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BOOK VII
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163
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tuousness
but is always unctuous. Only the pure true material is of any value
since the mixed material is full of impurities. They make white lime
from the pure varieties and the whitest rock is found near Bruno. Dark
lime is made from dark "calcareous" rocks and varicolored lime from
varicolored varieties. The white lime is given preference if it is of
good quality otherwise. Neither the whitewashers nor plasterers find
the dark lime suited to their needs. Lime from soft rock is more useful
to plasterers and that from hard rock more useful to builders. Lime
from unctuous rocks is more tenaceous than that from meager while that
from loose-textured and porous varieties is lighter than that from
dense. In each case the first named lime is more suited to the needs of
plasterers, the latter to construction. It can be obtained from rocks
suitable for millstones, not the sandstones but the unctuous rocks.
The lime from siliceous rocks is not good because a large part of the
rock goes into a glassy slag when burnt. Better lime is made from the
shells of marine mollusks. The fire in burnt lime is so concealed that
when it cools it appears to be cold yet this fire is rapidly aroused
with water. For this reason it is usually reduced to the very finest
powders.
Lime
is used in a great many ways. It is used in preparing olive oil and on
vines. The Hedui and Pictores fertilize their fields with it. Certain
African peoples treat wine with it in order to neutralize the sharp
taste. It is collected by the living from arched vaults and mixed with
water so that a cadaver thrown into it may be entirely consumed. Dyers,
tanners and medical men use it but they require fresh lime that has not
been slacked. It burns so violently that it forms thin crusts. In a
short time after it dries it will not burn further but still is capable
of warming and drying the flesh and even eating it away. After it has
been washed three or four times it will not bite but will dry
effectively. However, the principal use is in constructing buildings.
According to Vitruvius if the sand with which it is mixed is natural or
pit sand the proportions are three of sand to one of lime; if fluvial
or marine, two to one. These are the best proportions. If a third part
of shells, tufa or impure chalk, is added to fluvial or marine sand a
better mixture is obtained. A better mortar is obtained if the lime and
sand are mixed together and allowed to stand for a period of three
years. Certain buildings are not firm and stable because the mortar was
prepared too soon after mixing the lime and sand.
Lime is used in making the maltha the
Romans used to cement their aqueducts, castles and reservoirs.
According to Pliny this material was extremely tenacious and had a
hardness equal to that of the rocks mentioned above. It can be seen in
Rome today. The name is derived from maltha, a genus of
bitumen. The natural material will produce the firmest of Avails and
the artificial cement is used in the same manner. The latter is used to
plug cracks in aqueducts and reservoirs since it is as tenacious as
natural bitumen. The older writers have described two genera of the
artificial cement, each being made of lime and lard. The sap of the
fig tree is
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