or **AMONTUM**, the ancient name of the celebrated oasis (Siwah) on the west of Egypt, containing the oracle of the god Ammon. Arrian calls it a *place*, in which stood the temple of Jupiter Ammon, entirely surrounded by sandy wastes. Pliny states, that the oracle of Ammon was 12 days' journey from Memphis; and among the *Nomoi* of Egypt he reckons the *Nomos Ammoniacus*; Diodorus Siculus says that the district where the temple stood, though surrounded with deserts, was watered by dews which fell nowhere else in all that country. It was agreeably adorned with fruitful trees and springs, and full of villages. In the middle stood the Acropolis or citadel, encompassed with a triple wall; the first and innermost of which contained the palace; the others the apartments of the women, the household, and children, as also the temple of the god, and the sacred fountains for lustrations. Without the Acropolis stood, at no great distance, another temple of Ammon, shaded by a number of tall trees; near which there was a fountain, called that of the sun, or *Solis Fons*, because subject to extraordinary changes according to the time of the day; morning and evening warm, at noon cold, at midnight extremely hot. A kind of fossil salt was said to be naturally produced here. It was dug out of the earth in large oblong pieces, transparent as crystal. It was thought to be a present worthy of kings, and was used by the Egyptians in their sacrifices. From this our sal-ammoniac has taken its name. The observations of Brown and Hornemann prove that the oasis of Siwah is the district in which this celebrated oracle was situated. Pliny places it at 12 days' journey from Memphis, and Hornemann reached Siwah in 12 days from Cairo. These travellers found an old building 32 feet long, 15 broad, and 18 high, formed of large stones, and with some hieroglyphics upon it. This is most probably the ancient sanctuary of Ammon, which was placed in an enclosure, and surrounded by an outer wall. Near this old building is a spring, which still preserves, in popular opinion, the qualities attributed by the ancients to the Fountain of the Sun, and which, in fact, belong to all deep-seated cold springs. Our modern travellers found also the salt incrustations, the numerous date-trees, and the sea-shells and fossil wood in the neighbouring desert, which Strabo and other ancient writers notice. Arrian and Diodorus describe the district as having a breadth of 40 or 50 stadia, with which Brown's estimate of 4 to 6 English miles nearly agrees. Hornemann makes the circumference 50 miles, but he in- AMMONIAC, or Volatile Alkall. See Chemistry.