Book III about halite and nitrium, alum and acrid juices and related minerals, sulphur, bitumen, realgar, and orpiment; the fourth, chrysocolla, aerugo, caeruleum, ferrugo

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	42	DE NATURA FOSSILIUM

	in oblong plates similar in appearance to gypsum and decrepitates in fire. So much regarding salt. We shall now consider nitrum which is related to salt.⁶ It is found in nature and is produced artificially similar to salt. Nitrum is found within the earth and on the surface. When found in the earth it is dug out like other salts and is hard and dense, similar to stone. The Venetians make chrysocolla, the material I call borax, from this mineral.⁷ Sometimes it is collected from caves where it either hangs down from the roof like icicles or it forms on the floor of the cave from water that drips from the roof. It is soft, incoherent, and white with the appearance of foam. The Greeks call it aphronitrum not so much because it is found in the earth as because it occurs in caves and only the soft, foam-like material is so-named. The dense, hard mineral is not true aphronitrum. The Greeks indentified these minerals on the basis of quality and uniformity. Nitrum is mined or collected in Asia, especially at Alashehr, Lydia, and Manissa, Caria. It is interesting to note that Emperor Gallienus, when he was informed by dispatches and messengers that Asia was to be devastated by the Scythians, exclaimed, with a certain jocular license, "What! We cannot five without aphronitrum." Nitrum is found on the surface of the earth in protected valleys and on flat plains or in lakes. When it occurs as an efflorescence on the surface the Greeks call it halmirhaga, a name derived in part from its rather salty taste, in part because it comes up out of the earth. Pliny mentions that the valleys along the Media river become white during the summer and it would appear that the entire surface of the ground around Philippopolis, Thrace, is impregnated with the mineral. Pliny calls the earth of these fields "filthy." A lake in eastern Macedonia in the Letaeus district produces this mineral. The mineral called chalastraeum by the old writers came from a bay near the town of Chalastra, whence the name. There are many varieties of artificial nitrum. One variety is made in Egypt from the alkali water of the Nile which is conducted to the plants. These are situated at Naucratis, Nitria, and Memphis. In these plants, as in salt works, the finest and lightest froth may be called "flowers of nitrum" but it is more commonly called "nitrum foam." The Greeks call this material by two separate names, αφρός νίτρου, in order to distinguish it from the natural mineral which is similar to foam and which they call άφρόητροϊ. Dioscorides calls both aphronitrum and "nitrum foam," αφρός νίτρου. He distinguishes one from the other by quality and writes that the finest material comes from Lydia and that this is aphronitrum while the second quality mineral, "nitrum foam," comes from Egypt. Some artifi- • Until the latter part of the 16th century, there was confusion in the use of the name nitrum (Greek, νίτρο»). In general it included all hydrous sodium carbonates, natron, thermonatrite, trona, etc., as well as other minerals obtained from soda lakes, especially those in Egypt and Asia. ⁷ Natron, Na₂C0₃ · 10H₂O, borax, Na₂B₄0₇ · 10H₂O.

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