Page:Encyclopædia Britannica, Ninth Edition, v. 1.djvu/786

Society a correct detail of the whole process, which he had received from Dr Hasselquist, who had travelled in that country as a naturalist. This account is published in the 51st volume of the Philosophical Transactions, 1760, p. 504. Almost the only fuel used in Egypt is the dung of cattle. The dung of black cattle, horses, sheep, goats, <fec., which contains the sal-ammoniac ready formed, is collected during the first four months of the year, when the animals feed on the spring grass, a kind of clover. It is dried, and sold to the common people as fuel. The soot from this fuel is carefully collected and sold to the sal-ammoniac makers, who work only during the months of March and April, for it is only at that season of the year that the dung is fit for their purpose.

The composition of this salt seems to have been first discovered by Tournefort in 1700. The experiments of the younger Geoffroy in 1716 and 1723 were still more decisive, and those of Duhamel, in 1735, left no doubt upon the subject. Dr Thomson first pointed out a process by synthesis, which has the advantage of being very simple, and at the same time rigidly accurate, resulting from his observation that when muriatic gas and ammoniacal gas, both as dry as possible, are brought in contact with each other, they always combine in equal volumes.

The first attempt to manufacture sal-ammoniac in Europe was made, about the beginning of the 18th cen tury, by Mr Goodwin, a chemist of London, who appears to have used the mother ley of common salt and putrid urine as ingredients. The first successful manufacture of sal- ammoniac in this country was established in Edinburgh by Dr Hutton and Mr Davy, about the year 1760. It was first manufactured in France about the same time by Baume . Manufactories of it were afterwards established in Germany, Holland, and Flanders.

Chloride of ammonia is now manufactured in large quan tity from the crude carbonate of ammonia obtained in gas works, or from the destructive distillation of animal matter. This salt is changed into chloride by the addition of hydrochloric acid or the mother liquor of salt-works, called bittern, containing the chlorides of calcium and magnesium. When hydrochloric acid is not easily got for neutralisation, the crude gas liquor is transformed into sulphate, and this is mixed with an equivalent quantity of common salt. During the subsequent evaporation the sulphate of soda separates in hard granular crystals, which are apt to adhere to the sides of the boiler. The liquor is agitated to prevent this adhesion taking place, and assist in the separation of the sulphate of soda. The sulphate of soda is removed by drainers as it is formed, and the mother liquor boiled up to the crystallising point, and run off into coolers. The crystals of impure muriate of am monia are dried carefully and subsequently sublimed.

Sal-ammoniac occurs usually in the form of a hard, white cake, opaque, or only slightly translucent. Its taste is cooling, saline, and rather disagreeable. It dissolves in 272 parts of water at 18 7 C. with great reduction of tem perature, and in about an equal weight of water at the boiling-point. The feathery crystals it forms are found on microscopic examination -to be masses of cubes or octahedrons; their specific gravity is about 1 5. When exposed to a moist atmosphere, the salt gradually absorbs water, and deliquesces, though very slowly, becoming slightly acid. When heated, it sublimes unaltered in a white smoke, having a peculiar smell, very characteristic of sal-ammoniac. If a cold body be presented to this smoke, the sal-ammoniac condenses on it, and forms a white crust. When thus sublimed, it has the property of carrying along with it various bodies, which, when heated by themselves, are perfectly fixed.

For the other ammoniacal salts see Chemistry.

AMMONIACUM, or Ammoniac, a gum-resinous exuda tion from the stem of a perennial herb (Dorema ammonia- cum) belonging to the natural order Umbelliferse. The- plant grows to the height of 8 or 9 feet, and its whole stem is pervaded with a milky juice, which oozes out on an incision being made at any part. This juice quickly hardens into round tears, forming the "tear ammonia- cum " of commerce. Lump ammoniacum, the other form in which the substance is imported, consists of aggrega tions of tears, frequently incorporating large quantities of the fruits of the plant itself, as well as other foreign bodies. In order to free lump ammoniacum from these impurities, it has to be melted and strained, operations which depre ciate its therapeutical value. Ammoniacum has a faintly foetid unpleasant odour, which becomes more distinct on heating ; externally it possesses a reddish yellow appear ance, and when the tears or lumps are freshly fractured they exhibit an opalescent lustre. It is chiefly collected in the province of Irak in Persia ; but some quantity is also produced in the Punjab, and comes to the European market by way of Bombay. Its composition, according to Hagen, is resin, 68 6; gum, 19 3; gluten, 5 4; volatile* oil and water, 2 8; extractive, &c., 3 9. Ammoniacum is closely related to assafoetida, not only in the plant yielding it, but also in its therapeutical effects. It may be used aa a substitute for assafoetida, although, containing a much smaller proportion of volatile oil, its effect is less powerful. Internally it is used in conjunction with squills in bronchial affections ; and in asthma and chronic colds it is found useful. It is, however, more used externally in the form of plasters, as a discutient or resolvent application in indo lent tumours, affections of the joints, &c.

African ammoniacum is a totally different substance, though often confounded with the real gum-resin, which is produced only in the East. It is the product of an un known plant growing in North Africa, and occasionally shipped to our markets from Marocco. It is a dark- coloured gum-resin, possessed of a very weak odour and a persistent acrid taste. A considerable commerce in it is carried on between Mogador and Alexandria, where it is in demand for purposes of fumigation.

AMMONITES, called also very frequently the children of Ammon, a people allied by descent to the Israelites, and living in their vicinity, sprung from Lot, Abraham’s nephew, by the younger of his daughters, as the immediately adjoining people, the Moabites, were by the elder (Gen. xix. 37–38). Both peoples are sometimes spoken of under the common name of the children of Lot (Deut. ii. 19; Ps. lxxxiii. 8); and the whole history shows that they preserved throughout the course of their national existence a sense of the closest brotherhood. The original territory of the two tribes was the country lying immediately on the east of the Dead Sea and of the lower half of the Jordan, having the Jabbok for its northern boundary; and of this tract the Ammonites laid claim to the northern portion, the “half mount Gilead” (Deut. iii. 12), lying between the Arnon and the Jabbok, out of which they had expelled the Zamzummim (Judg. xi. 13; Deut. ii. 20, 21; cf. Gen. xiv. 5), though apparently it had been held, in part at least, conjointly with the Moabites, or perhaps under their supremacy (Num. xxi. 26, xxii. 1; Josh. xiii. 32). From this their original territory they had been in their turn expelled by the Amorites, who were found by the Israelites after their deliverance from Egypt in possession of both Gilead and Bashan, that is, of the whole country on the left bank of the Jordan, lying to the north of the Arnon (Num. xxi. 13). By this Amorite invasion, as the Moabites were driven to the south of the Arnon, which formed their northern boundary from that time so the Ammonites wore driven out of Gilead