CLEVELAND WAY EARTHCACHE 4: ALUM WORKING AT BOULBY EarthCache
CLEVELAND WAY EARTHCACHE 4: ALUM WORKING AT BOULBY
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One of a series of Earthcaches that can be completed by Geocachers walking the 110 mile Cleveland Way, without straying far from the path.
Most of the cliffs between the villages Skinningrove and Sandsend bear the scars of Alum working and during the 18th and 19th centuries
North Yorkshire was the main producer of this chemical in Britain.
The Earthcache is placed at Boulby because the cliffs here are the highest on the east coast of England (666 feet high) and there is also an information panel nearby which gives information about the view, although this is becoming faded due to sunlight.
In the early 17th century the mineral alum was discovered in the Upper Lias Shales of the Jurassic layers deposits in North Yorkshire. Alum was first quarried at Boulby in the 1650’s and, by 1851, the present site was employing 355 people, 314 of whom were labouring digging the shale.
Alum consists of aluminium sulphate and an alkaline sulphate. In Yorkshire the alkali part had to be added by treatment either with ammonia (from urine collected locally or imported from London) or potassium (from potash or potassium chloride). The Yorkshire product was a mixture of both kinds of alum.
The process started with the quarrying of the shale which was then ‘calcined’. This involved it being piled into mounds (or clamps) up to 30 metres (90 feet) high on top of a bed of brushwood, which was set alight. Large retaining walls, which helped form the bases of the calcining clamps, are still visible on the cliff below you. The clamps would burn slowly for up to a year and then the burned shale would be put in shallow tanks for ‘leaching’. This involved covering the calcined shale with water and some ‘mother liquour’ and boiling it until two thirds of the water was removed. Then the source of ammonia or potassium was added and the liquid cooled to produce alum crystals. The excess liquid (mother liquor) was recycled into the leaching tanks. Finally the alum was purified by washing the crystals with cold water (or mother liquor) then redissolving them in hot water before finally cooling to allow recrystallization.
At Boulby the liquor flowed along a culvert and some tunnels in the cliff to the Alum house over a mile away where the processing to produce crystals was carried out. An artificial harbour was constructed for the ships that brought in the coal, potash and urine and removed the alum.
The industry in North Yorkshire collapsed when a technique was developed to produce alum from colliery waste treated with sulphuric acid, but Boulby was one of the last works to close in 1871.
To log this Earthcache use the information on the panel to tell me by e-mail :-
1) How many leaching tanks are there the remains of near the cliff edge?
2) What the black cone at the south end of the site is the remains of ?
and
3) Three possible uses for the alum produced in 19th century Britain.
Additional Hints
(No hints available.)