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Book VII marbles, gems in rings and other applications

Book VII marbles, gems in rings and other applications Page of 251 Book VII marbles, gems in rings and other applications Text size:minus plus Restore normal size   Mail page  Print this page
BOOK VII
163
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
Book VII marbles, gems in rings and other applications Page of 251 Book VII marbles, gems in rings and other applications
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