The theory of phlogiston ( a substance at the root of all combustion ) was propounded by the German Georg Ernst Stahl in the early 18th century and was only overturned by the end of the century by the French chemist Antoine Lavoisier , the chemical analogue of Newton in physics ; who did more than any other to establish the new science on proper theoretical footing , by elucidating the principle of conservation of mass and developing a new system of chemical nomenclature used to this day .