pillars, of which 8 are broken, and 16 pilasters, support the roof. Neither the floor nor the roof is in the same plane, and consequently the height varies, being in some parts 17 feet, in others 15 feet. Two rows of pillars run parallel to one another from the northern entrance, and at right angles to it, to the extremity of the cave; and the pilasters, one of which we have described as standing on each side of the two front pillars, are followed by other pilasters and pillars also, forming, on each side of the two rows already described, another row running parallel to them up to the southern extremity of the cave. The pillars on the east and west front, which have been described as like those on the north side, are also continued across the temple from east to west. Thus the ranges of pillars form a number of parallel lines intersecting one another at right angles, the pillars of the central parts being considered as common to the two sets of intersecting lines. The pillars vary both in their size and decorations, though the difference is not sufficient to strike the eye at first. Each column stands upon a square pedestal and is fluted, but instead of being cylindrical is gradually enlarged towards the middle. The capitals exhibit that bulbous form which is one of the most distinctive characteristics of Indian architecture. Above the tops of the columns a kind of ridge has been cut to resemble a beam about 12 inches square, and this is richly carved. Along the sides of the temple are cut between 40 and 50 colossal figures, varying in height from 12 to 15 feet; none of them are entirely detached from the wall. Some of these figures have on their heads a kind of helmet; others wear crowns with rich devices; and others, again, are without any other covering than curled or flowing hair. Some of them have four and others six hands, holding sceptres, shields, symbols of justice, ensigns of religion, weapons of war, and trophies of peace. On the south side, facing the main entrance, is an enormous bust with three faces; of which the central face measures 5 feet in length; the width from the ear to the middle of the nose is 3 feet 4 inches; the breadth of the whole figure is near 20 feet. To the left of this bust, amid a group of uncouth figures, is one (a female figure with four arms) to which Niebuhr has given the name of Amazon, from the fact of its being without the right breast. At the west side of the temple is a recess, 20 feet square, having in the centre an altar, upon which are placed symbols of the worship once practised here. The entrance to this recess is guarded by eight naked figures, each 13 feet high, sculptured in a manner which shows that the people by whom they were executed must have made considerable progress in the statuary's art. The cave is not at present used as a temple, nor has it any establishment of priests connected with it, although it is frequently visited by devotees for the purpose of offering prayers and oblations. The roof of the temple at Elephanta is flat; in others it is hollowed out so as to resemble more or less a regular vaulting. Of this last-mentioned kind is the temple of Kennareh, or Canarah, in Salsette, which is exactly on the same plan as that at Carli, and the principal object or idol is alike in both, consisting, as Moor describes it," of a vast hemisphere of stone resting on a round pedestal of greater diameter having its convexity surrounded by a sort of canopy or umbrella of peculiar construction." The ground-plan of an arched temple of Buddha at Ellora is exactly similar, but there is here a figure of Buddha himself in front of the cylindrical pedestal and characteristic umbrella ornament just mentioned. The temple at Salsette Mr. Fergusson is inclined to reckon among the latest of the Buddhist edifices of this class, regarding it as a copy of the temple at Carli, and as late in date as the 9th or 10th century of the Christian era. The Buddhist rock-cut monasteries are much less rich in detail than the temples. They consist of a central hall, around which are numerous plain cells for the priests of various grades. There were places for private devotion; the public worship and more imposing ceremonies were performed in the temples. The oldest of these caves occur at Behar, in the Bengal presidency, but they are quite unornamented. At Cuttack is one known as the Tiger Cave, from the exterior being carved into the form of a tiger's head, the entrance being through the animal's open mouth. Another in the same neighbourhood is distinguished by being two stories in height, and having a verandah carved along the whole extent of its front. Dr. Impey has published a full account of a series of Buddhistic caves at Koolvee, in Central India, which are "cut literally round the circumference" of a hill, and are in all about fifty in number. Among them are six dagobas (or relicchambers), connected with each of which is a shala, or hall of assembly, and a larger cell for a superior priest. Two only of the caves are "One of supported by pillars, and these are each 32 feet by 24 feet. these caves is subordinate to a dagoba, which stands in a court-yard in front of it, flanked by an erect colossal figure of Budh, in the attitude of expounding; and the other to a seated image of Budh, which is in a cell opposite the porch flanked on either side by diminutive dagobas in relief." The figures are of rude execution, and much defaced and weatherworn. The inferior cells are all small in size and quite simple in plan. The walls of the larger chainbers of some of these rock-monasteries are profusely decorated with paintings of religious and historical subjects, executed in fresco or distemper, portraits of Buddha and Buddhist saints covering the pillars, and the roofs being at the same time painted with scrolls and other architectural designs. In many places these paintings have been destroyed by the effects of damp, or by the hand of man, but at the Ajunta and elsewhere they "remain nearly complete, and as fresh as the day they were painted. A competent artist, Capt. Gill, of the Company's Service, has been employed for some years in copying these." Their publication would doubtless, as Mr. Fergusson remarks, throw light not only on the " manners and customs of India more than a thousand years ago, but illustrate also to a considerable extent the form and ordinance of the buildings they adorn." Dr. Impey (Journal of the Royal Asiatic Society,' Bombay Branch, July, 1856,) describes a series of historical and mythological paintings on the famous caves of Bágh in Rath, on the Nerbudda, which still extend above 220 feet in length. The paintings are in a double row, one set above the other, the figures being about the natural height. The designs are very varied, and display no little skill. "The surface extent of the work thus elaborately depicted must have been at least 3000 feet." They appear to be not later in date than the 5th century, A.D. The other Buddhist religious edifices have been all classed under the general term Topes. They consist of detached pillars and towers, and of buildings, usually circular in form but always surmounted with a dome. The pillars are the oldest. All that remain in India proper are monoliths, but there appears to be little doubt that built pillars did formerly exist; and Mr. Fergusson, who adduces two such pillars as still standing among the topes of Cabul, thinks that their destruction is "sufficiently accounted for by the ease with which they could be thrown down and their materials removed, when they had lost the sanctity by which alone they had been protected." Of these monoliths, or lâts, the oldest known were erected by Asoka about 250 B.C., and bore inscribed on them the Buddhist creed. Three of them are still standing near the river in Tirhut, and are each surmounted by a seated lion. One which has been removed and set up on a pedestal at Allahabad, is 47 feet high, and the shaft is 3 feet in diameter at the base, diminishing to 2 feet 2 inches at the summit. It is noteworthy that "the necking immediately below the capital represents, with considerable purity, the honeysuckle ornament of the Assyrians." (Fergusson). They were most probably always erected in front of temples and sanctuaries, where some are still found. The topes properly so called are spacious circular domical buildings, erected as reliquaries of Buddha or some of the more eminent Buddhist saints. They occur in groups near the Indus and the Ganges, at Behar and Tirhut, around Bhilsa in Central India, and in Affghanistan. These topes will be found fully described in the valuable works of Mr. Fergusson, and in the elaborate treatise of Major Alexander Cunningham, The Bhilsa Topes; or Buddhist Monuments of India,' 8vo. 1854. The oldest of these topes are little more than tumuli; later the hemispherical cupola was supported on a cylindrical basement; and eventually they assumed the character of a tower surmounted with a cupola. In size they vary from a few feet up to 150 or 200 feet in diameter. The great Sanchi Tope, near Bhilsa, the finest and most perfect in India, will serve as an example of this class of buildings. It is situated on the western side of a lofty hill, and is inclosed within a great court-yard which averages 150 yards in length, and is 100 yards broad. "The great tope itself is a solid dome of stone and brick, 106 feet in diameter and 42 feet in height, springing from a plinth of 14 feet, with a projection of 5 feet from the base of the building, and a slope of 2 feet. The plinth or basement formed a terrace for the perambulation of worshippers of the enshrined relic; for on the right pillar of the North Gateway there is a representation of a tope, and of two worshippers walking round it with garlands in their hands. The terrace was reached by a double flight of steps to the south, connected by a landing ten feet square. The apex of the dome was flattened into a terrace 34 feet in diameter, surrounded by a stone railing of that style so peculiar to Buddha monuments, that I will venture to call it the Buddhist Railing." This terrace formed the basis of the tee or capital (a square box-like ornament probably intended to serve as a relique-case or a symbol of one) with which these structures were always crowned. "The total height of the building, including the cupolas," continues Major Cunningham, “must have been upwards of 100 feet. The base of the tope is surrounded by a massive colonnade, 144 feet in diameter from east to west, and 151 from north to south." The entrance is by four gateways, each formed by two square pillars, 18 feet high, covered with carvings, and crowned with elephant capitals. These support three elaborately carved lintels slightly curved upwards in the centre, and terminating in Ionic scrolls and surmounted with emblems: in all the gateways are 33 feet high. On all sides are ruined temples, fallen columns, and broken sculptures; while 30 or 40 smaller topes combine to form the group of which the great tope is the centre. With respect to the character and arrangement of the topes, it will be enough to quote what Major Cunningham says of those of Bhojpur: "The topes occupy four distinct stages or platforms of the hill. The largest topes, six in number, occupy the uppermost stage, and were, I believe, dedicated to Buddha; that is, either to the celestial Buddha, Adináth, or to the relics of the mortal Buddha, Sákya. This view is borne out by the facts that the largest tope contained no deposit; and that the second and third sized Topes yielded crystal boxes, one of which, shaped like a tope, contained only a minute portion of human bone smaller than a pea! The second rate topes, sixteen in number, stand on the second stage. According to my view, these topes contain the ashes of those who had reached the rank of Bodhisatwa. We discovered relics in five of these topes, but there were no inscriptions of any historical value. The third stage of the hill is occupied by seven small topes, all of which I suppose to have been built over the remains of the third grade of Pratyeka Buddhas. Of the eight topes which stand on the lowest stage of the hill, one is m ich larger than any of those on the third stage. These topes were, I believe, built over the ashes of the lowest grade of the Buddha community, the Sráwaka Buddhas." Very splendid examples of Buddhist temples, topes, an ddagobas occur, at Anuradhapoora, the ancient capital, and in several other places in the island of Ceylon. These, from their having escaped the destructive hand of adverse religious bodies, serve to elucidate n any interesting points in the history of Buddhist architecture which the remaining monuments of the peninsula leave in obscurity. Our space will not, however, allow us to notice them here: they will be found described in the works of Mr. Fergusson and Sir Emerson Tennent. In Burmah also occur numerous costly Buddhist edifices, some of them on a scale of great magnitude, as the great pagoda of Pegu-a comparatively modern structure-the diameter of whose base is 395 feet, while its height is 331 feet above the artificial terrace on which it stands. At Java again are several vast Buddhist temples, as that of Boro Buddor, which is a square nine-storied many-pinnacled pyramid, the base of which is 400 feet across. In style, however, these last are far more barbaric than the older buildings of Hindustan. Based on the Buddhist style, but much more highly ornamented, are the temples erected by the Jainas, the great sect which sprang up at the decline of the Buddhists. [JAINAS.] Some of these temples are distinguished alike by chasteness, symmetry, and beauty of design, and by rich and exquisite finishing. That at Ajmeer, in Rajpootana, is remarkable for the elegance and slenderness of its columns, so very different in their character from those in the excavated works, and which seem therefore to indicate a totally different period of art. They are about forty in number, and partake somewhat of a candelabrum shape, although no two are exactly alike. The ceiling is highly enriched with square panels or coffers, containing others in the form of lozenges, enriched with foliage and sculpture, in style not very much unlike the cinquecento of the Italians. This temple is surrounded by a superb screen of Saracenic architecture, assigned by Tod to the first dynasty of the Ghorian Sultans. The same writer dwells upon the analogy observable between the details of the columns in this temple and the ornaments of Gothic buildings; and it would hardly be fanciful to designate Jaina architecture the Decorated Buddhist style. Some of the oldest and finest examples of the style are found about Mount Abu in Gujerat, but they occur over a wide space, though often altered, like the temple at Ajmeer, by Mohammedan additions. The temples appear always to include a sanctuary, lighted only from the door, and terminated upwards by a pyramidal spire-like roof. In this chamber is placed a seated figure of the saint to whom the temple is dedicated; and attached to it is a spacious portico, which is sometimes surmounted by a cupola. These porches are often extremely rich in ornamentation: that of the temple of Vimalah Sah at Abu (described and figured by Mr. Fergusson) has 48 elaborately carved columns; yet the exterior of the temple is perfectly plain. The Jainas were the first to erect hollow cupolas in India, those in the Buddhist topes being all solid. The cupolas of the Jaina temples are formed by placing the stones so as gradually to project one beyond the other, the apex being closed by a circular key-stone. The principle therefore is that of a horizontal or vertical instead of a radiating pressure, and the edges of all these projections being rounded off, the spectator sees, on looking up, a vault composed of gradually diminishing circles or annular courses of masonry. Brackets and struts are occasionally employed with great skill to assist in bearing the superstructures. According to Mr. Fergusson, some of these Jaina cupolas are "the most exquisite specimens of elaborate roofing that can anywhere be seen." Usually the octagonal cupolas are carried on eight thick pillars; but the base is always made square by the addition of four other pillars at the angles; while in smaller buildings two more are added on each face, making twenty in all. Sometimes, however, the same system of aggregation is carried on till the number reaches fifty-six, which is the largest number I ever saw surrounding one dome; but any number of these domes may surround one temple, or central dome, and the number of pillars consequently be multiplied ad infinitum." (Fergusson.) The variety, picturesqueness, and splendour of effect, and the rich play of light and shade, thus produced, however impure the style of architecture may be in itself, can readily be imagined. Many of the most superb of the Jaina temples have been converted into Mohammedan mosques. The Jainas appear to have also wrought out cave-temples; among others the Subba caves of Ellora have been attributed to them; but there is nothing in their works of this class sufficiently distinctive to call for a particular description. Following their Buddhist predecessors, the Jainas showed a great partiality for erecting towers; and their towers, though less substantial, were little less rich than their temples. Few of them however are left now. Two of them still stand within the fort of Chittore. The older and smaller is of the 10th century, A.D.; the larger is of the 15th. This last is 30 feet wide at the base; 120 feet high; and is formed in nine stories, the whole being covered with architectural and sculptural ornament. The body, or shaft, of the tower is smaller than the base, but it swells out again towards the summit, which is surmounted with a small dome, and which was probably crowned with a tee. It is fully described and figured in Mr. Fergusson's 'Illustrations of Indian Architecture,' and ' Handbook of Architecture.' This class of dagoba is the immediate prototype of the Chinese ninestoried pagoda. Brahman Architecture is best studied in the temples of Southern India. In Northern India the style is a good deal varied and less pure, What may be considered as the normal type of a Brahman temple consists of the vimana, a tower square in plan and pyramidal in form, built over the sanctuary or cell in which is the image or emblem of the god; a mantapa, or porch, placed before the principal entrance to the sanctuary; gopuras, or pyramidal gate towers, which serve as entrances to the enclosures in which the vimanas are placed; and a choultrie, or spacious pillared hall. The Vimana, or inner temple, has a perpendicular base of granite or stone, which is always decorated with pilasters, niches, and other architectural ornaments. From this rises in distinct stages the pyramidal roof, usually constructed of brick and covered with stucco, and crowned with a small dome-like termination, evidently borrowed from the older Buddhist builders. The most splendid example of one of these buildings is the great temple at Tanjore, from the annexed representation of which their general character may be understood. The base of this temple is 82 feet each way, and the pyramidal roof rises in 14 stories to a height of about 200 feet. The porch, or Mantapa, is in plan usually similar to the temple itself, a crowning ornament. Placed against the door of the cella, the mantapa effectually excludes the light of day from the sacred chamber, which consequently is lighted only by lamps. The Gopuras, or gate-pyramids, which give entrance to the rectangular court which encloses the temple, are usually proportioned in size and number to the length of wall which surrounds the court. Some of these gateways are much larger than the temples to which they are appended, and the entire surface of many of them is covered with ornament. One at Combaconum is 12 stories high. In form they are similar to the vimanas, except that they are not so deep as they are wide, and they are always pierced with a doorway occupying from a fourth to a seventh of the whole width. "By far the most extraordinary buildings connected with these fanes are the pillared colonnades or Choultries, which occupy the spaces between the various enclosures of the temples. They are of all shapes and sizes, from the little pavilion supported on four pillars up to the magnificent hall numbering a thousand. Their uses too are most various; in ancient times they served as porches to temples; sometimes as halls of ceremony, where the dancing girls attached to the seminary dance and sing; sometimes they are cloisters, surrounding the whole area of the temple; at others swinging porches, where the gods enjoy at stated seasons that intellectual amusement. But by far their most important application is when used as nuptial halls, in which the mystic union of the male and female divinities is celebrated once a year. Those dedicated to these festivals sometimes attain an extent of 1000 colunins, and are called in consequence halls of 1000 columns, though they do not in all instances make up this complement." (Fergusson.) The pillars are in most instances composed of granite, and covered with sculpture from the base to the capital, every pillar being usually unlike the others in the details, though similar in general character and dimensions. The effect of many of these halls is very impressive. As an example of the style of southern Hindustan we may refer to the small but very elegant temple at Bareilly, as a structure of most complicate and exquisite workmanship. Although placed within an area about 250 yards square, the body of the temple, or sanctuary (mindra), over which rises a pyramidal sikr, or roof, is only 21 feet square, but the addition of the domed vestibule (munduf) and the projecting portico composed of four superb columns makes the whole 44 feet by 21. The ceilings are elaborately worked, and that of the portico consists of a single block. Facing this temple is another splendid edifice, called the Séngár-chaori, or Nuptial Hall, a square of about 40 feet, with a double range of pillars on each side forming open colonnades. Its sikr is the frustum of a pyramid, each stone of which is elegantly carved, and gradually decreasing in size to the kullus or ball. After the introduction of the Saracenic architecture by the Mohammedan invaders, the Hindu architects adopted in their secular buildings many of the features of the new style. Some of the palaces constructed under this foreign influence are extremely picturesque, as the palace of Madura, commenced in the early part of the 17th century. But the decline of Hindu architecture was thenceforth rapid; innovations of all kinds were introduced, and the native barbaric magnificence, originality, and piquancy were lost, without being replaced by western purity, simplicity, or taste. 66 The Mohammedans at first, it is evident, were led to imitate much both of the general forms and the details of the ecclesiastical architecture of the people they had conquered. But they brought with them the principle of the arch, and with it a different and more daring style of construction. They never wholly abandoned the forms they had adopted from the Hindus; but they so modified and applied them that ultimately their style became rather a variety of the true Saracenic or Moorish style than of either of the styles of India. Hodges, who has carefully studied the original buildings, indeed refers us to the mosque at Chunar Gur, on the Ganges, as a proof of the "perfect similarity of the architecture of India brought thither from Persia by the descendants of Timur, and that brought into Europe by the Moors of Spain." "All the minuter ornaments," he says, are the same, the lozenge square filled with roses, the ornaments in the spandrels of the arches, the little panellings and their mouldings; so that a person would almost be led to think that artists had arrived from the same school, at the same time, to erect similar buildings in India and in Europe." This is, however, too strongly put, and is contradicted by the details of his own plates. There are, in truth, many features in the Mohammedan architecture of India which stamp it as distinct from the Moorish style of Europe. [SARACENIC ARCHITECTURE.] Among these are its numerous bulbous domes, which are frequently applied even to minarets, and the projecting galleries given to these latter, to which may be added the use of very projecting balconies, supported on massive cantilevers or consoles. One of the most splendid examples of this later style is the celebrated Taje Mahal, near Agra, erected by Shah Jehan as a mausoleum for his wife in the 17th century. "It stands," says Bishop Heber," in a square area of about 40 English acres, enclosed by an embattled wall with octagonal towers at the angles, surmounted by open pavilions, and four very noble gateways of red granite, the principal one of which is inlaid with white marble, and has four high marble minarets. The space within is planted with trees and divided into green alleys leading to the principal building, which is a sort of solid pyramid surrounded entirely with cloisters, galleries, and domes, diminishing gradually till it ends in a square platform of white marble, surrounded by a most elaborate lattice-work of the same material, in the centre of which is a small altar-tomb, also of white marble, carved with astonishing delicacy and beauty." The cost of this tomb is said to have been 750,000l. An equally celebrated but inferior work of this class is the mausoleum of Hyder Ali at Seringapatam. Next to the tombs, perhaps, as characteristic of Mohammedan architecture in India, are the mosques, some of which are of considerable magnitude and magnificence. In the gateways, which are made a striking feature, the Moorish arch inclosed within a square-headed panel is applied with excellent effect. In the mosques themselves there is often a great multiplicity of hemispherical or bulbous domes. The mosque at Mandu, the great mosque at Delhi, and the pearl mosque of Shah Jehan at Agra, are very beautiful examples of Mohammedan temples. Some of the minarets are highly enriched and of unusual dimensions; that of Kootub is 48 feet at the base and 242 feet high, though it has lost its capital-being only exceeded among Mohammedan buildings by the minaret of the mosque of Hassan in Cairo. Still more splendid are, or were, the palaces, which are in some instances of prodigious extent, finished in a style of unbounded luxu riance, full of fanciful and admirably-executed ornamental details, and unquestionably picturesque in appearance. Among the most superb are those of Agra, Allahabad, Lucknow, and Delhi. INDIAN FIRE. A brilliant white signal-light, produced by burning a mixture of 7 parts of sulphur, 2 of realgar [ARSENIC], and 24 of nitre. INDIAN INK. [INK.] INDIAN RUBBER. [CAOUTCHOUC.] INDICATOR. The word indicator is used, generically, in mechanical engineering, to designate any contrivance by means of which it is possible to calculate the force exerted by the intervention of a machine; but it has of late years been almost exclusively applied to the instru ments by which the pressure of steam in the cylinder of a steam-engine is registered throughout the whole of its duty, or by which the amount of vacuum or exhaustion attained by the use of the air-pump and con denser, is recorded. The indications of the pressure of steam in the boiler are marked by the pressure gauge; the indications of the useful amount of power transmitted to the first motion-wheel are recorded by the dynamometer; whilst the meaning of the generic term is limited to the sense above given. Different constructors have introduced varieties in the form and working details of their indicators; but they all are identical in principle. They are all self-registering, and show (by means of a curve traced on a slip of paper by a pencil attached to the part of the indicator immediately connected with the steam in the interior of the cylinder, or with the vacuum), the difference between the pressure of the atmosphere around the cylinder, and the pressure within the cylinder, at every part of the up and down stroke of the piston, for that end of the cylinder to which the indicator is attached. In order to effect this object, a small cylinder is connected with the larger one in which a steam and air tight piston works, and the rod of this piston passes into another small cylinder, in the interior of which is placed a spiral spring, which in its turn presses upon the rod of the indicator piston in such a manner as to keep the latter in the centre of its cylinder, when the pressure of the atmosphere and of the vapour in the cylinder of the engine balance one another. In proportion as the relative pressure increases on either side of the cylinder of the indicator, it will be found that the piston will rise or fall; for spiral | springs (as Messrs. Hann and Gener observe), are extended and compressed through equal spaces by equal and opposite pressures. There is a stud passing from the top of the piston-rod through a slot in the spring cylinder, and an index pointer shows on a scale attached to the side of the slot the pressure acting upon the piston. The description and use of this instrument are well explained in Hann and Gener's book, above quoted, entitled 'The Steam Engine,' 1854, &c. &c. INDICTION; CYCLE OF INDICTION. [PERIODS OF REVOLUTION.] INDICTMENT is a written accusation of one or more persons of a crime or misdemeanour presented by a grand jury. The sheriff returns to every session of the peace and every commission of oyer and terminer and jail delivery at least twenty-four freeholders of the county, twelve of whom, at least, and not more than twenty-three, are sworn upon the grand jury. They are instructed in the articles of their inquiry by the judge, and then withdraw to sit and receive bills of accusation, which are presented to them in the name of the crown, but at the suit of any private person. The decision of the grand jury is not in the nature of a verdict as to the guilt of the accused, but merely the expression of their opinion that from the case made by the prosecutor the matter is fit to be presented to the common jury. In conducting the inquiry the evidence in support of the accusation only is heard. If the grand jury think the accusation groundless, they indorse on the bill "not a true bill," or "not found;" if the contrary, "a true bill;" and in finding a true bill twelve at least of the grand jury must concur, because no subject can be put to answer an accusation except such as is credited by such a number of his fellow citizens. Anciently the words "ignoramus" and "billa vera' were used. When a bill is found to be a true bill, the trial of the accused takes place in the usual form; when the bill is "ignored," the accused is discharged, but a new bill may be preferred against him before the same or another grand jury. Sometimes, when the bill is ignored on account of some slip or error, the judge will direct the accused to be kept in custody, in order to prevent him from escaping from justice. INDIGESTION. [DYSPEPSIA.] INDIGO. This well known colouring matter is a product of the vegetable kingdom, being derived from the cellular tissue of the leaves of certain plants. For the names and habitats of these plants, see INDIGOFERA, in NAT. HIST. DIV. Indigo was well known to the ancients. Bands of cloth, evidently dyed with this material, are met with in the wrappings of Egyptian mummies; and Dioscorides and Pliny mention it as an Indian product under the names of dikov and indicum. It began to be employed in Europe about the middle of the 16th century, but owing to the opposition of the cultivators of the native woad, its importation into England was prohibited; and it was not till the time of Charles II. that these prejudices were overcome. At the present time there are sent into this country from 60,000 to 70,000 cwts. of indigo per annum. The cultivation of the indigo plants is extensively carried on, in various parts of India and America. In the spring the seeds are sown, at the rate of about a dozen pounds per acre; the plants grow rapidly, commencing to blossom in three months time, when they are cropped and again allowed to grow till they are sufficiently mature to admit of another cutting. Occasionally a third and even a fourth cropping is made, but each of these contains successively less and less of the matter that yields the colouring principle. The indigo plants present no appearance when growing that would lead an observer to suppose they contained any matter capable of producing colour; nor is it yet satisfactorily determined in what form the indigo pre-exists in the vegetable tissues. From the recent experiments of Schunk (Manchester Memoirs,' 1855, vol. xii., p. 177), it would seem that a principle, termed by him Indican, of yellow colour, and having the composition (C,,H,,ÑO?), occurs naturally in the plants, and that it is from the decomposition of this body, under circumstances immediately to be described, that the indigo is produced. The manufacture of indigo in the East Indies is conducted some ARTS AND SCI. DIV. VOL. IV. what after the following plan. The recently cut plants are placed in large stone cisterns, called fermenting vats, or steepers, and covered with water; fermentation soon commences, large quantities of gas rise in bubbles to the surface, and the whole mass becomes covered with a copper-coloured scum. After about fifteen hours fermentation ceases, and the liquor is then run off into another vat placed on a lower level. Here it is brought well into contact with the air by beating with wooden paddles for about an hour and a half. During the beating the contents of the vessel darken in colour, and the indigo separates out in flocks; these are allowed to subside, heated to boiling to effect the removal of certain impurities, then collected on woollen strainers, and finally pressed, dried, and the mass cut up into blocks for sale. At some places the plants are, after cutting, spread out to dry in the sun, it being supposed that a better quality of indigo is thus obtained. Indigo is usually met with in commerce under the form of cubical masses or cakes, which are brittle and of characteristic colour, a colour that ranges from a deep blue containing a little purple, to a dark purple containing a little blue. When burnished it acquires a beautiful, glossy, copper tint. It is generally thought that its specific gravity should be less than that of water, though the method of preparation and adulteration with foreign matters often cause it to weigh more than an equal bulk of that liquid. Many methods for estimating the absolute amount of colouring matter-indigotin-in a specimen of indigo have been proposed, but they all require experience in chemical manipulation for their accurate performance: they will be found described in the various analytical text-books. The great value of indigo as a dyeing material, and the enormous extent to which it is used, have procured for it a large share of the attention of scientific chemists. The result is that its application as a pigment has been greatly extended, and many important and interesting derivatives obtained from it. The following list will exhibit at a glance the relations which the chief of these derivatives bear to each other. Starting with pure indigo itself (indigotin), which may be looked upon as a positive radical, and which we may represent by the symbol (In=indyl), we have :— Indigo-blue or indigotin (CH.NO,), may be obtained in a very beautiful form by mixing commercial indigo with about half its weight of plaster of paris and sufficient water to make a thick cream; this is evenly spread over an iron plate so as to form a stratum about oneeighth of an inch in depth, and set aside to dry. A spirit or gas flame is then applied to the under surface of the plate when the indigo sublimes out from the mixture and condenses in brilliant little purplishbrown crystals, on that part of the plaster immediately over the source of heat. By gradually moving the lamp the indigo is sublimed in successive portions that readily admit of being removed by a spatula from the hard cement below. Indigo-blue thus produced is very beautiful, but not pure. To obtain it in the latter state, it is necessary to dissolve it in a dilute alkaline solution, and as indigo itself is not soluble in such a menstruum, it is brought into intimate contact with some substance that is capable of furnishing hydrogen to it, hydride of blue indigo being thus formed which is quite soluble. One of the best methods of accomplishing this is the following. Four parts of indigo in powder, four parts of grape sugar, and ten parts of a saturated solution of caustic soda, are placed in a flask of such a size that it will hold about twenty times the volume of the mixture. The vessel is now filled up with boiling alcohol, well stoppered, briskly agitated, and set aside. The liquid soon becomes clear, and is then poured out into shallow vessels and exposed to the air, when it rapidly absorbs oxygen and deposits crystals; these when washed, first with alcohol and then with hot water, form perfectly pure indigo blue. Indigo-blue is a neutral body, tasteless and inodorous. It is insoluble in water, alcohol, ether, oils, dilute acids, or alkalies. It fuses and sublimes in purple-coloured vapours at about 550° Fahr.; at a higher temperature it is decomposed, hydrocyanate and carbonate of ammonia, aniline, and an empyreumatic oil being among the the volatile products, while much carbonaceous residue remains. White Indigo, Indigogen, or (improperly) Reduced Indigo (CH.NO, =CHNO,,H) is a combination of hydrogen with indigo blue, and may be prepared by several processes: all of which, however, depend upon the deoxidising effect they have upon water, the hydrogen of that compound being thus furnished to the indigo. Grape sugar is such a deoxidising or hydrogenising agent, and if to the dilute alkaline solution (already referred to in the description of the method for obtaining pure indigo blue) there be added acetic acid, dirty white flocks of indigogen are precipitated. White indigo is insoluble in water, slightly soluble in alcohol and in ether, and when exposed to the air rapidly absorbs oxygen, forming water and indigo-blue. 3 1 The solubility of white indigo in a dilute alkaline solution, and the insolubility of blue indigo in a similar menstruum, are facts of great interest and importance, as on them depend the use of indigo in the arts of dyeing and calico-printing. The deoxidising agents, other than grape sugar, that are used for making the reduced indigo vats, are protosulphate of iron, protochloride of tin, orpiment, and decaying vegetable matter; lime sometimes replacing the alkali. For details of the preparation of some of these baths or vats, see CALICO-PRINTING and DYEING. Η Sulphindigotic acid, or Sulphindylic acid (In,S,O=C, NO,,SO). One equivalent of hydrogen in this compound is replaceable by an equivalent of metal, forming salts called sulphindigotates or sulphindylates. Sulphindigotic acid is formed by dissolving commercial indigo in six times its weight of fuming or Nordhausen sulphuric acid. The product is known as Saxony blue, and is extensively used in cloth dyeing; it contains another acid named hyposulphindigotic acid, and the greater part of the residue from its preparation consists of sulphopurpuric or sulphophenicic acid (2C, H,NO,,S,O). By the decomposition of these sulphuric derivatives of indigo there are produced sulphoviridic, sulphoflavic, sulphofulvic, and sulphorufic acids: they have been but little studied. Isatin (C,H,NO,), a substance obtained from indigo by the addition of two equivalents of oxygen. In order to prepare it, powdered indigo is to be mixed in water with equal parts of sulphuric acid and bichromate of potash, the last being dissolved in 20 or 30 parts of water. The indigo dissolves, and at first without the extrication of any gaseous matter, but towards the end with the disengagement of carbonic acid gas, and the formation of a deep yellowish brown liquid, from which the isatin separates by evaporation, in crystals; these are purified by repeated crystallisations in water, and one and the last in alcohol. Nitric acid may be used in the place of chromic for oxidising the indigo, but if too concentrated, indigotic acid (nitrosalicylic acid) results. The properties of isatin are:-It crystallises in prisms, which are of a yellowish red or deep aurora-red colour, possessing much splendour when deposited from an alcoholic solution; they are slightly soluble in cold water, but dissolve readily in boiling water and in alcohol; these solutions discolour the skin, and impart a disagreeable odour to it. The crystals are decomposed by heat, leaving a charcoal which it is difficult to incinerate; the caustic alkalis convert it into isatic acid. Fused with solid hydrate of potash it is decomposed, aniline being produced according to the following equation : which dissolves when heated in the mixture, a certain portion of the silver salt being reduced to the metallic state; the boiling solution of isatate of silver deposits crystals which are partly in lamina and partly granular. The general formula of these isatates is (CH,MÑO.= MO,C,H,NO。). These compounds greatly resemble isatin, both in appearance and in all their reactions. The chlorine derivatives are produced by the action of chlorine upon indigo, and separated by crystallisation from alcohol, chlorisatin being less soluble in that liquid than dichlorisatin. The bromine derivatives are obtained in a similar manner from indigo, using bromine instead of chlorine. 10 They are respectively produced by the action of potash upon chlorisatin, dichlorisatin, bromisatin, and dibromisatin, the potash salt of the acids being thus formed, and this, by double decomposition with the soluble salts of other bases, furnishes the several metallic derivatives of these acids. Ammoniacal Derivatives of Isatin.-Ammonia acts upon isatin, giving rise to bodies that differ from each, according as the circumstances differ under which they are brought into contact. They all contain the ele ments of isatin, plus ammonia (NH,) and minus water (HO). Their relations to each other are best shown by formulating them upon the ammonia type, or upon the hydrated oxide of ammonium type, as follows, in which blue indigo-that is, the radical indyl (CH ̧ÑÒ ̧)— is represented by the signs (InIn or In.). Isatic acid (CH,NOHO,C,H,NO,). Isatin dissolves in potash with a deep purple colour, which becomes bright yellow by heat. The solution yields by evaporation a crystalline salt of potash, which is soluble in alcohol, and crystallises in small, hard, colourless prisms. When a solution of this salt is mixed with one of acetate of lead, a white precipitate is obtained, which, diffused in water and decomposed by hydrosulphuric acid, yields a colourless acid liquid, and this by spontaneous evaporation furnishes a white and scarcely crystalline powder, which is hydrated isatic acid. The properties of isatic acid are as follow:-It is perfectly insoluble in cold water; but when heated in water, it is decomposed into isatin and water, the mixture becoming of a reddish yellow colour: the soluble isatates act in the same manner with the mineral acids; when they are added to it cold, no decomposition is apparent; but as soon as heat is applied, the mixture becomes yellow, and deposits crystals of isatin. Isatate of potash gives a white precipitate with barytic salts, soluble in boiling water; with the salts of silver it gives a white precipitate, Each of the chlorine and bromine derivatives of isatin gives rise to a similar class of bodies, in each of which, of course, isatin is replaced by the chlor or brom derivative. Imesatin is obtained in colourless prisms on passing a current of dry ammoniacal gas through a solution of isatin in absolute alcohol. Imasatin is produced when a solution of isatin in ammonia is maintained for a short time at the boiling point. It crystallises in lamellar grains. Isamic, called also imasatic and rubendinic acid, crystallises out in beautiful plates from an alcoholic solution of isamate of ammonia, to which hydrochloric acid has been added. Isamate of ammonia results from the metamorphosis of isatate of ammonia when a solution of the latter salt is evaporated to the consistence of a syrup. Bromine energetically attacks isamic acid, producing a yellow body termed nia is strongly dried. Isatimide is a crystalline yellow powder formed indelibrome. Isamide, or amasatin, is formed when isamate of ammoduring the preparation of imesatin, but is more soluble in the alcoholic ammonia, and therefore crystallises out subsequently to the imesatin. There appear, also, to be produced at the same time, isatilime (CHNO10), containing three atoms of isatin, plus one of ammonia, minus two of water; and amisatin (CH ̧NO), represented by six atoms of isatin, plus five of ammonia, minus six of water. 16 Isathyd (CH NO,=С1H ̧ÑO,, H).-This body may be viewed as the hydride of isatin, bearing the same relation to that body that white indigo does to blue. It is best prepared by placing isatin in a flask with zinc and dilute sulphuric acid. It is a grayish crystalline powder, insoluble in water and sparingly so in alcohol or ether. On passing a current of sulphuretted hydrogen through the alcoholic solution, bisulphysathyd (CH,NO,S,) is formed, a body in which two atoms of sulphur replace two of the oxygen in isathyd. On adding solution of potash drop by drop to an alcoholic solution of bisulphisathyd, one atom of sulphur is substituted by one of oxygen, and sulphisathyd is produced. By the action of hydridising agents upon the chlorine and bromine derivatives, corresponding chlor and brom isathyds are obtained. Isatane (CH.NO) is a white powder, formed when bisulphisathyd is boiled with bisulphite of ammonia. It contains the elements of two molecules of isathyd, less two atoms of oxygen. Indin is prepared by the action of potash on sulphisathyd, the alkali being subsequently removed by hydrochloric acid. It is pulverulent, of a very fine deep rose-red colour, insoluble in water, and slightly soluble in alcohol and ether. When heated, it begins to swell as soon as it melts. It yields a substance which crystallises in needles, and much charcoal remains. Boiling nitric acid decomposes it, altering its colour slightly, red vapours are formed, and nitrindin (C2H.(NO)N ̧O) is produced. If the ebullition be continued, the new product is also decomposed, and disappears. Sulphuric acid dissolves indin, assuming a red colour, and water precipitates it from solution unaltered; bromine colours it violet. Ammonia has no action on indin, but potash attacks it under certain circumstances. It is polymeric with blue indigo, and its probable composition is (C22H10N2O.). 32 101 |