These two things are done simultaneously by heating and melting the ore in contact with coke, charcoal or anthracite, in the iron blast furnace, from which issue intermittently two molten streams, the iron now deoxidized and incidentally carburized by the fuel with which it has been in contact, and the mineral matter, now called " slag."
Until 644 the island was exceedingly prosperous, but in that year began the period of Arab invasions, which continued intermittently until 975.
The whole system is volcanic, and a considerable number of volcanoes are still intermittently active, noticeably in central and southern Chile.
In April 1865 an Indian war broke out under the leadership of Blackhawk, which lasted intermittently until the end of 1867.
On the introduction of the Waterworks Clauses Act 1847, an impetus was given to high-pressure supplies, and the same systems of distributing mains were frequently employed for the purpose; but with few exceptions the water continued to be supplied intermittently, and cisterns or tanks were necessary to store it for use during the periods of intermission.