Leaks are detected (in small amounts of ammonia) when a lit sulfur candle is used. The candle will give off a very thick, white smoke when it contacts the ammonia leak. The use of phenolphthalein paper is also considered a good test. The smallest trace of ammonia will cause the moistened paper strip to turn pink. A large ammonia will cause the phenolphthalein paper to turn a vivid scarlet.