic enantiomorphs. Tartaric acid has two enantiomorphous forms: one where a beam of plane-polarised light is rotated to the right (the dextro compound), and one where it rotates to the left (the laevo compound). They are mirror images of each other and cannot be distinguished by conventional X-ray diffraction.
- Often, the technology available is not sufficient, and theoretical calculations are used instead. Good crystals of the laevo-acid were not available, and thus he could not test his theory (that the enantiomorphous forms are indistinguishable) by X-rays.
He then studied metallo-organic compounds, as described in ‘The Structure and Isotrimorphism of the Tervalent Metallic Acetylacetones’:
- Here he used both the spectrometer and photographic methods (the oscillation and rotation photographs).
- Using both of these methods he was able to determine the shape, space group and size of unit cell. He determined the positions of the molecules in the three forms by a study of the intensity distribution in a series of rotation photographs about various crystallographic axes.
- ‘Here he used the photographic method to record the intensities of 256 planes. This greater number, the largest hitherto recorded for a crystal, shows the effective superiority of the photographic method over the ionization spectrometer for organic crystals of any complexity.’ (Bernal)
His achievements at the Royal Society were not, however, strictly limited to the determination of crystal structure. He also invented a new apparatus and, with Kathleen Yardley, created the first British table of space groups, which would become the International Tables for Crystallography, Vol I.
by Imogen Clarke