Dealloying is a well known phenomenon, but it is not always appreciated which alloys are susceptible to dezincification and which are not. Brasses containing up to ~15% zinc are single phase and do not dezincify in aggressive waters. Brasses containing 15 to ~37% zinc are single phase and will dezincify in aggressive waters, but this can be prevented by small additions of arsenic (usually 0.03 to 0.1%). Brasses containing more than ~37% zinc are two phase, or duplex brasses and these will dezincify in aggressive waters. Arsenic, or other, additions cannot inhibit the dezincification of two phase brasses, although the addition of ~1% tin, as found in naval brass, will slow it down.