I don’t, I freely admit, remember all that much about my chemistry lessons at school. Covalent bonding delighted me not, no, nor moles neither. But I do recall being absolutely thrilled the first time I saw paper chromatography. The idea was – I expect I’m getting this slightly wrong, but don’t write in – that you’d take some murky liquid that was a solution of all sorts of this that and the other, and you’d dab it on a bit of blotting paper, which would then be stood in a basin of some solvent…

All this splitting, all this factional baring-of-the-differences,...