When Descartes touches upon objects and operations of chemistry in the fourth part of Principia philosophiae (1644), he destroies any possibility of chemistry to become a specific science. He reduces all chemical operations to matters of size, shape and motion of particles. In the frame of Cartesian natural philosophy, chemistry vanishes into mechanics. In this article, I would like to examine how, under these conditions, Cartesian philosophers introduce chemical discourse in their natural philosophy. Some of them, such as Boyle, said that the mechanical structure underlies all chemical operations. Therefore, chemistry can only exist as empirical knowledge. Others nowever, such as Lémery (father and son) proposes new mechanical explanations specific to chemistry, in a way which is opposite to the theories of Principia philosophiae. Chemistry, which cannot be developped without laboratory works, leads to an unusual empirical cartesianism which I suggest to examine in the light of the debate between some French chemists at the Académie royale des sciences at the end of 17th century and the beginning of 18th century.