1the vessels and vats is again poured back into
the caldron to be re-boiled.
The earth which settled at the bottom of the caldron is carried back to the
tanks, and, together with the ore, is again dissolved with water and urine.
The earth which remains in the tanks after the solution has been drawn off
is emptied in a heap, and daily becomes more and more aluminous in the
same way as the earth from which saltpetre was made, but fuller of its juices,
wherefore it is again thrown into the tanks and percolated by water.
The earth which settled at the bottom of the caldron is carried back to the
tanks, and, together with the ore, is again dissolved with water and urine.
The earth which remains in the tanks after the solution has been drawn off
is emptied in a heap, and daily becomes more and more aluminous in the
same way as the earth from which saltpetre was made, but fuller of its juices,
wherefore it is again thrown into the tanks and percolated by water.
Aluminous rock is first roasted in a furnace similar to a lime kiln.
At
the bottom of the kiln a vaulted fireplace is made of the same kind of rock;
the remainder of the empty part of the kiln is then entirely filled with the
same aluminous rocks. Then they are heated with fire until they are red
hot and have exhaled their sulphurous fumes, which occurs, according to their
divers nature, within the space of ten, eleven, twelve, or more hours. One
thing the master must guard against most of all is not to roast the rock
either too much or too little, for on the one hand they would not soften when
sprinkled with water, and on the other they either would be too hard or
would crumble into ashes; from neither would much alum be obtained, for
the strength which they have would be decreased. When the rocks are cooled
they are drawn out and conveyed into an open space, where they are piled one
upon the other in heaps fifty feet long, eight feet wide, and four feet high,
which are sprinkled for forty days with water carried in deep ladles. In
spring the sprinkling is done both morning and evening, and in summer at
the bottom of the kiln a vaulted fireplace is made of the same kind of rock;
the remainder of the empty part of the kiln is then entirely filled with the
same aluminous rocks. Then they are heated with fire until they are red
hot and have exhaled their sulphurous fumes, which occurs, according to their
divers nature, within the space of ten, eleven, twelve, or more hours. One
thing the master must guard against most of all is not to roast the rock
either too much or too little, for on the one hand they would not soften when
sprinkled with water, and on the other they either would be too hard or
would crumble into ashes; from neither would much alum be obtained, for
the strength which they have would be decreased. When the rocks are cooled
they are drawn out and conveyed into an open space, where they are piled one
upon the other in heaps fifty feet long, eight feet wide, and four feet high,
which are sprinkled for forty days with water carried in deep ladles. In
spring the sprinkling is done both morning and evening, and in summer at
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