À Karl Marx, le 16 juin 1867

Have read Hofmann. For all its faults, the latest chemical theory does represent a great advance on the old atomistic theory. The molecule as the smallest part of matter capable of independent existence is a perfectly rational category, “a nodal point,” as Hegel calls it in the infinite progression of subdivisions, which does not terminate it, but marks a qualitative change. The atom — formerly represented as the limit of divisibility — is now but a state although Monsieur Hofmann himself is forever relapsing into the old idea that indivisible atoms really exist. For the rest, the advances in chemistry that this book records are truly enormous, and Schorlemmer says that this revolution is still going on day by day, so that new upheavals can be expected daily.