Eudiometer designed by Volta. Consists of a funnel-shaped brass base to collect gases from a pneumatic trough, a stop-cock, and a tube with, at its top, a brass collar with a spark gap terminating in a brass ball. The instrument resembles Volta's final version of 1790, but the glass tube is not graduated, perhaps because it is a modern replacement. The tube was filled with water and placed upside down in the trough, which was also filled with water. A mixture of air and hydrogen was then introduced, displacing the liquid. The mixture was exploded by an electric spark that made the hydrogen react with the oxygen in the air, producing a small quantity of steam that condensed. After the reaction, the water would rise back up the tube to a given height. From this one could determine the volume of the nitrogen that had not taken part in the reaction but had remained in the tube. Provenance: Lorraine collections.