safety plugs of fusible metal formed of lead, tin, and | at Borrowdale has long maintained the pre-eminence, bismuth have been used in steam boilers to provide against explosion. It was supposed that if the temperature of the steam should rise above a certain point, and the safety valve not be in a condition to allow of its escape, the plug would fuse, and afford a vent. It has been found, however, that when this alloy is exposed during a long period to a temperature near its fusing point, it undergoes a sort of eliquation, [See AsSAYING,] by which a more fusible alloy is melted out, and that which remains is much less fusible than the original alloy. In some explosions of boilers, the safety plugs have for this reason been found entire. Hence this mode of protecting boilers has been abandoned. Fusible metal has been successfully employed for making casts of anatomical preparations, and other similar purposes. Professor Brande says:- -"It may be employed for taking casts from medals, and even from the surface of wood and embossed paper. Some beautiful casts have also been made in this metal of the internal ear, showing the complexities of its bony cavities." Cake moulds for the manufacturers of toilet soaps are also made of this metal. BITTERN. The mother-liquor or uncrystallizable residuary solution of SALT WORKS, so called on account of its excessively bitter taste. Its principal ingredients are chloride of magnesium and sulphate of magnesia or EPSOM SALTS. BITUMEN. [See ASPHALTUM.] BLACK-LEAD. PLUMBAGO. GRAPHITE. A mineral substance occurring in veins, and in kidney-shaped lumps, in gneiss, mica slate, and their subordinate rocks; also in transition slate, as in the valuable mine at Borrowdale, in the heart of the lake district of Cumberland. Black-lead has probably received its name from its colour, which is of a leaden or slaty grey, passing into iron black, but there is not a particle of lead in its composition. According to Vanuxen, the pure and impure varieties from Borrowdale contain : The ashes of plumbago are found to contain titanic acid, and "it seems probable," says Brande, "that in plumbago the oxide of iron is in combination with titanic acid and silica, and not with the carbon, so as to constitute a carburet of iron." Some specimens, as those from Barreros in Brazil, scarely contain a trace of iron. Black-lead has been found among the coal-strata, as at Cumnock in Ayrshire; it has also been found in greater or less purity, and occasionally worked in many other parts of the world, especially in the United States of America; but the English mine so that the " crayons d'Angleterre" are in great esteem throughout the continent. The Borrowdale mine was discovered in the reign of Elizabeth, and soon became celebrated for its valuable contents. The work-people engaged in it, and those from neighbouring mines, were not proof against the temptations to plunder. The latter would even cut their way through from their own mines, and carry off quantities of the black-lead. On one occasion a party of miners overcame the guard placed at the entrance, and kept possession of the whole place for several days. These depredations were resisted with difficulty, and were not put a stop to until many persons in the vicinity of the mines had become enriched thereby. At length an act of parliament was obtained, inflicting severe penalties on depredators, and this, with improved means of defence, has proved an efficient protection. The mine is situated about half way up the side of a mountain called Seatallor Fell, in Cumberland, eight miles south of Keswick, and which rises to the height of 2,000 feet. From the entrance to the mine a horizontal cavity is excavated to the extent of several hundred feet into the body of the mountain, having a railway laid down for the transit of the ore. The entrance is protected by a substantial building, in which is a room for assorting and dressing the ore, which process is performed under strict surveillance, and with the threatening aspect of firearms. These is also a room called the dressing-room, in which the workpeople change their garments previous to entering the mine, and again after six hours' work, on leaving. In this room is a trap-door which forms the miners' only means of entrance to the mountain. The plumbago is of a fine granular texture, and so pure that it requires very little labour to fit it for the market. When it has been assorted and dressed, it is packed in strong casks holding about a hundredweight each, and is thus forwarded to the proprietors in London. In former times this mine was only opened once in seven years, but owing to the increased demand for plumbago, it is now opened every summer for about six weeks, and during that short period as much as 30,000l. or 40,000 worth of mineral is sometimes obtained. The closing of the mine is accompanied with laborious precautions for insuring its safety. The earth and rubbish previously excavated are wheeled back again to the opening of the mine, and heaped up there to the amount of some hundred cart-loads. This forms a dam to a rill of water which flows through the mine, and which being thus deprived of the means of outlet, rises to a considerable height, floods the mine, and affords the best protection against robbery. This important mine is shared between a few individuals, and the product fetches from 35s. to 45s. per lb. in the market. The market for black-lead is held monthly in London, at Essex Street, Strand. Specimens of the different qualities 3 or 4 inches long are exhibited to the seven or eight individuals who are the sole purchasers; and after being examined with a sharp instrument to ascertain the hardness, the choice is made, and the order given, the first choice being, however, accompanied with a higher price than the rest. But as there is no addition made to the quantity of black-lead during the year, it comes to pass, that at succeeding markets the specimens which had been previously rejected are all chosen in turn, until the whole is disposed of. There are several mines of plumbago in the United States of America, the most important being that at Sturbridge, Massachusetts. The plumbago thence obtained is in large masses, in veins, in gneiss, and is coarsely granular and foliated in texture. The quantity annually procured amounts to about 30 tons. At Taunton, Massachusetts, the Sturbridge plumbago is prepared by first pulverising it, and then, by machine pressure, condensing it into thin sheets. These sheets are then sawn up of the size required. This resembles the French method, by which graphite even of coarse qualities is made useful by being ground fine and calcined, but in this latter case it is mixed in a paste with very fine clay, and lamp-black is occasionally added. The purity of the English mineral enables the manufacturer to apply it to use by simply sawing out slender parallelopipeds, from 1 to 2 inches long, from sound pieces of plumbago which have been previously calcined in close vessels at a bright red heat. These parallelopipeds, enclosed in cases of cedar, form the best black-lead pencils. But they may be also used alone, being protruded as they are wanted from slender tubes, by means of an iron wire and screw contained in the new form of pencil case adopted of late years, and called the ever-pointed pencil. The cedar cases are made by cutting the wood with a circular saw into four-sided strips of a proper length, and these are arranged so that the thickness of two of them may form a square, of which one piece is thicker than the other, and is grooved by a common plough plane to receive the lead. This is first dipped in glue, and then adjusted to the groove, portion after portion, till the whole of the groove is filled. The surface is then smoothed down level, and the other half of the cedar is glued on, thus making a square black-lead pencil. To make this round, it is passed through a hole in an iron or steel puppet of the exact size of the pencil, and forced along by the workman. On the other side of this hole is an apparatus consisting of two gauges, and a small plane iron, revolving round an open centre, and cutting the pencil into a cylindrical form as it passes along towards a circular hole which next receives the newly fashioned pencil, and further compresses and polishes it before it is finally withdrawn by the workman with a pair of wooden nippers. To prepare the cylindrical leads for everpointed pencils is a work of much delicacy. The black-lead, first cut into square prisms, is ingeniously and gradually brought into the required form, by passing it through three different sized circular holes cut in pieces of ruby; the first converts the square into an eight-sided prism; the second changes the eight-sided to a sixteen-sided prism; the third converts it into a cylindrical form, and is of the exact size. The rubies in this operation do not last many days, and steel it is said is worn out in a few hours, so that the ever-pointed pencils, if genuine, can never be very cheap. Yet thousands of pencils resembling these, but made of composition instead of pure lead, are sold at an exceedingly low price. The first attempt at artificial pencils which led to any important results was that of a French gentleman, named Conté, whose process has been already alluded to. The admixture of pure clay in various proportions, not only with black-lead reduced to powder, but with different coloured earths, enabled him to produce various degrees of hardness and tint which were highly advantageous, and caused these pencils to become celebrated, and to yield to the inventor and his family a handsome fortune. The clay was first carefully washed and diffused in large tubs of river water, and allowed to settle two minutes, when the milky liquor was drawn off from near the surface into the second tub, which thus received only the finest particles. The sediment in this second tub is extremely soft and plastic, and when dried on linen filters, is fit for use. Meanwhile, the plumbago has been powdered in an iron mortar, and calcined in a crucible to nearly a white heat. It is then ready to be mixed with the clay in varying proportions, a fine hard pencil being produced by 2 parts clay to 1 part plumbago, a softer pencil by equal parts of each. The powders when mixed are triturated with water to a smooth paste, and ground with a muller on a porphyry slab till they are of the consistence of thin dough. This dough is pressed into grooves in a smooth board, (previousıy boiled in grease to prevent the clay sticking to it,) and another board screwed down upon it, so that the air can only act on the ends of the pencils in the grooves, which accordingly contract and become loose in the grooves. The mould is put into an oven at a moderate heat further to dry the pencils, which are then taken out and still further hardened by setting them upright in a crucible, having a luted cover, surrounding them with sand or charcoal powder, and placing them in a furnace, where they are baked more or less, according to the degree of hardness required, and when withdrawn are allowed to cool in the crucible. They are now ready for being placed in the cedar cases, but if intended for very fine work, (architectural drawing, for instance,) they must be first heated and then immersed in melted wax or suet, nearly boiling hot, before being fixed in the case. This gives them a certain degree of softness, and preserves their points better. The hardest pencils of the architect have, however, been made of lead melted with some antimony and a little mercury. common pencils sold in the streets of London are made with the powder of black-lead, mixed with melted sulphur, and poured into moulds which are sometimes reed or rushes. Common carpenter's pencils are of this sort and answer very well for the The purposes to which they are applied. Gum arabic and | several months' exposure to air, light, and moisture, resin are often mixed with the plumbago in common pencils. Besides the principal use of black-lead in making pencils, it is also employed for counteracting friction, for making crucibles and portable furnaces, and for giving a gloss to the surface of cast-iron. The inferior descriptions of plumbago are largely employed for these purposes. BLACKING. An article prepared in various ways for the blacking of boots and shoes. Each manufacturer has his own recipe, in which the principal ingredients are oil, vinegar, and ivory-black, or some other sort of blacking matter. In former days shoe-blacks stood in our streets to perform the required operation on pedestrians, but in these days of improved pavements, and greater cleanliness, the brilliancy of the shoe that has received its morning polish at home, is scarcely inpaired through the day. Blacking is either liquid or in the form of a paste, and some of the establishments for its manufacture, especially in London, are on the most extensive scale, and are known by their elaborate system of advertising all over the world. Among the various prescriptions for making liquid or paste blacking, the following, which has the title of "patent," is remarkable for the introduction of caoutchouc, which would tend to make the blacking water-proof:-18 ozs. of caoutchouc are dissolved in 9lbs. of hot rape oil. Add 60 lbs. ivory black, and 45 lbs. molasses, with 1lb. finely ground gum arabic previously dissolved in 20 gallons of vinegar of strength No 24. The whole to be well triturated in a paint-mill till smooth. Then add in small successive quantities 12lbs. sulphuric acid, stirring strongly for half an hour. The stirring to be continued for half an hour a day during a fortnight, when 3lbs. of gum arabic in fine powder are to be added, and the half-hour's stirring to be continued another fortnight. A fine liquid blacking is then produced, and is ready for use. To make paste blacking, the same ingredients and quantities are employed, except that the gum arabic is dissolved in only 12lbs. of vinegar instead of 20 gallons, and the paste is ready in a week. BLANKET. [See WooL and WORSTED.] the goods were bleached. Goods forwarded to Holland in the month of March were usually returned in the following October, but if sent at a later period, they were not returned until the autumn of the following year. The linens thus bleached were called Hollands, a name which they still retain. Many attempts were made to introduce the Dutch method of bleaching into this country. In 1749 bleach-works were established in the north of Scotland with tolerable success. The cloth was first steeped for some days in alkaline leys; it was then washed clean and spread upon the grass for some weeks. This bucking and crofting were repeated five or six times alternately. The cloth was then steeped for some days in sour milk, washed clean and again crofted. These processes were repeated until the linen was sufficiently bleached, the strength of the alkaline ley being gradually diminished. This method of bleaching was very expensive, not only from the length of time required in the operation, but also from the large extent of grass-land required in crofting. The constant exposure of large quantities of goods out of doors served as a temptation to dishonest persons, and led to much crime and to severe penal laws against the delinquents. Cases have also occurred in which innocent persons have been shot by spring guns or wounded by mantraps, and in one terrible case, a man who was watching his property actually shot his own son, who, after a long absence at sea, was returning home, and walked across the bleach croft as a nearer path to the house. The first improvement on the old Dutch method, was in the process of souring, in which dilute sulphuric acid was substituted for sour milk, the effect of which was to reduce the time required for bleaching, from 8 to 4 months; but the grand improvement in the art was made by Berthollet, who, in 1785, while repeating some experiments on chlorine, which had been discovered by Scheele in 1774, found that an aqueous solution of this substance was capable of destroying vegetable colours, and he was hence led to suggest its application to bleaching. In 1786, Berthollet showed the experiment to Watt, BLAST. [See BELLOWS and BLOWING MA- who was then in Paris, and on his return to England CHINES.] BLAST FURNACE. [See IRON.] BLASTING. [See MINE and QUARRY.] BLEACHING (from the French blanchir, to whiten). Calico, muslin, and other cotton fabrics which are sold in a white state, require bleaching, which is also often a preparatory process to dyeing and calico-printing. Linen goods also require bleaching. There is probably no department of the useful arts which has received such direct and obvious benefits from chemical science as the art of bleaching. It was formerly the practice to send all the brown linen manufactured in Scotland to Holland to be bleached. After some preparatory processes, the linen was spread out in bleaching grounds, and sprinkled with pure water several times a-day. In the course of he examined the subject practically, and actually bleached 1,500 yards of liren by its means, in the bleach-field of his father-in-law Mr. Macgregor, near Glasgow, who was so well satisfied with the process that he resolved to adopt it at his works. In the following year Professor Copeland of Aberdeen introduced the plan to the bleachers of that neighbourhood, who adopted it gladly. The method soon got into bleach-works generally, but it was found after a short time that the powerful action of the gas was injurious to the workmen, and also to the texture of the goods exposed to it. BertheHet endeavoured to remove the noxious odour by adding potash to the water, by which means a greater quantity of the gas was absorbed, and the solution was then diluted with a considerable quantity of within the chamber is stirred up by means of rakes water. The bleaching property of the solution was however destroyed after a time by this method, in from the outside, or a man enters the chambers consequence of certain chemical changes which took for the purpose by the doors kk: by this means the place. Dr. Henry of Manchester substituted lime particles of lime which have not yet absorbed the gas for the potash, by first passing the goods to be are exposed to its action. The process is then conbleached through a stratum of thin cream of lime, tinued for another 2 days, the materials in the leaden and then exposing them to an atmosphere of retort being frequently stirred up. When all the chlorine; a chloride of lime was thus formed in the chlorine is extracted, the contents of the retort, concloth, but its action was in some cases injurious. sisting of sulphate of soda and sulphate of mangaIn 1798 Mr. Tennant of Glasgow took out a patent | nese, are removed by the tube g. for a method of making a saturated solution of chloride of lime for bleaching purposes. It was perfectly successful, but the patent was set aside on the ground that the invention was not new. Mr. Tennant, however, continued his investigations, and discovered a method of impregnating lime in a dry state with chlorine, thus producing the celebrated bleaching powder, which is prepared at the present day much in the same manner as it was originally contrived. The lime is contained in a stone chamber i, (Fig. 137,) 8 or 9 feet high, built of siliceous sand Fig. 137. stone, the joints of which are secured with a cement of pitch, resin and gypsum. A door fitted into it at one end, can be made air-tight by strips of cloth and clay. A window at each side enables the workmen to judge how the impregnation goes on by the colour of the gas, which is yellowish green. The lime to be impregnated with the gas is contained in trays 8 or 10 feet long, 2 feet broad, and 1 inch deep. These trays are arranged one over another to the height of 5 or 6 feet, and are kept about an inch asunder by means of cross bars. The chlorine is obtained from common salt (chloride of sodium), by the action of black oxide of manganese and sulphuric acid. About 10 cwt. of salt are mixed with from 10 to 14 cwt. of manganese, and then introduced by an aperture at c into a large leaden vessel of a nearly globular form. This vessel has an outer casing or jacket of iron a a, and steam is admitted at h into the interval between the two, for the purpose of communicating heat. From 12 to 14 cwt. of sulphuric acid are introduced in successive portions through a twisted funnel ƒ, and the materials are all stirred up by means of an agitator db, the handle of which is on the outside. As the gas escapes from this vessel, it is received into a leaden cylinder containing water: it then enters by a leaden pipe e into the top of the ceiling of the stove-room i, and being heavier than the air of the room, falls slowly down and diffuses itself through the chamber, where it gradually combines with the lime. After the action has been carried on for about 2 days, the half formed chloride The chloride of lime thus formed, is used in enormous quantities in the bleach-works of Great Britain, most of which are situated in Lancashire and in the neighbourhood of Glasgow. As the various processes require an abundant supply of pure water, the works are usually situated near some stream. The substances which require to be removed from cotton goods in order that they may have a pure white colour, are of various kinds. The cotton fibres are covered with a resinous substance, which to a certain extent prevents the absorption of moisture, and also with a yellow colouring matter, which in some kinds of cotton is so marked as to give a distinctive character to the fabric made from it, as in nankin or nankeen, which is manufactured in China, from a native cotton of a brown yellow hue. Neither the resinous nor the colouring matter has any influence on the strength of the fibre, for the yarn spun from it is as strong after bleaching as before. In some varieties of cotton, the quantity of colouring matter is so small, that the fabric would not require bleaching were it not for the impurities acquired in spinning and weaving. The weavers' dressing of paste, and the rancid tallow or butter used to soften it when it becomes dry, certain soapy and earthy matters, and the dirt of the hands, all require to be removed. As soon as the goods are received at the bleachworks, the end of every piece is marked with the proprietor's name, which is done with a needle and thread, or with a wooden stamp moistened with coal tar. The fibrous down or nap on the surface of the goods is then burnt off by a process called singeing, which greatly improves their appearance, and in the case of dyeing or printing enables the cloth to receive the dye or pattern more perfectly. In this process a number of pieces of cloth are fastened together at the ends by means of long wires, and then wound upon a roller furnished with a winch. The cloth is then drawn over a half cylinder of copper made red-hot by being built into a horizontal flue (Fig. 138). As soon as the cloth has passed over the heated metal, it is wound upon a second roller which plays in a trough of water. The cloth is usually passed three times over the hot surface, twice on the face or the side intended for printing on, and once on the back. It is wound from one roller over the heated metal to another roller on the other side of the furnace, a swing frame being placed for raising the cloth at any moment out of contact with the heated metal, and water is at hand in case of accident to the goods, which is a rare occurrence. By this operation the goods become browned and discoloured. | equal compartments by partitions proceeding from the Gas flames are used for singeing thread, muslins, and bobbin-net lace. The flames issue from numerous perforations in the upper surface of a horizontal tube, Fig. 138. SINGEING COTTON GOODS. and the fabric to be singed is drawn over the flame upon rollers with a rapidity adapted to the texture of the goods. The flame is drawn up through the web by placing immediately over the gas-flame a horizontal tube with a slit in its lower surface. This tube is connected with a fan or other apparatus for withdrawing the air from it, and thus increasing the draught of the flame. After singeing, the cloth is steeped in a cistern of water, and, in order to ensure contact with the water, each piece is pulled out, folded loosely, and tied up, with a noose at the end, into an irregular axis to the circumference, each of which has a circular Fig. 140. the fire acts, and an upper part of cast-iron for containing the goods. The two parts are separated bundle. After soaking 12 or 14 hours, the pieces are washed in a dash or wash-wheel, which is a hollow, circular, perpendicular wheel, 5 or 6 feet in diameter, and nearly 2 feet in depth. It is divided into four Fig. 141. BUCKING KEIRS. The by a false bottom of cast-iron, and in the centre is |