I was walking down the side of Coniston Water when I found rocks like these on the shore line. I knew that there had been iron furnaces in the area centuries ago and I knew that they were called bloomeries. I looked it up and found out that they were homemade heaps of charcoal carbon and iron ore insulated to get hot enough. It is a form of smelting and works because the carbon burns in limited oxygen and produces carbon monoxide. This is hungry for oxygen which it then steals from the iron oxide in the rock. The iron oxide is reduced to iron. Carbon dioxide is made and goes into the air. The iron and the rocky remains of the ore form a molten slag at the bottom which hardens into this slag seen below.
I wondered at first if it was actually iron, so we tested it with a magnet. It didn't stick so no evidence for iron there. I then set out to measure the density.
I weighed the rocks and then put them into a displacement can. I measured the volume of the water displaced.
The bigger rock was 507 grams and 200 cubic centimetres. Density = 2.5 grams per cubic cm. The smaller rock 285 grams and 120 cubic centimetres. Density = 2.4 grams per cubic cm. Iron itself has a density of 7.8 grams per cubic cm so if there is any iron here, there's clearly not much. Apparently the slag was then reheated to get the iron. This produced wrought iron.
