Steaming potatoes

Put them clean-washed, with their skins on, into a steam saucepan, and let The water under them be about half boiling; let them continue to boil rather quickly, until they are done. If the water once relaxes from its heat the potato is sure to be affected, and to become soddened, let the quality be ever so good. A too precipitate boiling is equally disadvantageous, as the higher parts to the surface of the root begin to crack and open while the centre part continues unheated and undecomposed.

see Wikipedia Cookbook