and Southern Nubia, producing an inferior brownish gum of the same description as the preceding.

4. A. arabica Willd. (A. vera Willd., A. nilotica Delile). This tree under the form described by Delile as A. nilotica, distinguished by having the legumes glabrous instead of tomentose, is largely planted in the valley of the Nile throughout the whole of Egypt and Nubia, where it is known by the name of Sont. On the banks of the White and Blue Nile and in Southern Nubia, it occurs in primæval forests. Schweinfurth, who regards it as a distinct species, states that it affords a very scanty amount of gum, which though collected for use in the country, is nowhere an article of trade.

The tree is widely distributed in Africa, occurring on the west side from Senegambia and the Niger to Angola; and on the east from the valley of the Nile to Abyssinia, Mozambique and Natal.1 It is supposed to be the source of the gum exported from Fezzan and Morocco.

A. arabica is the Kikar of the Punjab, the Babul or Babur of Central India. Cultivated or self-sown, it is found throughout the greater part of the peninsula, excepting the most humid coast-regions, and the extreme north-west beyond the Jhelam, where the winter frost is too severe. In some districts of Sindh and Guzerat where it forms entire forests, the tree supports the lac-insect. Gum is abundantly exuded from its bark, and with that of other trees, forms a portion of the East India Gum Arabic of commerce.2

5. A. horrida Willd. (A. Capensis Burch.) a large tree, the Doornboom, Wittedoorn or Karródoorn of the Cape colonists, is the well-ascertained source of the chief portion of the South African gum arabic. It is the commonest tree of the lonely deserts of South Africa.

A. pycnantha Benth.; A. decurrens Willd. (A. mollissima Willd.), the Black or Green Wattle-tree of the colonists; A. dealbata Link, the Silver Wattle; and A. homalophylla A. Cunn., are the trees which furnish the gum arabic of Australia.3

History-The history of this drug carries us back to a remote antiquity. The Egytian fleets brought gum from Arabia as early as the 17th century B.C. Thus in the treasury of king Rhampsinit (Ramses III.) at Medinet Abu, there are representations of gum-trees, together with heaps of gum. The symbol used to signify gum, is read Kami-en-punt. i.e. gum from Arabia, and is of frequent occurrence in Egyptian inscriptions; sometimes mention is made of gum from Canaan. The word kami is the original of the Greek κóuμ, whence through the Latin our own word gum.*

The Egyptians used gum largely in painting: an inscription exists which states that in one particular instance a solution of kami (gum) was used to render adherent the mineral pigment called chesteb,5 the name applied to lapis lazuli or to a glass coloured blue by cobalt.

1 As var. B. Kraussiana Benth.-Harvey and Sonder, Flor. Capens. ii. (1861-2) 281. 2 Brandis, Forest Flora of North-Western and Central India, Lond. 1874. 181.-It must however be borne in mind that a large proportion of the gum shipped from Bombay is the produce of Eastern Africa.

s Victorian Exhibition, 1861.-Report on Class 3. (Indigenous Vegetable Substances), Melbourne, 1862, 58.

We have to thank Professor Dümichen for most of the information relating to Egypt, which may be partly found in his own works, and partly in those of Brugsch, Ebers, and Lepsius.

5 Lepsius, Abhandl. der Akademie der Wissensch. zu Berlin for 1871, p. 77. 126. Metalle in den Aegyptischen Inschriften.

Turning to the Greeks, we find that Theophrastus in the 3rd and 4th century B.C. mentioned Kópμe as a product of the Egyptian "Aκavba, of which tree there was a forest in the Thebaïs, of Upper Egypt. Strabo also, in describing the district of Arsinöe, the modern Fayûm, says that gum is got from the forest of the Thebaïc akanthe.

Celsus in the 1st century mentions Gummi acanthinum; Dioscorides and Pliny also describe Egyptian gum, which the latter values at 3 denarii [2s.] per lb.

Gum was employed by the Arabian physicians and by those of the school of Salerno, yet its utility in medicine was but little appreciated, and its value in the arts quite ignored until a much later period. During the middle ages, the small supplies that reached Europe were procured through the Italian traders, from Egypt and Turkey. Thus Pegolotti1 who wrote a work on commerce about A.D. 1340, speaks of gum arabic as one of the drugs sold at Constantinople by the pound, not by the quintal. Again in a list of drugs liable to duty at Pisa in 1305,2 and in a similar list relating to Paris in 1349,3 we find mention of gum arabic, It is likewise named by Pasi, in 1521, as an export from Venice to London.

Gum also reached Europe from Western Africa, with which region the Portuguese had a direct trade as early as 1449.

Production-Respecting the origin of gum in the tribe Acacica, no observations have been made similar to those of H. von Mohl on tragacanth.

It appears that gum generally exudes from the trees spontaneously, in sufficient abundance to render wounding the bark superfluous. The Somali tribes of East Africa however, are in the habit of promoting the outflow by making long incisions in the stem and branches of the tree.5 In Kordofan the lumps of gum are broken off with an axe, and collected in baskets.

The most valued product called Hashabi gum, from the province of Dejara in Kordofan, is sent northward from Bara and El Obeid to Dabbeh on the Nile, and thence down the river to Egypt; or it reaches the White Nile at Mandjara.

A less valuable gum known as Hashabi el Jesire, comes from Sennaar on the Blue Nile; and a still worse from the barren table-land of Takka, lying between the eastern tributaries of the Blue Nile and the Atbara and Mareb; and from the highlands of the Bisharrin Arabs between Khartum and the Red Sea. This gum is transported by way of Khartum or El Mekheir (Berber), or by Suakin on the Red Sea. Hence, the worst kind of gum is known in Egypt as Samagh Savakumi (Suakin Gum).

According to Munzinger, a better sort of gum is produced along the Samhara coast towards Berbera, and is shipped at Massowa. Some of it reaches Egypt by way of Jidda, which town being in the district of Arabia called the Hejaz, the gum thence brought receives the name of Samagh Hejazi; it is also called Jiddah or Gedda Gum. The gums of

Zeila, Berbera and the Somali country about Gardafui, are shipped to Aden, or direct to Bombay. A little gum is collected in Southern Arabia, but the quantity is said to be insignificant.1

In the French colony of Senegal, gum, which is one of its principal productions, is collected chiefly in the country lying north of the river, by the Moors who exchange it for European commodities. The gathering commences after the rainy season in November when the wind begins to set from the desert, and continues till the month of July. The gum is shipped for the most part to Bordeaux. The quantity imported into France in 1870 from Senegal, was 2,862,669 kilo. (107,116 cwt.), value 5,439,076 francs 2 (£217,563).

Description-Gum arabic does not exhibit any very characteristic forms like those observable in gum tragacanth. The finest white gum. of Kordofan, which is that most suitable for medicinal use, occurs in lumps of various sizes from that of a walnut downwards. They are mostly of ovoid or spherical form, rarely vermicular, with the surface in the unbroken masses, rounded, in the fragments, angular. They are traversed by numerous fissures, and break easily and with a vitreous fracture. The interior is often less fissured than the outer portion. At 100° C. the cracks increase, and the gum becomes extremely friable. In moist air, it slowly absorbs about 6 per cent. of water.

The finest gum arabic is perfectly clear and colourless; inferior kinds have a brownish, reddish or yellowish tint of greater or less intensity, and are more or less contaminated with accidental impurities such as bark. The finest white gum turns black and assumes an empyreumatic taste, when it is kept for months at a temperature of about 98° C., either in an open vessel, or enclosed in a glass tube, after having been previously dried over sulphuric acid or not.

An aqueous solution of gum deviates the plane of polarization 5° to the left in a column 50 mm. long; but after being long kept, it becomes strongly acid, the gum having been partly converted into sugar, and its optical properties are altered. An alkaline solution of cupric tartrate is not reduced by solution of gum even at a boiling heat, unless it contains a somewhat considerable proportion of sugar, extractable by alcohol, or a fraudulent admixture of dextrin.

We found the sp. gr. of the purest pieces of colourless gum dried in the air at 15° C., to be 1487; but it increases to 1.525, if the gum is dried at 100°.

The foregoing remarks apply chiefly to the fine white gum of Kordofan, the Picked Turkey Gum or White Sennaar Gum of druggists. The other sorts which are met with in the London market are the following:—

1. Senegal Gum-As stated above, this gum is an important item of the French trade with Africa, but it is not much used in England. Its colour is usually yellowish or somewhat reddish, and the lumps, which are of large size, are often elongated or vermicular. Moreover Senegal gum never exhibits the numerous fissures seen in Kordofan gum, so that the masses are much firmer and less easily broken. In every other respect, whether chemical or optical, we find Senegal gum

3

3 Flückiger, in the Jahresbericht of Wiggers and Husemann, 1869. 149.

Р

and Kordofan gum to be identical; and the two, notwithstanding their different appearance, are produced by one and the same species of Acacia, namely Acacia Verek.

2. Suakin Gum, Talca or Talha Gum, yielded by Acacia stenocarpa, the Talch or Talha of the Arabs, and by A. Seyal var. Fistula, is remarkable for its brittleness, which occasions much of it to arrive in the market in a semi-pulverulent state. It is a mixture of nearly colourless and of brownish gum, with here and there pieces of a deep reddishbrown. Large tears have a dull opaque look, by reason of the innumerable minute fissures which penetrate the rather bubbly mass. It is imported from Alexandria.

3. Morocco, Mogador or Brown Barbary Gum-consists of tears of moderate size, often vermiform, and of a rather uniform, light, dusky brown tint. The tears which are internally glassy become cracked on the surface and brittle if kept in a warm room; they are perfectly soluble in water.

Gums of various kinds, including the resin Sandrao, were exported from Morocco in the year 1872 to the extent of 5110 cwt., a quantity much below the average.1

4. Cape Gum-This gum which is uniformly of an amber brown, is produced in plenty in the Cape Colony, as a spontaneous exudation of Acacia horrida Willd. The Blue Book of the Cape Colony published in 1873, states the export of gum in 1872, as 101,241 H.

5. East India Gum-The best qualities consist of tears of various sizes, sometimes as large as an egg, internally transparent and vitreous, of a pale amber or pinkish hue, completely soluble in water. This gum is largely shipped from Bombay, but is almost wholly the produce of Africa; the imports into Bombay from the Red Sea ports, Aden and the African Coast in the year 1872-73, were 14,352 cwt. During the same year the shipments from Bombay to the United Kingdom, amounted to 4,561 cwt.2

6. Australian Gum, Wattle Gum-This occurs in large hard globular tears and lumps, occasionally of a pale yellow, yet more often of an amber or of a reddish-brown hue. It is transparent and entirely soluble in water; the mucilage is strongly adhesive, and said to be less liable to crack when dry than that of some other gums. The solution, especially that of the darker and inferior kinds, contains a little tannin evidently derived from the very astringent bark which is often attached to the gum. A variety of Australian Gum, unknown to us, is described as having" an amorphous white appearance," owing to the infinite multitude of cracks with which the tears are intersected.

Chemical Characters and Composition-At ordinary temperatures gum dissolves very slowly and without affecting the thermometer in an equal weight of water, forming a thick, glutinous, slightly opalescent liquid, having a mawkish taste and decidedly acid reaction.3

1 Consular Reports, August, 1873. 917.

2 Statement of the Trade and Navigation of the Presidency of Bombay for 1872-73, pt. ii. 34. 77.

3 A sample of fine white gum was recently sent to us by a druggist on account of this curious character, that it gave a solution

which was glairy, like the mucilage of marshmallow, but in no other respect could we find that it differed from ordinary gum. On exposing it for some days to a temperature of 95° C., it afforded a solution of the usual character.

At higher temperatures the dissolution of gum is but slightly accelerated, and water does not take up a much larger quantity even at 100° C. The finest gum dried at 100° C., forms with 2 parts of water a mucilage of sp. gr. 1·149 at 15°C.

This solution mixes with glycerin, and the mixture may be evaporated to the consistence of a jelly without any separation taking place. Solid gum in lumps on the contrary, is but little affected by concentrated glycerin. In other liquids, gum is insoluble or only slightly soluble, unless there is a considerable quantity of water present. Thus 100 parts of spirit of wine containing 22 volumes per cent. of alcohol, dissolve 57 parts of gum; spirit containing 40 per cent. of alcohol takes up 10 parts, and spirit of 50 per cent. only 4 parts. Aqueous alcohol of 60 per cent. no longer dissolves gum, but extracts from it a small quantity (to per cent. according to the variety) of resin, colouring matter, glucose, calcium chloride, and other salts.

Neutral acetate of lead does not precipitate gum arabic mucilage; but the basic acetate forms even in a very dilute solution, a precipitate of definite constitution.

Soluble silicates, borates, and ferric salts render gum solution turbid, or thicken it to a jelly. It is not a compound of gum with any of these substances which is formed, but in the case of the first, basic silicates separate. No alteration is produced by silver salts, mercuric chloride or iodine. Ammonium oxalate throws down the lime contained in a solution of gum. Gum dissolves in an ammoniacal solution of cupric oxide. Acted upon by nitric acid, mucic acid is produced.

Small, air-dried lumps of gum lose by desiccation at 100° C., 12 to 16 per cent. of water. If gum independently of its amount of lime, be represented by the formula C12H22O11, 3H2O, the loss of 3 molecules of water will correspond to a decrease in weight of 13.6 per cent.; in carefully selected colourless pieces, we have found it to amount to 13-14 per cent. At a temperature of about 150° C., gum parts with another molecule of water, and loses its solubility.

When gum arabic is dissolved in cold water and the solution is slightly acidulated with hydrochloric acid, alcohol produces in it a precipitate of Arabin or Arabic Acid. It may be also prepared by placing a solution of gum (1 gum + 5 water), acidulated with hydrochloric acid, on a dialyser, when the calcium salt will diffuse out, leaving behind a solution of arabin.

Solution of arabin differs from one of gum, in not being precipitated by alcohol. Having been dried, it loses its solubility, merely swelling in water, but not dissolving even at a boiling heat. If an alkali is added, it forms a solution like ordinary gum. Neubauer who observed these facts (1854-57), showed that gum arabic is essentially an acid calcium salt of arabic acid.

Arabic Acid dried at 100° C., has the composition C12H22O11, and gives up H2O when it unites with bases. It has however a great tendency to form salts containing several equivalents of acid to one of base. An acid calcium arabate of the composition C12H20CaO11, 6C12H22O11, would contain 1.63 per cent. of calcium, corresponding to 3.4 per cent. of calcium. carbonate. Such salts have been prepared by Neubauer and also by Heckmeijer.

The most carefully selected colourless pieces of gum arabic, yield from