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and is gradually spread over the goods as they are deposited in layers in the keir; the requisite quantity of water is next added, and heat is applied. The liquor is about two hours in boiling, and the process is continued for about seven hours. The effect of the lime is to darken the colouring matter of the cotton, so that after washing they appear darker than they did before; but all the dirt and grease are removed by this process. The goods are next washed in the dash-wheels, in order to remove the adhering lime, and then comes the chemicking, or steeping in a very dilute solution of chloride of lime, for which purpose they arc placed in stone vats, over the centre of which is a perforated trough, into which the bleaching solution is pumped up many times during the process, and from this it drains down upon the goods. Every pound of cloth requires about half a pound of chloride of lime, of a certain strength, mixed with about three gallons of water. The steeping is continued six hours, after which the cloth is of a light grey colour, not white, but considerably improved in appearance. Care must be taken to make the steep of the proper strength, for if too strong, the calico will run into holes.
In the next process, which is called souring, the goods are steeped for four hours in water soured by sulphuric acid, when a minute disengagement of chlorine takes place throughout the substance of the cloth, and it immediately assumes a bleached appearance. The acid also removes a small portion of oxide of iron contained in the fibre, and also the lime of the previous processes. When removed from the acid, the goods are again washed: they are greatly improved in appearance, but still not quite bleached. They are therefore boiled for eight or nine hours in a potash or soda ley; then washed at the dash-wheel; again steeped for five or six hours in a solution of bleaching-powder, two-thirds of the strength of the first solution; then soured as before for two, three, or four hours, according to the quality of the goods, and at length they are perfectly bleached. Every trace of acid is removed by careful washing, for if any acid were left in the cloth, it would corrode it, especially when heated. The acid favours the bleaching action, and does not injure the fibre of the cloth, although the steeping is continued for days, provided the cloth is not allowed to dry with the acid in it, or be left above the surface of the liquor. The acid is also necessary to remove the caustic alkali, which adheres with great pertinacity to the goods. The goods lose weight in being bleached. Fine calico loses nearly 10 per cent.; but of this, one-half is the weavers' dressing. In coarse goods the loss is greater. For the processes subsequent to bleaching we must refer to the article Calendering.
The above details refer chiefly to cotton shirting, and the better descriptions of calico used for printing on. The processes are modified for different varieties of cotton goods. It is also often necessary to expedite the various processes. As an example of the rapidity of bleaching by the new method, compared with the old, wo may mention one case in which a
Lancashire bleacher received 1,400 pieces of grey muslin on a Tuesday, and on the Thursday following they were returned bleached to the manufacturers, at the distance of sixteen miles, and were packed up and sent off on the same day to a foreign market.
In bleaching linen, the processes are similar to those already given, but are continued longer on account of the firmer hold which the colouring matter has on flax. This colouring matter does not appear to be chemically combined with the fibre until the plant is steeped in water, in the process of retting (flax). Hence, to save the expense of bleaching, it has been proposed to separate the woody fibre by drying the plant, instead of steeping it, and then to beat off the woody parts by means of mallets. The linen can then be bleached by a simple washing in water.
In all these processes the efficient bleaching agent is the chlorine, but the precise method in which it acts is not well understood. Perfectly dry chlorine does not bleach at all; but when dissolved in water, its bleaching power seems to arise from its decomposing a portion of the water, the oxygen of which unites with the colouring matter, and renders it soluble in water or a weak acid solution. The bleaching power of dew and of rain-water is referred to the excess of free oxygen which they contain. But according to another view, the organic colouring matters being compounds of carbon, hydrogen, oxygen, and sometimes nitrogen, the chlorine acts directly upon them with decomposition, uniting with the hydrogen to form hydrocldoric acid, and setting the other components free, or rendering them soluble. For example, writing-ink is a compound of sesquioxide of iron and an organic substance named tannin. The cldorine will combine with the tannin or one of its elements, and cause the written characters to disappear. If the paper be now moistened with a solution of prussiate of potash, it will unite with the sesquioxide of iron, and the characters will reappear. If, however, after the tannin has been removed by the chlorine, the paper be washed over several times with very dilute hydrochloric acid, the writing will be completely destroyed. Chlorine has no action on Indian ink or on printer's ink, because the colouring matter in these cases is minutely divided carbon, which does not combine directly with chlorine.
Bleaching powder varies greatly in strength, and it is of importance to the manufacturer to be able to determine its value, or the quantity of chlorine contained in a given sample. Many methods have been recommended for this purpose. Professor Graham's method is simple in practice, and depends on the effect of the chlorine of the bleaching-powder in peroxidizing a proto-salt of iron, of which two equivalents require one of chlorine. The cldorine acts by decomposing water, and liberating a corresponding quantity of oxygen. 78 grains of green sulphate of iron are dissolved in about 2 ounces of water, and acidulated by a few drops of sulphuric or hydrocldoric acid. This quantity will require for peroxidation exactly 10 grains of chlorine. 50 grains of the bleachingpowder to be examined are next rubbed up with a little tepid water, and transferred to an alkalimeter, [see Alkalimetry], which is filled up to zero with water, and the contents well mixed by agitation. "The solution of chloride of lime being thus made up to 100 measures, is poured gradually into the solution of sulphate of iron, till the latter is completely peroxidized, and the number of measures of chloride required to produce that effect observed. The change in the degree of oxidation of the iron solution is discovered by means of red prussiate of potash, which gives a precipitate of prussian blue with a salt of the protoxide of iron only, and not with a salt of the peroxide. By means of a glass stirrer, a white stoneware plate is spotted over with small drops of the prussiate. A drop of the iron solution is mixed with one of these after every addition of chloride of lime, and the additions continued so long as a deep blue precipitate is produced. The liquid may continue to be coloured green by the iron salt, but that is of no moment. The richer the specimen of chloride of lime is in chlorine, the fewer measures of its solution are required to peroxidize the iron, the number of measures containing 10 grains of chlorine always producing that effect. The quantity of chlorine in the 50 grains of bleaching-powder is now known, being ascertained by the proportion, as the number of measures poured out of the alkalimeter is to 10 grains of chlorine, so 100 is to the total grains of chlorine. In a particular experiment, the 78 grains of sulphate of iron required 72 measures of the bleaching solution. Hence, as 72 is to 10, so 100 is to 13.89 chlorine in 50 grains of the chloride of lime. The quantity of chlorine in 100 grains of the chloride, or the per centage of chlorine, is obtained by doubling that number, and was therefore in this instance 27.78 per cent. or 28 per cent."'
According to Professor Brande, "the best samples of commercial chloride of lime contain on the average not more than 30 per cent. of chlorine, and when chlorine is passed over hydrate of lime, in an experiment upon the small scale, it cannot be made to absorb more than about 40 per cent.; but if the hydrate of lime be diffused through water, it will then absorb more than its own weight of chlorine, and we form a solution containing one equivalent of lime (or of hydrate of lime) and one of chlorine, which is the true atomic compound, and is dissolved out of bleaching-powder by the action of water."'
The bleaching of wool is performed by a process called sulphuring, in a close apartment in which sulphur is burning. The goods are hung on poles, so disposed that the sulphurous acid can readily penetrate them. When the chamber is filled, a quantity of sulphur is placed in flat broad dishes, and, being ignited, it is allowed to burn away gradually, and in the course of some hours the colouring matter is destroyed. In bleaching mousselins de laines (which are formed of cotton and wool), the goods are usually passed two or three times through
(1) Graham's " Elements of Chemistry."
a solution of soap and soda at about the temperature of 130°, and then sulphured for several hours. After this they are passed through a very weak solution of caustic soda, dried, and usually impregnated with a dilute solution of tin, which imparts considerable brilliancy to the colours afterwards applied to the goods.
Other varieties of bleaching will be noticed under the articles, Paper, Silk, Wax, &c.
BLENDE. The native sulphuret of zinc, called by the miners black-jack. [See Zinc]
BLOCK. A block is a pulley or sheave, revolving on a fixed axis or pin within a chamber or mortice, cut out of a solid block of elm, ash, or other tough wood, which is called the shell. The sheave is a circular piece of wood, usually lignum vita;, but sometimes of brass or cast metal, with a groove on the edge for the reception of the rope. In the best blocks, called conked sheaves, the sheave has a brass bush fitted in the centre, with a hole through it for the pin, as in Fig. 142. The pin is usually of iron, but sometimes of lignum vitae, or other hard wood. It is supported by passing through the sides of the shell. Some blocks are made Fig. U2.
to accommodate 2, 3, and even 4 sheaves, in which case there are as many separate mortices. If the sheaves are placed side by side the same pin serves, but if placed one above the other, then of course there arc separate pins. In nautical language the block with its rope is called a tackle of single or double blocks. Each block is furnished with a band or strap, terminating in an eye of rope or an iron hook, for attaching it to an object on which it is intended to act as a mechanical power, while another block is suspended from some fixed support. The former is called a running block, and the latter a standing block. The shells of very large blocks are made up of separate pieces strongly bolted together; these are termed made blocks. Blocks are also termed thick or thin, according as they are adapted to the reception of large or small ropes.
Blocks are chiefly employed in the rigging of ships, to assist in raising or lowering the masts, yards, and sails. They are also available as a mechanical power under a great variety of circumstances. There is a description of block without sheaves, termed deadeyes, used for setting up and fastening shronds, and other standing rigging, sheaved blocks being chiefly used for the running rigging.
It would be quite impossible within the limits of this article, even if it were desirable, to describe the various forms of blocks used in the navy. A few, however, may be noticed. Fig. 143 is called a snatchblock. It consists of a single sheave, with a noteh cut through one of the cheeks, to allow the rope / to be lifted in and out of I the block without putting its end in first. In this example, the strap does not surround the block, but is put through a hole at one end. This is a convenient block for nauling a rope.
In Fig. 141 the block is iron-bound, terminating at the notehed end in a swivel hook or an eye-bolt large enough to receive several turns of lashing, by which the block is attached to the fixed support. Fig. Im. That part of the strap over the
noteh in the side lifts up with a hinge, and is confined down when the rope is in the block by a small pin passed through an eye in the hinge part of the strap. The strap at the other part of the block is let into the wood, and is kept to its place by nails. This block is used where a warp or hawser is brought to the capstan.
Fig. 145 is a long tackk block, consisting of
two single sheaves, one
above the other in the
same block. The lower
one is § the size of
fig. 14i. the upper; and is used
in combination with a common single block to form
long tackle for loading or any other purchase.
Fig. 146 is a clue garnet block with a single sheave. This is susf's- 146. pended from the yards
by a strap with two eyes, and a lashing surrounding the yard, and passing through the eyes. These blocks receive the clue garnets, or ropes which haul up the clues of the sail, and are applied to the main and fore-yards. Clue-line blocks serve the same purpose, but are applied to the top-sails, top-gallant, and sprit-sails. These blocks were improved, by Brunel. In the old form the rope had a tendency to get entangled with the sail, and to slip out of the groove of the sheave. In the improved block two holes are made for the purpose of passing the rope in and out. The sheave is in the centre of the block, so as to be entirely inclnded, except the mortice, where the sheave is put in. The strap surrounds the lower part of the block, and both ends of it pass through the hole in the upper part, where they cross each other; they are then formed into an eye, by which the block is suspended from the yard. In this arrangement the parts cannot get out of place, as the garnet or rope is so much confined within the block, nor can the sail be driven into the block as in the old form.
Fig. 147 is a shoulder block. A large single block left nearly square at the upper end, and cut sloping in the direction of the sheave. It is used on the lower yard-arms to Fig. U7. lead in the top-sail sheets, and
on the top-yards to lead in the top-gallant sheets, which by means of the shoulder are kept upright, and prevented from jamming between the block and the yard.
which a spiral spring is linked at one end by a hook, and at the other by a ring, which is to be annexed to an eye-bolt at the timber head or other point of application. Two of these blocks are used, one to the timber heads, and the other to the sail. Passing through the spirals of the spring chain is another chain called the check chain, which is connected by links to the hook and to the ring, to prevent the spring being drawn out too far, and thus damaged. Vessels provided with these spring blocks are less liable to heel, and will receive the impulse of the wind to better advantage, but the plan does not seem to have been adopted to any great extent.
Among the forms of block used in the navy, some are named after their shape, as D blocks, Sioe-blocVs, Nine-pin blocks. Others are named from a family likeness, as sister-hlocVs, which are two similar single blocks formed out of one solid piece.
Before the introduction of machinery blocks were made in the following manner:—The shells were sawed to the proper length and thickness; the corners were then sawed off; the workman then gauged or marked out the size of the mortice or sheave-hole in the middle, -j^th larger than the thickness of the sheave. In single sheaved blocks the thickness was larger than the diameter. In blocks of two or more sheaves the partitions between them were £th less than each mortice. The block was then jammed up edgewise in a frame, and the mortices gouged out with an auger, and the wood sawed out with a rib saw. The holes were further cleared out by chisels and by burrs at the corners. The pin-hole was next bored through the middle ^th less than the diameter of the pin. The outsides and edges of the block were then rounded off by shaves. The scores or grooves for receiving the strap were made, and the sheaves were then fitted. These were Vs-th thicker than the diameter of the rope intended to run on them, and 5 times that thickness in diameter. The sheave being nicely bored was put into the lathe and turned smooth, and the groove on its circumference was hollowed out to a depth equal to |d of its thickness, so that the rope might embrace it closely. The diameter of the pin was that of the thickness of the sheave. The pin was turned cylindrical, except the head, which was left octagonal to prevent it from turning in the block. After the sheave was fitted by driving the pin through the block and sheave, one end of the block was hollowed out to admit the rope, and a small neat chamfer was taken off the edges. The whole block when finished usually formed an oval spheroid flattened at the opposite sides.
The manufacture of an article apparently so trilling as that of a ship's block, seems scarcely to require the assistance of much machinery, or to entail any very great expense on the country; but when it is considered that a single 74-gun ship requires not less than 1,270 blocks, besides 160 dead eyes, and other small articles of a similar kind, all absolutely necessary to the working and even to the safety of a ship, it will readily be supposed how difficult it must be to maintain the supply if made by hand, and how great the expense. The immense demand for blocks during the long protracted war, had called the attention of the Admiralty and Navy Board to the possibility of making some reduction in the expense of this important article. About the year 1801, Mr. M. I. Brunel, an ingenious mechanic from America, had completed models of certain machines for the construction, by an improved method, of the shells and sheaves of blocks. This model was submitted to the Lords of the Admiralty, and by them referred to General Bentham, the Inspector-general of Naval Works. The advantages of machine-made blocks were stated to be, first, in ensuring regular and determined dimensions; secondly, in adding strength where it was wanted, by making the head and bottom more substantial, and less liable to split; and thirdly, in leaving the wood between the two mortices thicker, so as to admit a sufficient bearing for the pins. The uniformity and exactness with which these blocks were to be made would also make it difficult to counterfeit them, and this would act as a precaution against embezzlement. Another great advantage would be the using up of much waste wood in the dockyard, usually sold for a trifle for fire-wood, &c. The sheaves would also be made so true to each other, that every sheave of any particular size would equally fit any shell of the size for which it was intended; and the inconvenience to which ordinary blocks are liable from the friction of the ropes against one or alternately both of the sides of the mortices, was to be removed by placing a sheet of metal on the upper part of the mortice, bent to the proper shape by an engine adapted to the purpose.
General Bentham reported that by the new method there would not only be a great saving, but also an increase of strength, durability, and facility of working in the new blocks. Accordingly, those parts of the machinery which had been secured by patent were removed to Portsmouth in 1804, and were put in operation, while other machines necessary to the completion of the whole scheme were at work by 1808. From that time to the present the whole has gone on without any alteration or assistance from the inventor, and is so complete in all its parts that the attendance of a few common labourers under the direction of the master of the wood-mills is quite sufficient. This collection of machines is one of the most ingenious and complete that was ever invented for forming articles in wood; so that not only blocks, but other articles in wood can be produced, the machines performing most of the practical operations of carpentry with the utmost accuracy and despateh.
The largest timber can be converted and sawed up into any scantling, by several circular and reciprocating saws adapted to various purposes. Some of the operations performed by the smaller machines are boring, mortising, turning in wood and iron, riveting, drilling, broaching, burnishing iron pins, &c., operations which were formerly supposed to be chiefly or entirely dependent on the skill and dexterity of the workman. These machines are set in motion by a steam engine of 32-horse power, which is also used for various other purposes in the dockyard. Under this system 4 men can do the work of 50 in making shells, and 6 men can do the work of 60 in making sheaves. These 10 men thus displacing 110 can easily finish in one year 130,000 to 140,000 blocks of different sorts and sizes, of the value of 50,000/., this being the average annual number and value from the year 1808 to the conclusion of the war. Brunel was engaged in completing this system from September 1802 to June 1808, his allowance during that time being 1 guinea a day. On the completion of the system it was agreed that the savings of one year as compared with the contract prices was a fair remuneration. These savings were estimated at 16,621?., to which we may add the six years' allowance at 1 guinea per day, amounting to 2,400/., and for the working model 1,000/., making the total amount reoeived by Brunel about 20,000/., a very fair and moderate remuneration, especially when it is considered that the expenses of the buildings for the new machinery, the machinery itself, the steam-engine, the interest of money, were all completely cleared off by the savings of four years. Such was the importance attached by the government to this invention, that a complete set of duplicate machinery was erected in the Dock Yard at Chatham, and kept in constant readiness for action in case of any accident to the machinery at Portsmouth. Hitherto, however, the duplicate machinery has not been wanted.
The machinery was constructed by Mr. Mandslay, of the Westminster-road, London. The framing of the machinery was of cast-iron, and those parts exposed to violent and rapid motion were of hardened steel. The writer of the article in Rees's Cyelopaedia, in which this machinery is minutely described, in speaking of its excellent construction, remarks, that "well-constructed machinery, though expensive in the erection, is cheaper in the end than imperfect works, which require constant repair, the expense of which is the least evil; as it generally happens that a machine will fail at that time when it is most wanted, in consequence of being then most worked; and the loss occasioned by the stoppage of great works, particularly where many people are employed, is too evident to require notice. In the same manner, an attention to neatness in the appearance of machinery has its advantages, by inducing the workmen to be careful of the machines they work at, to preserve them from the slightest injury, and to keep them clean from dust, which, trifling as it may appear, is a very essential point in the preservation of those parts which are in rapid motion, with friction against other parts, for dust getting between such surfaces grinds them away very fast, and in their most essential points."
We will now notice the machines, and the operations connected therewith, referring to larger works for a more detailed description.1
1. The straight cross-cutting saw. This is used for cutting up into lengths the elm-trees, of which the shells of the blocks are to be made. The log is introduced through one of the windows of the woodmill upon a very low bench below the saw, which is lowered, and made to rest with its teeth upon the log, the back being retained in the cleft of the guide. When the crank is set in motion, the saw moves backwards and forwards, exactly as if worked by hand, and quickly cuts through the tree. After the saw has cut to some depth it gets out of the guide, and is sufficiently deep in the wood to guide itself, for in cutting across the grain of the wood it has no tendency to move out of the true line. When the saw has cut off a piece from the log, its handle is caught by a fixed stop, the machine is thrown out of gear, a man lifts up the saw by a rope, and the block is advanced to receive a fresh cut. This saw is used for the largest trees only.
2. The circular cross-cutting saw, used for the smaller trees. The axis of this saw is parallel to the length of the tree to be cut; but is so mounted that it can be moved in all directions, cither raised up or moved aside; but in all these motions its axis continues parallel to itself, and the saw continues in the same plane. These motions are produced by two winches, each provided with a pair of equal pinions, working a pair of racks fixed upon two long poles. The spindles of these winches are fixed in two vertical posts, which support the axis of the upper frame. One of these pairs of poles is jointed to the extreme end of the upper frame, so that by turning the handle belonging to them the frame and saw are raised or lowered. The other pair of poles is attached to the lower part of the saw frame, so that the saw can be moved sidewise by means of their handles, which then swing the saw from its vertical position. These handles give the workman complete command of the saw. By means of one of them he draws the saw against one side of the tree, which is properly secured, and cuts it about half or one-third through; by the other handle he raises the saw up, draws it against the top of the tree, and cuts it half through from the upper side; he then depresses the saw, and cuts it half through from the next side; and lastly, a trifling cut at the lower side separates the block, and the tree is then advanced for another cut.
3. The reciprocating ripping-saw cuts these blocks in the direction of the grain into two, three, or more pieces, in one direction, and then in a direction per
(1) The reader interested in the subject is referred to the 22d Tolume of Rees's Cyclopaedia, and also to the Sd volume of Brewster'* Edinburgh Cyclopaedia. To the latter authority we are indebted for the description of the illustrative figures of the machines numbered 5 to 9.
pendicular to the former, so as to reduce the logs to the size of the required blocks. The aetion of this saw is similar to that of No. 1.
4. The cireular ripping-saw, for smaller sizes than No. 3. This is a thin disc of steel . with teeth formed in its periphery: it is fixed to a horizontal axis just below the surface of a bench, so that a portion of the saw projects through a slit a few inches above the bench. A rapid rotatory motion is given to it by a strap passing over a pulley at the further end of the axis. The workman places the block with one side flat upon the bench, and sliding it forward against the saw, it is cut through with great precision and rapidity.
5. The blocks having been cut to the proper size by the saws, are placed in the boring-machine, Fig. 149. This machine has an iron frame A A, with three
/'',</. 149. THE BoRlNO MACHINE*
legs, between which the block is introduced, and the screw B being foreed down upon it, confines it to the proper place for the borers D E to act upon it. The end of the screw B has a steel ring fitted upon it, the lower side of which is a sharp edge. When the screw is whirled round, the balls at the end of its cross handle cause it to act as a fly-press, to stamp the impression on the end of the block. The exact position of the block is ascertained by a piece of metal, (Fig. 150,) fixed just beneath the point of the borer E. This piece of metal adjusts Fig. iso. the position for the borer D, and its height is regulated by resting on the head of the screw x, which fastens the piece x down to the frame. The sides of the block are kept parallel by being applied against the heads of three screws, represented by dotted lines, in the double leg of A. The borer D bores the hole for the centrepin; the borer r. makes the holes for the commencement of the sheaveholes. The borers are of the same form as a carpenter's centre-bit, and each is screwed upon the end of a small mandril mounted in a lathe-frame G and H. These frames are fitted with sliders upon the edges of the flat bars i k, the former being secured to tho