1with the mouth and then a blue
flame will be emitted.
In the end the tubes
are weighed, and if their weights prove equal, he who has undertaken this work
has not laboured in vain. Lastly, both are placed in another balance-pan and
weighed; of each tube four grains must not be counted, on account of the
silver which remains in the gold and cannot be separated from it. From the
weight of the tubes we learn the weight both of the gold and of the silver
which is in the button. If some assayer has omitted to add so much silver to
the gold as to make it three times the quantity, but only double, or two and a
half times as much, he will require the stronger quality of aqua which
separates gold from silver, such as the fourth quality. Whether the aqua
which he employs for gold and silver is suitable for the purpose, or whether
it is more or less strong than is right, is recognised by its effect. That of
medium strength raises the little bubbles on the tubes and is found to colour
the ampulla and the operculum a strong red; the weaker one is found to
colour them a light red, and the stronger one to break the tubes. To pure
silver in which there is some portion of gold, nothing should be added when
they are being heated in the cupel prior to their being parted, except a bes
of lead and one-fourth or one-third its amount of copper of the lesser weights.
If the silver contains in itself a certain amount of copper, let it be weighed,
both after it has been melted with the lead, and after the gold has been parted
from it; by the former we learn how much copper is in it, by the latter how
much gold. Base metals are burnt up even to-day for the purpose of assay,
because to lose so little of the metal is small loss, but from a large mass of
base metal, the precious metal is always extracted, as I will explain in
Books X. and XI.
are weighed, and if their weights prove equal, he who has undertaken this work
has not laboured in vain. Lastly, both are placed in another balance-pan and
weighed; of each tube four grains must not be counted, on account of the
silver which remains in the gold and cannot be separated from it. From the
weight of the tubes we learn the weight both of the gold and of the silver
which is in the button. If some assayer has omitted to add so much silver to
the gold as to make it three times the quantity, but only double, or two and a
half times as much, he will require the stronger quality of aqua which
separates gold from silver, such as the fourth quality. Whether the aqua
which he employs for gold and silver is suitable for the purpose, or whether
it is more or less strong than is right, is recognised by its effect. That of
medium strength raises the little bubbles on the tubes and is found to colour
the ampulla and the operculum a strong red; the weaker one is found to
colour them a light red, and the stronger one to break the tubes. To pure
silver in which there is some portion of gold, nothing should be added when
they are being heated in the cupel prior to their being parted, except a bes
of lead and one-fourth or one-third its amount of copper of the lesser weights.
If the silver contains in itself a certain amount of copper, let it be weighed,
both after it has been melted with the lead, and after the gold has been parted
from it; by the former we learn how much copper is in it, by the latter how
much gold. Base metals are burnt up even to-day for the purpose of assay,
because to lose so little of the metal is small loss, but from a large mass of
base metal, the precious metal is always extracted, as I will explain in
Books X. and XI.
We assay an alloy of copper and silver in the following way.
From a
few cakes of copper the assayer cuts out portions, small samples from small
cakes, medium samples from medium cakes, and large samples from large
cakes; the small ones are equal in size to half a hazel nut, the large
ones do not exceed the size of half a chestnut, and those of medium size come
between the two. He cuts out the samples from the middle of the
bottom of each cake. He places the samples in a new, clean, triangular
crucible and fixes to them pieces of paper upon which are written the weight
of the cakes of copper, of whatever size they may be; for example, he writes,
“These samples have been cut from copper which weighs twenty centum
pondía.” When he wishes to know how much silver one centumpondíum of
copper of this kind has in it, first of all he throws glowing coals into the
iron hoop, then adds charcoal to it. When the fire has become hot, the paper
is taken out of the crucible and put aside, he then sets that crucible on the
fire and gradually heats it for a quarter of an hour until it becomes red hot.
Then he stimulates the fire by blowing with a blast from the double bellows
for half an hour, because copper which is devoid of lead requires this time to
become hot and to melt; copper not devoid of lead melts quicker. When
he has blown the bellows for about the space of time stated, he removes the
glowing charcoal with the tongs, and stirs the copper with a splinter of wood,
which he grasps with the tongs. If it does not stir easily, it is a sign that the
few cakes of copper the assayer cuts out portions, small samples from small
cakes, medium samples from medium cakes, and large samples from large
cakes; the small ones are equal in size to half a hazel nut, the large
ones do not exceed the size of half a chestnut, and those of medium size come
between the two. He cuts out the samples from the middle of the
bottom of each cake. He places the samples in a new, clean, triangular
crucible and fixes to them pieces of paper upon which are written the weight
of the cakes of copper, of whatever size they may be; for example, he writes,
“These samples have been cut from copper which weighs twenty centum
pondía.” When he wishes to know how much silver one centumpondíum of
copper of this kind has in it, first of all he throws glowing coals into the
iron hoop, then adds charcoal to it. When the fire has become hot, the paper
is taken out of the crucible and put aside, he then sets that crucible on the
fire and gradually heats it for a quarter of an hour until it becomes red hot.
Then he stimulates the fire by blowing with a blast from the double bellows
for half an hour, because copper which is devoid of lead requires this time to
become hot and to melt; copper not devoid of lead melts quicker. When
he has blown the bellows for about the space of time stated, he removes the
glowing charcoal with the tongs, and stirs the copper with a splinter of wood,
which he grasps with the tongs. If it does not stir easily, it is a sign that the