pure, but yellowish as usually sold; and it is easily known by the
peculiar appearance and odour of its fumes. A convenient additional
test, which, however, is not absolutely distinctive, is the formation of
white vapour when a rod dipped in it is brought near another dipped in
ammonia. If any farther evidence be desired, the strong acid must be
diluted with water, and examined by the tests for it in a diluted state.