Agricola, Georgius, De re metallica, 1912/1950

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              the vessels and vats is again poured back into the caldron to be re-boiled.
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              <s>The earth which settled at the bottom of the caldron is carried back to the
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              tanks, and, together with the ore, is again dissolved with water and urine.
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              <s>The earth which remains in the tanks after the solution has been drawn off
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              is emptied in a heap, and daily becomes more and more aluminous in the
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              same way as the earth from which saltpetre was made, but fuller of its juices,
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              wherefore it is again thrown into the tanks and percolated by water.</s>
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              <s>Aluminous rock is first roasted in a furnace similar to a lime kiln. </s>
              <s>At
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              the bottom of the kiln a vaulted fireplace is made of the same kind of rock;
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              the remainder of the empty part of the kiln is then entirely filled with the
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              same aluminous rocks. </s>
              <s>Then they are heated with fire until they are red
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              hot and have exhaled their sulphurous fumes, which occurs, according to their
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              divers nature, within the space of ten, eleven, twelve, or more hours. </s>
              <s>One
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              thing the master must guard against most of all is not to roast the rock
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              either too much or too little, for on the one hand they would not soften when
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              sprinkled with water, and on the other they either would be too hard or
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              would crumble into ashes; from neither would much alum be obtained, for
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              the strength which they have would be decreased. </s>
              <s>When the rocks are cooled
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              they are drawn out and conveyed into an open space, where they are piled one
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              upon the other in heaps fifty feet long, eight feet wide, and four feet high,
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              which are sprinkled for forty days with water carried in deep ladles. </s>
              <s>In
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              spring the sprinkling is done both morning and evening, and in summer at </s>
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