Vickipedia

REAPING, the act of cutting corn, has been performed from . time immemorial with an instrument called a reaping-hook or sickle. The sickles in use among the ancient Jews, Egyptians, and Chinese appear to have differed very little in form from those employed in Great Britain. The reaping-hook is a curved instrument of about a foot and a half in length, tapering from a breadth of about two inches at the but-end, where it is fixed into a wooden handle. The edge is sometimes serrated, but, as a rule, it has long been made plain and sharp like a knife. In reaping, the harvester takes the corn in his left hand, and then with the hook cuts the stalks as close to the ground as possible; but when a grass crop has been sown down with the grain, the stubble is often left rather longer, in order to preserve the young grass The corn is placed handful by handful in a band usually made of the corn, and when as much has been cut as will form a sheaf, it is tied up by the ‘ bandster.’ The most expert reapers slash down the corn with the hook in the right hand, using the left merely to keep the corn from falling, until sufficient to make a sheaf has been cut, when the reaper places his hook under the corn, and supporting it with his left arm, deposits it all at once in the band. A bandster (one to every three or four reapers) binds the grain, and sets it up in stocks of generally 12 sheaves. It was surprising to see women of sixty years and upwards, handling the ‘ hook ‘ with great dexterity, accomplishing their 20 and sometimes 24 stocks of 12 sheaves each per day. After such a day’s work, these women appeared much fatigued, but a night’s rest seemed to set them on foot, vigorous as ever. They divested themselves of much of their clothing, and really worked hard for their money.

In the principal corn-growing districts of Scotland, a great proportion of the reaping by hand was at one time done by laborers from Ireland, who undertook the work at from 8s. to 15s. per acre, with board and lodging in addition. Their fare was of the simplest kind—consisting in the majority of cases, of porridge morning and evening, and bread and beer for dinner; their lodging at night was the barn or some outhouse, the farmer providing coarse blankets for covering. The quantity of porridge consumed at each meal by those people was sometimes astonishing—no less, as has been proved by actual weighing, than 5 lbs., with 1 ½ lbs. of milk besides. In England, most of the corn was cut by piecework, at prices varying from 10s. to 18s. per acre. On the stronger lands of the midland and southern counties, the stubble is some-times left knee-high, and afterwards at leisure cut by the scythe, or with a long hook, at a cost of 2s. per acre. In Yorkshire, Derbyshire, Oxfordshire, and on many of the lighter soils in other counties, the operation of fagging or hacking, to be afterwards noticed, was preferred as being more expeditious than reaping. A good hand cut down from one-third to one-half of an acre of wheat, and often consumed, during his long day’s labor, two gallons of good ale.

The scythe in some counties, more than thirty years ago, was preferred to the sickle. The most common varieties were: the Hainault scythe—an importation from Belgium—the cradle scythe, and the common scythe fitted with a cradle. The Hainault scythe consists of a blade about 2 feet 3 inches long, having a handle 14 inches long. This the mower holds in his right hand, while in his left he carries a hook, with a handle of about equal length. ‘The reaping,’ says the late Mr. Henry Stephens, in his Book of the Farm, ‘is done by pressing the back of the hook with the left hand against the standing corn, in the direction of the wind, and by cutting with the scythe close to the ground against the standing corn with a free swing of the right arm,’ the hook keeping the cut corn from falling until a sufficient quantity to form a sheaf has been cut. This operation was practised in many parts of England, and especially on the lighter soils, under the name of fagging or hacking, the reaper sometimes using in his left band. instead of the hook, a stout crooked stick from 2 1/2 to 3 feet long. Beans and oats were the crops most generally fagged.

The cradle scythe is composed of a blade about 3 1/2 feet long, attached to a principal helve or sned about 4 feet long, into which another helve of about 2 1/2 feet in length is tenoned, thus making two handles. The cradle or bow is a piece of wood joined to the heel of the blade, into which are inserted three or four wooden teeth, in a line with the blade, the object of which is to secure the grain being laid evenly in one direction. As skill at the working of the scythe, however, increased, the cradle or bow was discarded in many cases. By the scythe, corn can be cut at a rather less cost per acre than with the hook; but the work is not so neatly done. As nice a stubble will be left by a good hand with the scythe, and often nicer than by the hook, but the sheaves are not, as a rule, so tidy after the scythe, though they will stack rather earlier. Of a fair working crop, an adept at the scythe would cut 2 or 2 1/4 acres per diem. The average area cut per day with the scythe does not exceed 1 1/2 acres. In fact, if the crop is heavy, that extent is a very hard day’s work. Those who contract for cutting the crops by the scythe, obtain the services of the best men, and thus generally get about 2 acres per day reaped, and reaped very well too. In the midland and southern counties, of England, the scythe, long in general use, was of larger size, and had only one long shaft, on which were fixed two handles. In Bedfordshire, Hertfordshire, and some of the eastern counties, the whole of the cutting, until the introduction of reaping-machines, was done by these scythes. The harvest operations then, from the cutting of the crop to the thatching of the ricks, cost from 18s. to 25s. per acre.

The process of reaping with either the sickle or the scythe is, however, both tedious and expensive; and hence, during the last three-quarters of a century, many attempts have been made to accomplish the work by machinery—attempts which, in the course of the last twenty years, have been crowned with complete success ‘ Reaping by machinery, however, is no modern invention. Pliny the elder, who was born in the 1st c. of the Christian era, found a reaping-machine in Gaul. He says : ‘ In the extensive fields in the lowlands of Gaul, vans of large size, with projecting teeth on the edge, are driven on two wheels through the standing corn by an ox yoked in a reverse position. In this manner the ears are torn off, and fall into the van.’ Palladius, about four centuries later, found a similar appliance for reaping corn in Gaul. He gives a more detailed but similar description of the machine. The annexed cut, copied from Mr. Woodcroft’s Appendix to the Specifications of English Patents for Reaping-machines, represents what is conceived, from the descriptions, to have been the form of this ancient reaper.

In modern times, the idea of a mechanical reaper appears to have originated with a Mr. Capel Lloft, who, in 1785, suggested a machine something after the pattern of the ancient one above described. Between that time and the Great Exhibition of 1851, in London, from which the general use of mechanical reapers may be said to date, the patents taken out for reaping-machines were very numerous. Among the most promising of these may be mentioned those of Mr. Gladstone of Castle-Douglas; Mr. Smith of Deanston; Mr. Kerr, Edinburgh; Mr. Scott of Ormiston; Mr. Dobbs, an actor in Birmingham; Mr. Mann of Raby, near Wigton; and the late Rev. Patrick Bell of Carmylie, Scotland. In 1826, Mr. Bell constructed an efficient and simple machine, which long continued in use, and several features of which are observable in the reapers of the present day. The inventor of this, the first machine of the kind in Scotland, received a public testimonial from agriculturists, in consideration of the services he thus rendered to agriculture. In America Mr. Hussey and Mr. M’Cormick took out patents for reaping-machines of superior character in 1833 and 1834 respectively.

The movements of the cutters of these machines were various. A few were advancing only, some sidelong and advancing, others reciprocating and advancing, a large number continuous and advancing, and others continuous and alternate. The reciprocating and advancing motion is that now employed on the machines in use. The principal difference in the machines now so largely used for cutting corn is in the form and character of the cutters, and in the mode of delivering the grain after it is cut.

The cutting-knives are of two kinds—one, obtuse-angled and serrated; the other, acute-angled and for the most part plain. Both are attached to a bar, and are made to-work through another bar of iron fitted with hollow fingers, called guard-fingers, which, projecting forwards, catch the standing corn, and retain it firmly until it is cut. The serrated knife saws through it; the plain knife clips it, as it were; the finger-guard forming the fixed blade of the scissors.

The delivery of the sheaves is effected either by manual or mechanical labor; but the vast proportion of the machines in use are what are termed manual delivery-reapers. The delivery of the sheaves by manual labor is now almost at the back of the machine, the side delivery being generally abandoned, unless in the self-deliveries. In delivering the grain, a man, with a short-handled rake in his hand, sits upon the machine almost opposite the cutting apparatus. With this he inclines the grain towards the knife; and when sufficient to make a sheave has been cut, he rakes it off the platform upon the machine, on to which it has fallen, and deposits it on the ground. The cut subjoined will illustrate the method of raking off. In making a neat and squarely-formed sheaf, the raker is greatly assisted by a hinge in the platform, which enables him, by pressure of the foot, to tip the board over, so as to let the corn slide gently down.

With the back-delivery, the sheaves must be tied up and removed out of the way of the machine before it comes round again. Such a reaper, therefore, always requires a full supply of hands to attend upon it. But it is the best for all that. It does require a skilful, careful man to ‘ tilt,’ but the fact that the course has to be kept clear for the horses every round, spurs the laborers, who thus do more work than they would otherwise accomplish. Besides, it is a very doubtful advantage to be enabled to slash down the crops irrespective of the gathering capacities. Moreover, with the self-deliveries, it is the distance gone over, and not the quantity of crops collected, that regulates the size of the sheaf. With uneven crops, this is an inconvenience. Sheaves of different sizes are very troublesome in the stock. They will not stand well, and in stacking it is difficult to keep uniformity in building. Large and small sized sheaves are not equally dried, and are not ready for stacking at the same time. Eight people ‘ lifting’ after the manual-reaper will do as much work as nine following the self-delivery, so that the saving of a man’s labor claimed by the self-delivery is doubtful. The sheaves are rather better formed by the manual machine than by the self-delivery. Each kind, has, however, and will likely continue to have its advocates, though the preponderance is in favor of the manual.

The mechanical or self-delivery machines, as they are generally called, are of two kinds—one lays the cut corn in swaths, the other deposits it in sheaves. The latter is decidedly the best and most fashionable of the two.

The automaton sheaf-deliverers best known to the public are those of Samuelson of Banbury; Hornsby and Son; Burgess and Key; Brigham and Bickerton, Berwick; Howard and Co., Bedford. We give a description of Samuelson’s sheaf-deliverer (largely used in Great Britain), which will be made plain by the accompanying cut. The self-delivering machinery consists of a series of four rakes—two toothed, and two plain—attached to an upright shaft, in such manner as to admit of a free ascending, descending, and horizontal motion. The two toothless rakes, or ‘ dummies,’ are shorter in the arms by six inches than the other two, and are merely employed to incline the grain towards the cutter. The platform upon which the grain fails after it is cut is of quadrant shape, and is surrounded, on the outer edge, by a rim of about a foot deep. The side of the earn next the platform is bent or depressed, so that the rakes on reaching this point, make a sudden fall, or eccentric motion, thus assuming the horizontal attitude necessary to sweep over the platform on the level. The rakes are adjusted so as to lay the sheaves about 12 feet apart, to the side, and out of the way of the horses. This machine has a, double-throw knife—an arrangement which reduces the driving speed, and consequently the wear and tear of the machinery.

In M’Cormick’s automatic delivery-machine, a rake is so used that ‘during one part of the revolution of the gathering-reel, it acts as one of the vanes of the reel in bending the standing corn to the cutting-blades. When the rake reaches the cutting-blades in front of the platform, it ceases to revolve around the reel-shaft (which continues its rotary motion), and is made to move horizontally upon a vertical hinge, to which one end is attached (the points of the teeth being near the surface of the platform), sweeping the cut corn off at the side, and depositing it on the ground in sheaves ready for the binder.’ The Messrs. Brigham and Bickerton’s improved machine has a deep upright board of sheet-iron to keep the corn on the platform. Iron rods on these sheets separate the corn. This firm has thrown off two branches lately. The first offshoot was Messrs. Lillie and Elder, and the last was Bickerton and Co. The three firms make good serviceable reapers. Howard and Hornsby’s reapers are substantially and simply constructed, embracing slight improvements every other year, formed on experience. Prices range from £20 to £35.

The makers of manual delivery-machines are numerous, including in a prominent degree Kemp, Murray, and Nicholson, Stirling; Jack and Sons, Maybole; Harrison, Macgregor, & Co.; Picksley, Sims & Co.; Ransome, Sims and Head, Ipswich; Sam-nelson & Co., Banbury; J. and F. Howard, Bedford; and many others of fame. The manual delivery-machines of the first named firm are very popular, strong and ingeniously manufactured, while those of the Maybole firm are not quite so strong, but work with great ease and tastefulness. Carefully handled, the manual delivery-reaper will take up laid and twisted crops admirably. Indeed, all the reapers nowadays, perfected as they are year by year, now do their work remarkably well, leaving a beautiful stubble and a nice sheaf. The sheaves from the reaper, however, are not so easily dried for the stackyard as those from the scythe, but they defend rain better, and are altogether preferable. The number of reapers now in use in Great Britain is enormous, and is growing rapidly every year. They are a most decided improvement. Indeed, they are one of the most valuable introductions that have been made in rural agriculture in this country. At almost every farm of ordinary or even comparatively small dimensions, there is a reaper, and three or four engaged on the larger holdings. The cost of the manual delivery ranges from £18 to £30.

The cost of reaping by machinery is much less than either by scythe or sickle. Mr. Wilson of Woodhorn, Morpeth, found that the cutting of wheat with the sickle (binding and stocking included) cost him from 11s. to 15s. per acre, and with the scythe 8s., whilst with the machine it only cost him 5s. 9d., exclusive of wear and tear. From data supplied by a large number of their customers, Messrs. Samuelson & Co. make out that the saving by mechanical over hand labor is, as compared with reaping, 4s. per 1 acre, and with mowing, Is. 9d. per acre; and most farmers who have tried reaping-machines set down the saving at from 20 to 30 per cent. Besides, there is about a like economy in time, which is of immense importance in a variable climate like that of Great Britain.—See Woodcroft’s Appendix to Patents for Reaping-machines; Mr. Jacob Wilson’s ‘ Essay on Reaping-machines,’ in Transactions of Highland Society for January 1864; Book of Farm Implements, and Book of the Farm, by Henry Stephens; J. C. Morton’s Cyclopaedia of Agriculture.

PA’GING-MACHINE. Several machines have been inside for paging books and numbering banknotes, cheques, railway-tickets, and other similar papers. The great object of these machines is to prevent the chance of error or fraud by making it impossible that a page, cheque, &c. can be abstracted or lost without detection. Messrs. Waterlow and Sons of London perfected an ingenious machine, by which pages of books, such as ledgers and other commercial books, and banknotes, &c., are numbered in regular succession. The numbers are engraved on metal rowels, usually of steel or brass. A series of these rowels are so arranged, that when the machine is worked, the numbers must be impressed on the paper in regular succession from 1 to 99,999; and it is impossible to produce a duplicate number until the whole series has been printed. The instrument is made to supply ink to the types, so that it may be locked in such a manner as to admit of being worked without the chance of its being tampered with.

An extremely ingenious modification of this machine has been perfected by M. Auguste Trouillet of Paris, under the name of ‘ Numerateur Mecaniqua,’ which is not only more simple, but admits of wider application; for it not only pages books and numbers notes, tickets, &c., but can also be used for numbering bales and other packages of merchandise. The instrument has six rowels, on each of which is a set of engraved numbers, so arranged, that their revolutions produce in regular succession the required numbers, by the action of a lever which moves horizontally, and supplies the type with ink as it moves backwards and forwards.

PATENT LAWS. Since the introduction of the amended Patent Law in 1852 (see PATENTS), many manufacturers have boldly advocated the abolition of the patent system altogether; on the plea, that the good results, whatever they may be, are overbalanced by the bad. The great majority of advisers, however, call for further reform, not abolition. The Economic Section of the British Association has discussed this matter during a long series of years. The Society of Arts, also, have had many discussions on the subject; and the arguments pro and eon. will be found at length in the Transactions of these bodies. The various Chambers of Commerce throughout the kingdom have likewise debated the subject at length. The actual operation of the system may be briefly illustrated. Mr. Bennett Woodcroft, in 1864, examined 100 patents out of those which had been applied for in 1855. Of the 100, he found 96 frivolous in character, of little or no value as to the merit of the inventions; 4 of moderate value; and not one of striking promise. Out of the 100 applications, 70 patents were granted, of which one became void at the end of six months, 51 more at the end of three years, and 15 more at the end of seven years—because the patentees declined to pay the successive instalments of fees. There were therefore, in 1863, only 3 patents left out of the 100 which had been applied for in 1855. Mr. Woodcroft finds that about the same ratio is exhibited in the whole of the 3000 or so applied for every year. In 100 of the average applications in 1858, he pronounced that there was not one invention of much value, 3 of some, and 97 of little or no value. In 1862, he found 1 of much, 1 of some, and 98 of little or no value. As to statistics of actual numbers, see patent office, library and museum.

In 1862, a royal commission was appointed to consider the whole subject of the patent laws, and to suggest alterations which might be useful. The commission collected evidence in that and the two following years, and made its Report in 1864. Other commissions and committees have made later inquiries, and offered suggestions founded on the evidence collected; but the opinions expressed, on almost every point, are most conflicting. The divided opinion of practical men has hitherto discouraged any attempt to legislate on their recommendations; and the act of 1852 remains still in force.

PATENT is an exclusive right granted by the crown (in letters patent or open, whence the name) to an individual to manufacture and sell a chattel or article of commerce of his own invention. The policy of the present law of patents has latterly been much canvassed, and it has been suggested that, instead of the present monopoly, with the drawback of litigation to which it uniformly gives rise, the use of all inventions should be dedicated to the public at once, and the inventor rewarded by a pension from the state, according to the merits and utility of the invention. The present law allows the inventor to have a monopoly of his invention for fourteen years, with a further privilege at the end of that time, provided he has not been sufficiently remunerated, to have the patent renewed for a further term of fourteen years. That some mode of rewarding the individual whose perseverance and ingenuity have enabled him to discover a new invention should be established, is universally admitted, but whether it should be at the expense of that part of the public who are purchasers, and therefore benefited by his discovery, or by the public at large in the shape of a pension, is a matter still undecided. The evils of the present law are that there is a great deal of uncertainty in the mode of ascertaining what is a new invention. Hence, when a patent has been granted, if it is of such a nature as to lead to competition, infringements are almost matters of course, and the only mode of discovering and checking the infringement is so tedious, costly, and ineffective, that inventors generally pass their lives in constant litigation, fighting in detail a succession of imitators who often have nothing to lose by defeat, and therefore entail all the greater burden on the legitimate manufacturer.

It has been said that not more than three patents per cent. are remunerative. A royal commission has latterly been engaged in inquiries as to the best mode of remunerating inventors, and improving the law in reference to infringements; but it is doubtful how far the subject is capable of being put on a better footing, so many difficulties being inherent in it. The crown seems always to have enjoyed the prerogative right to grant monopolies, and this had been so greatly perverted in the time of Elizabeth, that the popular clamor led to a statute in the following reign, having for its object to prevent the crown in future making any grants of that kind which should be prejudicial to the interests of trade. By that act an exception was expressly made in favor of new inventions. At first the judges construed grants of monopoly to inventors very strictly; but afterwards it was seen that they were for the benefit of trade, and were dealt with more liberally. An important modification of the law was introduced by a statute of Queen Anne, which required every inventor to describe in detail the nature of the invention in an instrument called a specification. Another statute of 5 and 6 Will. IV. c. 83, further altered the law by allowing parties who had a difficulty in separating what was new from what was old in their invention to enter an express disclaimer of that part which was not new. But the most important alteration was made in 1852, by the statute of 15 and 16 Vict. c. 83, which reduced the fees, and otherwise improved the practice attending the obtaining of patents for the United Kingdom. Before stating shortly the substance of this act, it may be observed that there lias always been a difficulty in defining what is an invention that is patentable—a difficulty which no act of parliament can get rid of, for it is inherent in the subject-matter. It lias been held that a patent must be not merely a discovery of a new substance or article of food, but it must be a combination of processes producing some new result, or an old result by different means. It is of the essence of the patent that it be entirely new, that is, that it should not have been described in a published book, or well known in the business of the world, nor publicly used before. The specification must give a full disclosure of the secret, and describe it so that an intelligent person could from the description make the article itself.

There is a patent office in London, in Edinburgh, and in Dublin, but the Scotch and Irish offices have long been used only as places for inspecting copies of patents, specifications. and documents. From 1852 till the new Act of 1883 came into force, the commissioners of patents were the Lord Chancellor, Master of the Rolls, Attorney and Solicitor General of England and Ireland, and the Lord Advocate and Solicitor-General of Scotland. The inventor first presented a petition for a grant of letters-patent, accompanied by a statement in writing of the specification, a copy of which was left at the patent-office. The application was referred, as a matter of course, to one of the law officers of the crown, who might call to his aid a scientific person to be paid by the applicant. A provisional patent might be applied for in the first instance, and the complete patent deferred for six months— the patent dating from the first application. After a patent was granted, and had been in existence for three years, a fee of £50 fell to be paid; and, at the end of the seven years, a fee of £100. The letters-patent extend to the whole of the United Kingdom. The practice with reference to patents, especially as to the drawing of the specification, was too minute to justify an inventor to attempt to take out a patent without professional aid; and a class of persons called patent agents (a business for which no qualifications were required by any constituted authority) devoted themselves to this branch of business—their charges (often exorbitant) being generally ascertained by estimate beforehand. The fees payable to the law officers were as follows : On leaving petition for grant of letters-patent, £5; on notice of intention to proceed with application, £5; on warrant of law officer for letters-patent, £5; on sealing of letters-patent, £5; on filing specifications, £5; at or before expiration of third year, £50; at or before expiration of seventh year, £100. Besides these fees, if opposition was entered to the grant, additional fees were incurred, both by the party applying and the party opposing.

At the date of the passing of the Patents, Designs, and Trade Marks Act of 1883, there were nine acts on patents more or less fully in force; and six others on copyright of designs. Now the management of this branch of the public service is put under the Science and Art Department, and the new responsible official, called the Comptroller of "Patents, is an officer of the Board of Trade—from whose decisions, however, there is in certain cases an appeal to a court comprising some of the chief law officers of the crown. There is a paid examiner of patents, to whom applications are first submitted. Heretofore, seven different applications were necessary; now one suffices, and that may be sent through the post. The formulas are simplified, with the hope of enabling the patentee to dispense with the services of patent agents. In contrast with the scale of fees given above, the charges under the new law are : £1 paid down at once, when the provisional specification is lodged at the Patent Office; £3 more after nine months, when the final specification is passed by the Comptroller, and sealed; £50 after the fourth year ; and £100 after the ninth. The latter two payments may be made in annual instalments. (The Board of Trade has power hereafter to reduce the fees, on obtaining the consent of the Treasury.) A register of patents is to he kept, and an Illustrated Journal of Patents officially published. Patents, as formerly, hold for 14 years, and extend to the whole of the United Kingdom.

A patent obtained in this country does not extend to the colonies, but several of the colonies have machinery for granting patents for a like period. In the United States, patents are granted for a term of 17 years. In France, the term is 5, 10. or 15 years, at the option of the applicant; in Prussia, for 15 years; in Russia, for 3, 5, or 10 years; in Spain, for 5, 10, or 15 years; in Belgium, for 20 years; in Holland, for 5, 10, or 15 years; in Austria, not more than 15 years; in Sardinia, 15 years. In all cases, fees are exigible from the patentee. See patent laws and patent office.

THEO’DOLITE (Gr. theao, I see, dolichos, long), an instrument much employed in land-surveying for the measurement of angles horizontal and vertical, is neither more or less than an altitude and azimuth instrument, proportioned and constructed so as to be conveniently portable. Like all instruments in very general use. the variations in its construction are almost numberless; but its main characteristics continue unaltered in all forms. It consists essentially of two concentric circular plates of copper, brass, or other material (the upper plate, or upper horizontal, either being smaller, and let into the lower, or lower horizontal, or the rim of the lower raised round the outside of the upper), moving round a common axis, which, being double, admits of one plate moving independently of the other. Upon the upper horizontal rise two supports, bearing a cross bar, which is the axis of a vertical circle moving in a plane at right angles to the former. This latter circle either has a telescope fixed concentric with itself, or a semicircle is substituted for the circle, and the telescope is laid above, and parallel to its diameter. The circles, as their names denote, are employed in the measurement of horizontal and vertical angles. For these purposes, the outer of the horizontal circles is graduated, and the inner carries the index-point and the Verniers (q. v.); the vertical circle is also graduated, and the graduations are generally read off by an index-point and vernier firmly attached to the supports. The upper horizontal is furnished with two levels placed at right angles to each other for purposes of adjustment, and has a compass-box let into it at its center. The stand consists of a circular plate supported on three legs, and connected with the lower horizontal by means of a ball-and-socket joint; the horizontal adjustment of the instrument being effected by means of three or four (the latter number is the better) upright screws placed at equal distances between the plates.

The telescope is so fixed as to be reversible, and the adjustments are in great part similar to those of other telescopic instruments, but are too numerous and minute to be here detailed. Both horizontal plates being made, by means of the screws and levels, truly level, the telescope is pointed at one object, and the horizontal angles read off; it is then turned to another object and the readings-off from the graduated circle again performed; and by the difference of the readings, the angular horizontal deviation is given; and when vertical angles are required, the readings are taken from the vertical circle in a similar manner.

BLASTING. Before gunpowder was invented, the separation of masses of stone from their native rock could only be effected by means of the hammer and wedge, or by the still slower method of fire and water. In soft and stratified rock, wedges are still used for quarrying stones for building purposes; but in hard rock, or where regularity of fracture is no object, gunpowder is ordinarily employed. There are two kinds of B.�first, the small shot system; and second, that of large blasts or ‘mines.’

The small-shot system consists of boring holes into the rock, of from one to six inches in diameter, and of various depths, according to circumstances. In hard rock, this is done by a steel-pointed drill, struck by a hammer, and turned partly round after each blow, to make the hole cylindrical. The addition of a little water serves to preserve the temper of the boring tool, and makes the rock more easy to cut. In soft rock, whenever the hole is to be vertical, a ‘ jumper’ is used; this is a weighted drill, which acts, merely by its own weight, when let fall from about a foot in height. The powdered stone is removed at intervals by a ’scraper.’ The rate of progress varies, of course, with the hardness of the rock.

At Holyhead, the average work done by three men in hard: quartz rock, with 11/2 inch drills, is 14 inches in depth per hour; one man holding the drill, and two striking. After the hole is bored, it is cleaned out, and the powder poured down. A wad of dry turf or hay is put over the charge, and the rest of the hole ‘ tamped,’ or filled with broken stone, clay, or sand. The shot is fired by a length of Bickford’s patent fuse. When it is desirable to prevent the stones from flying about, when the shot is fired, a shield of boiler-plate, or of brushwood weighted, may be laid over the hole.

Small shots may be fired, even under water, by enclosing the charge in a tin case, with a tube of powder reaching to the surface; or in a canvas bag, well tarred, tied at the neck round a length of Bickford’s fuse, which burns under water. The charge is inserted in the drill-hole; and the weight of the superincumbent water acts as tamping.

In removing the wall between the old and new Shadwell basins of the London Docks, shots were fired under water within a few yards of vessels lying in the basin, by using moderate charges, and by keeping a raft of timber floating over the hole, as a shield to prevent anything flying upwards.

The voltaic battery has been used for firing shots, chiefly under water, since 1839, in which year it was employed at the wreck of the Royal George and at the Skerryvore Light-house.

When a large mass of rook has to be removed at once, or where a steady supply has to be daily furnished of irregularly broken stone, for breakwater or other purposes, recourse must be had to large blasts, or ‘mines.’ The greatest isolated example of this kind of blasting was the overthrow, in 1843, of the Rounddown cliff at Dover, by 18,500 lbs. of powder, in three separate charges, fired simultaneously by voltaic electricity. But by far the grandest system of B. by mines is to be seen at quarries for supplying stone to the Breakwater at Holyhead, where small shots having been found inadequate, large mines were introduced in 1850. These large blasts are of two kinds�’shafts’ sunk from the top of the rock; and ‘headings,’ or galleries driven in from the face.

The shaft-holes are 6 feet long by 4 feet wide, of various depths, according to the height of the rock, but seldom much exceeding 60 feet. The deal-box, with, the charge of powder, p, is placed in a chamber cut at one side of the shaft, so that the tamping may not be in the direct upward line of fire. The tamping consists of the stone and debris which have come out of the shaft; and the wires from the battery are protected from injury by being laid in a groove cut in a batten placed up one angle of the shaft.

It is evident that the same point, p, in the rock may be reached as well by a heading or gallery driven in from the face of the rock, as by a shaft from the top, and often by a shorter route. Headings are made 5 feet high by 3 feet 6 inches wide, and are driven, if possible, along a natural joint in the rock. The direction of the gallery is changed and sunk at parts, to prevent the tamping from being blown out. Four men can, on the average, drive 5 feet run of heading per week; but cannot sink above 3 or 4 feet of shaft, which has a greater sectional area, and is more inconvenient to work in.

The charge of powder may be divided and placed in two or more separate chambers, as p, and p; and� it is� better thus to spread a heavy charge over a length of face, than to have it in one spot, at a greater distance from the face than about 30 feet. The charges for these mines vary from 600 lbs. to 13,000, and even more, pounds of powder; and the produce is from 2 to 6 tons of stone to the pound of powder, according to the density of the rock and the position of the mine.

Besides the quarrying of stone, B. is used for military objects, or where total destruction is aimed at, and an excess of powder is little or no objection.

Of late years great improvements have been effected in the production and application of explosive agents other than gunpowder, which latter, until lately, may be said to have been exclusively used for the purpose of blasting. Nitroglycerine (q. v.) and gun cotton (q. v.) were discovered within two years of each other; but while gun cotton was immediately applied to industrial purposes, nitroglycerine was destined to remain a chemical curiosity for about 16 years.

Dynamite is a preparation of nitroglycerine and porous earth, in the form of a pasty mass, which, without materially impairing its explosive properties, has the effect of rendering it perfectly safe to handle.

One of the most celebrated applications of boring and blasting to modern engineering was the driving of the Mont Cenis tunnel. See tunnel.

BLAST FU’RNACE. Many costly experiments have been tried of late years in order to determine, along with other related questions, the best form of the blast furnace in which iron is smelted. Which is the most serviceable form is as yet a very much disputed point, but according to the published accounts, furnaces of the unusual height of 80 to 100 feet give, as a rule, the best results. There are two types of blast furnaces, irrespective of differences in their forms, as regards the way in which they are constructed. Some are built with thick walls, either entirely of brick or of brick and stone, hooped with iron, forming massive towers. Others, again, are formed of comparatively thin brick walls, and depend for their strength on an outer malleable iron casing, in which case they are called cupola furnaces. The furnace A, in fig. 1, article IRON, is an example of the former, and the annexed figure represents one of the latter kind.

The various parts of the furnace are distinguished as follow: A is the shaft or body, generally either in the form of a cone or cylinder, or somewhat barrel-shaped, in which ease, the portion marked B is not distinguishable from the shaft. B. is called the boshes, and is the part of the furnace which, from the high heat to which it is exposed, usually gives way first. H is the hearth, and C is the tunnel-head, which, however, is usually wanting, when the mouth is closed by a bell and cone to save the gases generated in the furnace. P is the charging platform, and Q,Q, the opening through which the ore, fuel, &c., are fed. These materials are brought to the platform by hoists, inclines, or level gangways, according to the situation of the furnace. Just below the boshes there are four or five openings in the circumference for the tuyeres t, and another for the arrangements required for tapping the furnace As respects the latter, a is called the tymp-arch, immediately below which is placed the tymp itself, consisting of a rectangular iron box containing water in a coiled pipe. The hearth is prolonged in the direction of the dam-plate d, and the space between it and the tymp is filled up with sand or clay, in which there is a channel for the escape of slag. In the damp-plate is placed the tapping-hole, i, through which the molten iron is run off. The pipe at p conveys the blast, produced by a powerful blowing-engine, and heated to between 600� and 1400� F. The B. F. may tee used with the Siemens Gas Furnace. See IRON and GLASS.

ARTIFI’CIAL LIMBS. With the exception of the celebrated’ artificial hand of the German knight, G�tz von Berlichingen* [* The iron hand of this knight, who has been immortalized by Goethe, it preserved at Jaxthausen, near Heilbronn, and a duplicate of it is in the Schloss Erbach, in the Odenwald. It is stated in Scott’s Harder Antiquities, vol. ii,p. 206, that the family of Clephane of Carslogie ‘have been in possession from time immemorial of a hand made in the exact representation of that of a man, curiously formed of steel,’ which was conferred by one of the kings of Scotland on a laird of Carslogie, who had lost his hand in the service of his country.�See Notes and Queries for July 17, 1867, p. 35.] �who flourished in the early part of the 16th c. (1513), and who was named The Iron-handed � which weighed 3 pounds, was so constructed as to grasp a sword or lance, and was invented by a mechanic of Nuremberg, our knowledge of artificial limbs dates from the time of Ambrose Pare whose (�nures de Chirurgie were published in 1575. The twelfth chapter of that volume, as translated by Thomas Johnson in 1605, shows ‘ by what means arms, legs, and hands may be made by art, and placed instead of the natural arms, legs, and hands that are cut off or lost.

The accompanying figures are copies of his drawing of ‘ an I made artificially of iron (fig. 1),’ and of ‘ the form of an arm made of iron verie artificially (fig. 2).’ He also gives a drawing of ‘a wooden leg made for a poor man’ (fig. 3), which is simply the common wooden leg with bucket receptacle still in use. No improvements worthy of record were made from the time of Abrose Pare to the beginning of the present century, when Baillif of Berlin constructed a hand which did not exceed a pound in weight, and in which the fingers, without the aid of the natural hand, not only exercised the movements of flexion and extension, but could be closed upon and retain light objects, such as a hat and even a pen. ‘Artificial hands,’ says Mr. Heather Bigg, ‘ are now constructed, by means of which a pin may be picked up from the ground, a glass raised to the lips, food carried to the mouth, and a sword drawn from its scabbard, and held with considerable firmness; while a combined arm and hand is fabricated, which is equal to the ordinary requirements of histrionic declamation.’�Orthopraxy, 1865, p. 157. The utility of an artificial arm depends much on the nature of the stump. A stump above the elbow is best suited for an arm when it gradually tapers to its lowest end, and terminates in a rounded surface. When an arm is removed at the shoulder-joint, and there is no stump, an artificial arm can still be fixed in its proper place by means of a corset. In amputation below the elbow joint, the best stump is one which includes about two-thirds of the fore-arm; while a stump formed by amputation at the wrist is very unsatisfactory. The simplest form of artificial arm intended to be attached to a stump terminating above the elbow, ‘ consists of a leathern sheath accurately fitted to the upper part of the stump. The lower end of the sheath is furnished with a wooden block and metal screw-plate, to which can be attached a fork for holding meat, a knife for cutting food, or a hook for carrying a weight.’�Op. cit. .p. 160. The arm should he so carried as to represent the position of the natural arm when at rest. It is retained in its position by shoulder and breast straps, and forms a light, useful, and inexpensive substitute for the lost member. More complicated, and therefore more expensive pieces of apparatus are made, in which motion is given to the fingers, a lateral action of the thumb is obtained, and the wrist-movements are partially imitated; and a degree of natural softness is given to the hand by a covering of gutta-percha and India-rubber. Such a hand, says Mr. Bigg, is often more symmetrical in aspect than the natural hand, but it possesses no efficient grasping power. Hence provision has to be made for attaching various instruments to its palm, such as special hooks, which can be removed at pleasure, for driving, shooting, &c.; apparatus for using the knife and the fork, for grasping the pen, &c.: indeed, the number and variety of instruments capable of being applied to an artificial hand are extremely great. Nothing has tended so much to the very highest development of artificial arms and hands, as an accident which happened more than a quarter of a century ago to the celebrated French tenor, M. Roger, who lost his right arm above the elbow.

It was necessary, for his future appearance on the stage, that he should have an artificial limb, which would serve the purposes of histrionic action, and permit him to grab a sword and draw it from its scabbard. Such a contrivance was invented in 1845 by Van Petersen, a Prussian mechanician, and the French Academy of Sciences commissioned MM. Gambey, Rayer, Valpeau, and Magendie to report upon it. For a history of the nature of the limb, the reader is referred to the report which appeared in the Comptes Rendus for that date, or to Mr. Bigg’s Orthopraxy, pp. 176�181. The apparatus, which weighs less than 18 ounces, was tested upon a soldier who had lost both arms. By its aid he was enabled to pick up a pen, take hold of a leaf of paper, &c.; and the old man’s joy during the experiment was so great, that the Academy presented him with a pair of these arms. Van Petersen’s conceptions have been extended and improved by Messr. Charriere, the celebrated surgical mechanics of Paris, aided by M. Huguier, the well-known surgeon. A very marvelous arm has also been almost simultaneously constructed by M. Bechard, which,’ by means of a single point of traction, placed in pronation, executes first the movement of supination, next in succession the extension of the fingers and abduction of the thumb: the hand is then wide open.’ -Bigg, op. cit. p. 190.

Artificial legs having fewer requirements to perform than artificial arms, are comparatively simple in structure. We borrow the description of our figure of the ordinary bucket leg in common use amongst the poorer classes from Mr. Bigg’s Orthopraxy. ‘ It consists of a hollow sheath or bucket, A. accurately conformed to the shape of the stump, and having�in lieu of the more symmetric proportions of the artificial leg�a ‘ pin,’ B, placed at its lower end to insure connection between it and the ground. This form of leg is strongly to be recommended when expense is an object, as it really fulfils all the conditions excepting external similitude embraced by a better piece of mechanism. It is likewise occasionally employed with benefit by those patients who, from lack of confidence, prefer learning the use of an artificial leg, by first practicing with the commonest substitute.’ As, when the body rests on a single leg, the center of gravity passes through the tuberosity of the ischium, it is essential that the bucket should be so made as to have its sole point of bearing against this part of the pelvis.

Of the more complicated forms of artificial leg three are especially popular. The first of these is of English origin, and owing to its having been adopted by the late Marquis of Anglesea, is known as the Anglesea leg. For a description of it, the reader is referred to Gray’s work on Artificial Limbs, one of the firm of Grays having been the constructor of the legs used by the marquis. This was for a long time the fashionable artificial leg. The second leg worthy of notice is that invented by an American named Palmer, and called the Palmer leg. From its lightness and the greater ease of walking with it, it has long superseded the Anglesea-leg in America. In the third of these legs, also invented in America, and known as Dr. Bly’s leg, the principal faults of the two other legs have been completely overcome. The advantages of this leg are thus summed up by Mr. Bigg, who has fully described and figured its mechanism: (1.) Adaptation to all amputations either above or below the knee. (2.) Rotation and lateral action of the ankle-joint. (3.) Power on the part of the patient to walk with ease on any surface, however irregular, as, owing to the motion of the ankle-joint, the sole of the foot readily accommodates itself to the unevenness of the ground, which is an advantage never before possessed by any artificial limb. (4.) The ankle-joint is rendered perfectly indestructible by ordinary wear, owing to its center being composed of a glass ball resting in a cup of vulcanite; thus it never gets out of repair, as the Anglesea leg but too frequently does, and the original cost is almost the only one the patient incurs. (5.) The action of the ankle-joint is created by five tendons, arranged in accordance with the position assigned to them in a natural leg. These tendons are capable of being rendered tight or loose in a few instants, so that the wearer of the leg has the power of adjusting with precision the exact degree of tension from which he finds the greatest comfort in walking, and also of giving the foot any position most pleasing to the eye. (6.) There is a self-acting spring in the knee-joint, urging the leg forward in walking, and imparting automatic motion, thus avoiding the least trouble to the patient, who finds the leg literally and not metaphorically walk by itself. (7.) The whole is covered by a beautiful flesh-colored enamel, thus avoiding the clumsy appearance of the wood, as is always found in an Anglesea leg, admitting of its being washed with soap and water like the human skin. (8). At the knee-joint there is a mechanical arrangement representing the crucial ligaments, and affording natural action to that articulation by which all shock to the stump in walking is avoided. This leg is patented, and as might be expected, is somewhat expensive.

In cases of arrested development of the lower limbs, short-legged persons may be made of the ordinary height by the use of two artificial feet placed twelve or more inches below the true feet, and attached to the legs by means of metallic rods, jointed at the knee and ankle.

Other parts not entitled to be called limbs, can also be replaced by mechanical art�such as the nose, lips, ears, palate, cheek, and eye. In the present advanced state of plastic surgery, deficiencies of the nose, lips, and palate can usually be remedied by an operation; cases, however, may occur where an artificial organ is required. Artificial ears are molded of silver, painted the natural color, and fixed in their place by a spring over the vertex of the head. Loss of an eye causes sad disfigurement; but the artificial eyes of Boissonneau (see his Renseigements G�n�raux sur les Yeux Artiftciels, leur Adoption et leur Usage), which have been shown in all the recent public exhibitions, completely throw all others in the shade, and cannot be detected without the closest inspection. For further details on all these subjects we must refer to Mr. Bigg’s volume, which is a complete encyclop�dia on these and allied topics.

FILTER, FILTRATION. When solid matter is suspended in a liquid in which it is insoluble, it may be separated by various means. Under the article FlNlNG, various methods of causing such suspended matter to collect together and sink to the bottom or float on the surface, and thereby clearing the liquid, are described. The process of filtration consists in passing the liquid through some porous substance, the interstices of which are too small to admit of the passage of the solid particles, the principle of the action being the same as that of a sieve; but as the particles of fluids are immeasurably small, the pores must be extremely minute.

One of the simplest forms of filter is that commonly used in chemical laboratories for separating precipitates, &c. A square or circular piece of blotting-paper is folded in four, the corner where the four folds meet is placed downwards in a funnel, and one side is partly opened, so that the paper forms a lining to the funnel. The liquid passes through the pores of the paper, and the solid matter rests upon it. The chief advantages of this filter are its simplicity, and the ease with which the solid matter be removed and examined.

A simple water-filter for domestic purposes is sometimes made by stuffing a piece of sponge in the bottom of a funnel or the hole of a flower-pot, and then placing above this a layer of pebbles, then a layer of coarse sand, and above this a layer of pounded charcoal three or four inches in depth. Another layer of pebbles should be placed above the charcoal, to prevent it from being stirred up when the water is poured in. It is obvious that such a filter will require occasional cleaning, as the suspended impurities are left behind on the charcoal, &c. This is best done by renewing the charcoal, &c., and taking out the sponge and washing it. By a small addition to this, a cottage-filter may be made, which, for practical use, is quite equal to the most expensive filters of corresponding size. It consists of two flower-pots, one above the other; the lower one is fitted with the sponge and filtering layers above described, and the upper one with a sponge only. The upper pot should be the largest, and if the lower one is strong, the upper one may stand in it, or a piece of wood with a hole to receive the upper pot may rest upon the rim of the lower one. The two pots thus arranged are placed upon a three-legged stool with a hole in it, through which the projecting part of the lower sponge passes, and the water drops into a jug placed below. The upper pot serves as a reservoir, and its sponge stops the coarser impurities, and thus the filtering layers of the lower one may be used for two or three years without being renewed, if the upper sponge be occasionally cleaned. Care must be taken to wedge the upper sponge tightly enough, to prevent the water passing from the upper pot more rapidly than it can filter through the lower one.

A great variety of filters are made on a similar principle to the above, but constructed of ornamental earthenware or porcelain vessels of suitable shape. It would occupy too much space to enter upon the merits of the filters of different makers, especially as there is really very little difference between them in point of efficiency, and nearly all the domestic filters that are offered for sale are well adapted for their required purpose. In purchasing a filter, the buyer must not be satisfied with merely seeing that the water which has passed through it is rendered perfectly transparent�this is so easily done by a new and clean filter�but he should see that the filter is so constructed as to admit of being readily cleansed, for the residual matter must lodge somewhere, and must be somehow removed.

When large quantities of water have to be filtered, this becomes a serious difficulty, and many ingenious modes of overcoming it have been devised. In most of these, water is made to ascend through the filtering medium, in order that the impurities collected on it may fall back into the impure water. Leloge’s ascending filter consists of four compartments, one above the other; the upper part, containing the impure water, is equal in capacity to the other three. This communicates by a tube with the lower one, which is of small height. The top of this is formed by a piece of porous filtering-stone, through which alone the water can pass into the third compartment, which is filled with charcoal, and covered with another plate of porous stone. The fourth compartment immediately above the third, receives the filtered water, which has been forced through the lower stone, the charcoal, and the upper stone. A tap is affixed to this, to draw off the filtered water, and a plug to the second or lower compartment, to remove the sediment.

In the diagram-showing this filter in section, the figures 1, 2, 3, and 4 indicate the corresponding compartments. At f, the top of the tube by which the first and second compartments communicate, a sponge may be placed to stop some of the grosser impurities.

Since 1831, when this filter was contrived, a number of ascending filters have been patented, many of them being merely trifling mollifications of this. Bird’s Siphon Filter is a cylindrical pewter vessel containing the filtering media, and to it is attached a long toil of flexible pewter pipe. When used, the cylinder is immersed in the water-butt or cistern; and the pipe uncoiled and bent over the edge of the cistern, and brought down considerably below the level of the water. It is then started by applying the mouth to the lower end, and sucking it till the water begins to flow, after which it continues to do so, and keeps up a large supply of clear water. This, of course, is an ascending filter, and the upward pressure is proportionate to the difference between the height of the water in the cistern and that of the lower end of the exit tube. See SIPHON. Sterling’s filtering tanks are slate cisterns divided into compartments, the water entering the first, then passing through a coarse filter to a second, and from there through a finer filter to the main receptacle, where the filtered water is stored and drawn off for use.

A common water-butt or cistern may be made to filter the water it receives by the following means : Divide the cistern or butt into two compartments, an upper and a lower, by means of a water-tight partition or false bottom; then take a wooden box or small barrel, and perforate it closely with holes; fit a tube into it, reaching to about the middle of the inside, and projecting outside a little distance; fill the box or barrel with powdered charcoal, tightly rammed, and cover it with a bag of felt: then fit the projecting part of the tube into the middle of the false bottom.

It is evident that the water can only pass from the upper to the lower compartment by going through the felt, the charcoal, and the tube, and thus, if the upper part receives the supply, and the water for use is drawn from the lower part, the whole will be filtered. It is easily cleaned by removing the felt and washing it.

Various means of compressing carbon, into solid porous masses have been patented, and filters are made in which the water passes through blocks of this compressed carbon. Most of these are well adapted for the purpose, but their asserted superiority over filters composed of layers of sand and charcoal is doubtful. A very elegant and convenient portable filter for soldiers, travelers, and others who may require to drink from turbid ponds and rivers, was constructed of Ransom’s filtering stone, and is also made of

the compressed carbon. A small cylinder of the stone or carbon is connected with a flexible India-rubber tube in such a manner that the cylinder may be immersed in a river, the mouth applied to a mouth-piece at the other end of the tube, and the water drawn through the filtering cylinder.

The filtration of water on a large scale will be treated of under WATER-SUPPLY.

Some very interesting experiments were made by Mr. H. M. Witt, to ascertain whether soluble matter, such as common salt, is in any degree removed from water by filtration. Theoretically, it has been assumed that this is impossible, since the filter only acts mechanically in stopping suspended particles; but the results of Mr. Witt’s experiments show that from five to fifteen per cent, of the soluble salts were separated by sand-filters such as above described. This is a curious and interesting subject, well worthy of further investigation. Another most important matter, on which a series of accurate experiments is required, is to ascertain to what extent soluble organic matter may be decomposed by filtration, especially by charcoal filters, and to ascertain how long charcoal and other porous matter retains its property of acting on organic, matter in watery solution. The power of dry charcoal in decomposing organic matter in a gaseous state is well established (see below), and it is also well known that fresh charcoal acts powerfully upon organic matter in solutions, but the extent to which this power is retained in the charcoal of a filter in continuous action has not been satisfactorily ascertained. This is of the highest importance, as it sometimes happens that water of brilliant transparency, and most pleasant to drink, on account of the carbonic acid it contains, is charged with such an amount of poisonous organic matter as to render its use as a daily beverage very dangerous. Charcoal obtained from burning bones is still more efficacious than charcoal from wood. A filter of animal charcoal will render London porter colorless. Loam and clay have similar properties. Professor Way found that putrid mine and sewer-water, when passed through clay, dropped from the filter colorless and inoffensive.

When a liquid contains mucilaginous or other matter having viscous properties, there is considerable difficulty in filtering it. as the pores of the medium become filled up and made water-tight. Special filters are therefore required for syrups, oils, &c. Such liquids as ale, beer, &c., would be exceedingly difficult to filter, and therefore they are clarified by the processes described under fining. Oil is usually passed through long bags made of twilled cotton cloth (Canton flannel). These are commonly 4 to 8 feet long, and 12 to 15 inches in diameter, and are enclosed in coarse canvas bags, 8 or 10 inches in diameter, and thus the inner filtering-bag is corrugated or creased, and a large surface in proportion to its size is thus presented. Syrups are filtered on a small scale by confectioners, &c., by passing them through conical flannel bags, and on a large scale in the creased tag -filter just described. Thick syrups have to be diluted or clarified with white of egg, to collect the sediment into masses, and then they may be filtered through a coarse cloth strainer. Vegetable juices generally require to be treated in this manner.

The simple laboratory filter has to be modified when strong acid or alkaline solutions, or substances which are decomposed by organic matter, require filtration. Pure silicious sand, a plug of asbestos, pounded glass, or clean charcoal, are used for this purpose. B�ttger recommends gun-cotton as a filter for such purposes. He has used it for concentrated nitric acid, fuming sulphuric acid, chromic acid, permanganate of potash, and concentrated solutions of potash and aqua regia. He says that properly prepared gun-cotton is only attacked at ordinary temperatures by acetic ether.

Filtering paper for laboratory purposes requires to be freed from inorganic impurities that are soluble in acids, &c.; this is effected by washing the paper with hydrochloric acid, or, when thick, with nitric and hydrochloric acid, and removing the acid by washing thoroughly with distilled water.

When a considerable quantity of liquid has to pass through a filter, it is sometimes desirable that it should be made to feed itself. In the laboratory, this is done by inverting a flask filled with the liquid over the filtering funnel, the mouth of the flask just touching the surface of the liquid when at the desired height in the funnel. As soon as it sinks below this, air enters the flask, and some liquid falls into the funnel. On a large scale, self-acting filters are fed by the common contrivance of a ball-cock and supply-pipe.

Air-Filters�The extraordinary powers of charcoal in disinfecting the gaseous products evolved from decomposing animal and vegetable matter, have been made available by Dr. Stenhouse in constructing an apparatus for purifying air that is made to pass through it. A suitable cage, containing charcoal in small fragments, is fitted to the opening from which the deleterious gases issue, and is found to render them perfectly inodorous, and probably innocuous. The first application of this was made in 1854, when a charcoal air-filter was fitted up in the justice-room of the Mansion House, London, the window of which opens above a large urinal, the smell of which was very offensive in the room.

The filter at once destroyed the nuisance, and the charcoal has ^Keen found to last many years without the need of renewal. 103 of such filters have been applied to the outlets of the sewers of one district of the city of London, and no bad smell is observable where they are placed, and no obstruction offered to the ventilation of the sewers. They have been applied with like results in two or three county towns. The subject is fully treated by Dr. Stenhouse in a letter to the lord mayor, published by Churchill (London). Charcoal respirators are small air-filters of the same kind applied to the mouth. See RESPIRATOR.