19th century air analysis. Historical artwork of the equipment used by French chemists Dumas and Boussingault in the mid-19th century to determine the relative proportions of the gases in air. The equipment comprises a glass ball (left, marked B) attached to a glass tube (T) containing red hot copper in a furnace. The tap r' (centre) maintains a vacuum in these until the experiment is begun. The weights of the ball and tube are noted, and the taps opened. This draws in air through the apparatus at right, comprising filters of potash (potassium carbonate, in balls L and U-tubes f) and sulphuric acid (in balls O) and sulphuric acid and pumice (in U-tubes t). These remove carbon dioxide and water. The oxygen then reacts with the copper in T, leaving just nitrogen to pass into B, which is then reweighed.