(for ammonia in urine) one based on the action of formaldehyde on ammonia salts. A 10 per cent solution of sodium carbonate is slowly added to urine until the reaction becomes neutral. A 40 per cent solution of formaldehyde is neutralized with a one-fourth normal sodium solution against phenolphthalein until it becomes slightly pink. Then 25 mL of the neutral urine and 10 mL of the neutral solution of formaldehyde are mixed and titrated against decinormal sodium carbonate solution until a deep pink develops. Each mL of the decinormal sodium carbonate solution per 100 mL of urine corresponds to 0.017 g ammonia in 1000 mL of urine.