Federalism in the idea of the power being shared between the national and state level. checks and balances to keep the government from becoming tyrannical.
The Bessemer Process was the first inexpensive industrial process for the mass-production of steel from molten pig iron prior to the open hearth furnace. The key principle is the removal of impurities from the iron by oxidation by blowing air through the molten iron.
Barter does not involve money