Many powdered compounds (catalysts, oxides, coals,..) are characterized by their surfaces. The measurement of physical or chemical interactions between any solute with the surface of powders characterizes their reactivity. Flow calorimetry is well-adapted method for such an investigation. The liquid percolation vessel enables the liquid to pass through the powder, deposited on a poral filter. The typical experimentation consists in using a first percolation of a carrier liquid in order to achieve the wetting of the powder. Then it is substituted by a solute and the adsorption heat of the solute on the powder is directly measured. After this process the solute is replaced by the carrier liquid and the adsorption heat is measured.