Drying feces on a water-bath leads to considerable loss of N (mainly as ammonia) and S (mainly as sulphide) . Accurate analysis of the.se elements is possible if, in the process of drying, ammonia-free air is passed over the feces to which have been added a dilute soln. of Cu acetate in excess; the air is then passed through alkali to trap acetic and other volatile acids and then through standard acid. The alkaline fluid traps some ammonia and is then distilled into the excess acid.