My talk will study the role played by Berzelian chemical formulas (such as H₂O for water) in organic-chemical experimentation form the late 1820s until the 1840s. Chemical formulas were introduced by the Swedish chemist Jacob Berzelius in 1813 in order to represent the composition of inorganic compounds according to his quasi-atomistic theory of composition. But when French and German chemists began to apply chemical formulas more broadly from the late 1820s onward, this was in organic chemistry. I will argue in the talk that chemists applied chemical formulas as paper tools to pave a way through the “jungle of organic chemistry” (F. Wöhler). Chemical formulas contributed to reduce the complexity of organic-chemical experiments. Moreover, they were helpful tools for the identification, demarcation and classification of organic compounds. The more general epistemological problem involved in these historical events concerns the role played by theory in experimental and classificatory practices. I will argue that theory was subordinated to goals emerging in scientific practice rather than the other way around.