This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do", by Popular Mechanics Co.. Also available from Amazon: The Boy Mechanic, Vol2: 1000 Things for Boys to Do.
A good way to clean glass vessels in which hard water is boiled is to use the following mixture to remove Not only the calcium deposits, but also rust or sulphur stains that may be present. The solution is a mixture of ammonia water and a few ounces of salt. This should be placed in the glass vessel and boiled until the deposits disappear. The ammonia water may be made of any strength by diluting if necessary.