Solvay process [for Ernest Solvay], commercial process for the manufacture of sodium carbonate (washing soda). Ammonia and carbon dioxide are passed into a saturated sodium chloride solution to form soluble ammonium hydrogen carbonate, which reacts with the sodium chloride to form soluble ammonium chloride and a precipitate of sodium hydrogen carbonate (sodium bicarbonate) if the temperature is maintained below 15°C;. The sodium hydrogen carbonate is filtered off and heated to produce sodium carbonate.