Bog Iron
This is an Earth Cache. There is no CC at the location. What is there, is a place to examine and answer some questions in your log. THIS IS A CONSERVATION AREA SO YOU CAN NOT DISTURB ANYTHING OR DIG FOR BOG IRON.
Bog iron was the first iron used to make tools and weapons. The iron is formed by the action of iron oxidizing bacteria (Thiobacillus ferrooxidans and Leptospirillum ferrooxidans) in a bog area.
The requirements are water with dissolved iron, an acid environment, an anaerobic (deoxygenated) environment for microorganisms feeding on decaying organic matter, proper temperature range, and another environment where there is exposure to a sufficient level of oxygen to oxidize the dissolved iron. Often these two environments are as layers.
We have dissolved iron in this area as seen in the rust stains on sinks, toilets, and sides of houses near spigots. We also have the acid swamps (bogs), with decaying matter, on the property. This property was once called the “Pine Swamp”. Some water is brought in by Chartley Brook, some by seepage, and some from rain runoff. The spongy area on the trail just past the boardwalk is sphagnum moss which decays very slowly and creates the acid environment necessary for the bacteria.
The microorganisms feeding on the decaying organic matter (leaves, wood, pine needles, dead animals, etc.) obtain oxygen in the anaerobic (no oxygen) zone by combining insoluble (cannot be dissolved in water) ferric oxide (rust) in the soil with water to form soluble ferrous hydroxide. The microorganisms also are producing acid which also dissolves the ferric oxide.
4H2O + 2Fe2O3 → 4Fe(OH)2 + O2
(water) + (Iron[III] oxide) → (Iron[II] hydroxide) + (oxygen)
Then the iron oxidizing bacteria, living in an area with some oxygen (aerobic), then takes the dissolved ferrous hydroxide and combines it with the oxygen and converts it back to ferric oxide which it forms in combination with silicates into clumps. Sand is a silicate. It takes about 20 years to make pea sized clumps. Left to go longer, they can form large rocks of several pounds.
4Fe(OH)2 + O2 → 4H2O + 2Fe2O3
(Iron[II] hydroxide) + (oxygen) → (water) + (Iron[III] oxide)
A byproduct of the iron oxidizing bacteria can be a sheen left on the water which is an oxide of manganese and iron. This is a sign that the bacteria are active and is mainly visible in warmer months but when there is water present. There may be little sign when the area is dried up.
The colonists in this area would prospect and dig up these iron deposits from the bogs and process them into iron in bloomery furnaces.
First, they would roast the bog iron on a wood fire. This would remove some of the silicates and any water in the clumps. Next, they would break up the lumps into a powder. If they had a magnet they would use it to separate the ferrous (iron bearing) particles from the impurities. Otherwise they would just have to use the powder with impurities.
They would build a bloomery furnace out of bricks and clay. They would let it dry to prevent it from exploding from steam when it was fired. A fire would be started in the furnace and the bog iron powder would be loaded into the furnace in alternating layers with charcoal. It took about 4.5 pounds of charcoal for every pound of bog iron. Since charcoal is so light, that means they used a considerable amount of charcoal. They would have to use a bellows to continually put air into the furnace from the bottom.
Normally it would take 8 to 12 hours to get the bog iron to form a bloom of iron. The temperature never got hot enough to melt the iron but rather just combined and consolidated it. Imagine pumping a large bellows for 8 – 12 hours.
The furnace then had to be broken apart to get the white hot consolidated “bloom” out of the furnace. The bloom was then pounded with hammers to squeeze out as much slag (impurities, mostly silicates) as possible while it was still hot. This was another tedious process. In some areas, such as Palmer River and Taunton, they had a water powered mill to power the hammering.
Since there was still some slag left in the iron, this iron was not of the purest quality and had a certain brittleness. It could only be used for certain products. Later with the advent of coal being found, the iron could be melted at a higher temperature and further purified producing “pig” iron. There is actually coal in this area and there were mines in Plainville and Cranston.
Only about a mile from here is Iron Mine Creek on Tremont Street in Rehoboth. This was an active bog iron mining area. The large cranberry bog there and many others in the area were actually bog iron mines first. There were bloomery furnace operations at Palmer River in Rehoboth, in Norton, and several areas in Taunton. Iron was so valuable that it was often used as wages. Local ministers often would get half their pay in iron bars.
Even though there is no information that bog iron was mined on this property, there are indications of bog iron being here.
Answer these questions in your log. To answer these questions, you will be looking along the boardwalk.:
What color was the wet soil?
Did you see any rust colored areas?
Did you see any oily patches? If so, what size?
References:
Wikipedia
Betsey Dexter Dyer Ph.D.