Chemistry neither asserts or denies the decomposability of the elements.

At present, we have to recognise the existence of extremely small quantities, widely distributed in rocks and waters, of some thirty substances, the minute particles of which are constantly emitting streams of more minute, identical particles that carry with them very large quantities of energy, all of which thirty substances are characterised, and are differentiated from all other classes of substances wherewith chemistry is concerned, by their spontaneous mutability, and each is characterised by its special rate of change and by the nature of the products of its mutations.

We have now to think of the minute particles of two of the seventy-five or eighty substances which until the other day had not been decomposed, and were therefore justly called elements, as very slowly emitting streams of minuter particles and producing characteristic products of their disintegration.

And we have to think of some eighty substances as particular kinds of matter, at present properly called elements, because they are characterised, and differentiated from all other substances, by the fact that none of them has been separated into unlike parts.
The study of radio-activity has introduced into chemistry and physics a new order of minute particles.

Dalton made the atom a beacon-light which revealed to chemists paths that led them to wider and more accurate knowledge.