twelve years old, the special surveys subsequently required will be Nos. 1, 2, and 3, at four, eight, and twelve years respectively from the date recorded in the Register Book of the previous special survey No. 3. In vessels classed "A" for special purposes, the above surveys must take place at three, six, and nine years respectively. If more convenient to owners, surveys are made in anticipation within twelve months of the dates at which they be come due. All repairs have to be inspected at the time when they are being carried out. Appeals from the surveyor's recommendations as to repairs can be made to the Committee. Provisional certificates are given in certain cases. Classes are liable to be reconsidered on surveys, and non-compliance with Rules involves the withdrawal of the class from a vessel. The A classification dates from the first Register Book of Lloyd's (1764). At that time the classification of hulls was denoted by the vowels A, E, I, O, and U, while letters G, M, and B referred to equipment. Thus AG denoted a first-class ship with a good equipment, while UB meant a poor ship with a bad outfit. In the next Register (1768) the numerals 1, 2, 3, 4 first appear, but the letters were small, al, b2, &c. The earliest Register in which Al appeared was that of 1775-76. At the date of writing, January 1905, the latest available returns gave the numbers of vessels classed thus:— At the close of the year ended 30th June 1904, 9,672 merchant vessels, registering nearly 173 million tons gross, held classes assigned by the Committee of Lloyd's Register. Further details are given in the table :- Abacus. See Calculating Machines. Abattoir. A modern abattoir in the large cities is of less importance as a place for the slaughter of animals than for cold storage. It includes refrigerating machinery, steam engines and boilers, and electric machinery, as well as workshops for the repairs and renewals that are always going on. The machinery of the actual slaughtering sheds consists chiefly of conveying tackle of the overhead type, travelling on joists or "runways," secured to hangers and to the walls, and of hoisting tackle worked from the walls. The city of Berlin has an immense municipal abattoir, in which, though the slaughtering is only done on one or two days in the week, the numbers killed include from 6,000 to 7,000 head of cattle, and from 20,000 to 25,000 pigs. In a building adjacent the engineering plant and storage chambers are contained. Here there are ten Lancashire boilers which supply steam to the engines and slaughter-houses. There are two compound tandem engines, each indicating 200 HP. and each driving two sulphurous acid compressors that being the medium employed for refrigeration. The four compressors are able to produce from 180 to 200 tons of refrigeration per day. geration per day. From these the sulphurous acid passes to three condensers containing copper coils, around which cold water is circulated by a pump, and agitated also by long blades on a vertical shaft. Thence the sulphurous acid passes to a refrigerator built of iron plates, and containing coils of copper pipes. The greater portion of this is for air cooling, but a small section is used for brine for pickling. The air supply is further cooled by passing it over trays by means of a fan running at 300 re volutions per minute. The brine falls in cascades through holes in the trays. The cooled air is then carried up shafts to the chill rooms above, which are served with overhead tracks for the handling of the meat. The doors are heat insulated with double thicknesses of wood, having sawdust between them. A separate system of air coolers supplies pickling cellars. The meat is not frozen, but kept just above freezing point. But a supply of ice is made for curing. An electric generating plant supplies light to the rooms, and power to the numerous hoists connecting the floors. The engines for this plant The engines for this plant are of 100 HP. and of condensing type, and there are two dynamos. The main building, exclusive of the slaughter-houses, is 500 feet long by 80 feet wide, and is four stories high. Abbreviations.—The practice of substituting short signs for full terms is one which is adopted in nearly all departments of engineers' work. Many of these are of merely local and limited significance, being applicable only to a firm's own practice, but large numbers are of general utility. Selections from these are given below. = = = Abbreviations used on Drawings, including the Drawing Registers.-Dr. Drawing; Tr. = Tracing; H. Sk. or Hd. Sk. Hand Sketch; Sk. Sketch; Bl. P. or B.P. = Blue Print; Br. P. = Brown Print; W.P. or Wt. P. = White Print. Revs. per Min. or Revs. per or R.P.M. Revolutions per Minute; H.P. or H. Press. - High Pressure; L.P. or L. Press. = Low Pressure; Int. = Intermediate; R.H. = Right Hand; L.H. = Left Hand. = = = = Metals and Alloys, Sections, &c.-C.I. = Cast Iron; W.I. or Wrot. I. or Wt. I. Wrought or Malleable Iron; M. or M.C.I. = Malleable Cast Iron; C.S. Cast Steel; M.S. Mild Steel; G.M. Gunmetal; C. Copper; B. Brass; Y.M. = Yellow Metal; P.B. = Phosphor Bronze; D.M. = Delta Metal; Al. = Aluminium; W.M. White Metal; R.H. Raw Hide; B.M. Babbitt Metal; L Iron Angle Iron; Steel L = Steel Angle; C = Channel Section; T = Tee Section; I = Joist Section; Sk. Pl. Sketch Plate. == == = = = = The sign is used in successive positions on a drawing between dimension lines indicated by crows-feet, to denote that all the successive Power, Temperature, Measurements, &c.-HP. = Horse Power; NHP. = Nominal Horse Power; IHP. = Indicated Horse Power; BHP. = Brake Horse Power; EHP. = Electrical Horse Power; Cent. or C. Centigrade; Fah. or F. = Fahrenheit; R. or Rea. or Reaum. Reaumur ; B.Th.U. = British Thermal Unit; G. Cal. Gramme Calories; Kg. Cal. Calories. In. or Inches; Ft. or 'Feet; Yd. = Yards; lb. = Pounds; G. org. = Gravity; G. or Gr. Gramme; Gal. Gallon; M. = Metres; mm. Millimetres; Cent. = Centimetres; KM. Kilometres; KG. Kilogrammes; MG. = Milligrammes; Dia. or Diam. = Diameter; Rad. Radius; Cir. or Circ. = Circumference; Lin. Linear; Deg. or = Degrees; = Relation of Circumference to Diameter, 3.14159; μ = Coefficient of Friction; = Angular Velocity; E = Modulus of Elasticity; I = Moment of Inertia; Z= Modulus of Section. = 100 = Meg. 1,000,000 Units; Myria = 10,000 Units; S = = = = brasses and their alloys, or white metals, and a sweet action is thus ensured. For portions, however, which only move or slide over each other slowly, two steel faces may be employed without trouble. In this class of fitting, hardening or case-hardening has very extensive use; surfaces would be rubbed away much too rapidly if it were not done, and would need frequent adjustment or renewal to keep the working parts up to action. This is especially the case with the smaller portions of mechanism, notably on machine tools, which have to endure very See also Algebraical Signs, Arithmetical hard service-dogs and catches for example. Signs. Abele. See Poplar. Abrasion.--Abrasion, or the wear of machinery parts, due to their rubbing together, has to be taken into account by engineers in many and various ways. (This is a distinct thing from Abrasive Processes.) The principal factor to be considered is how to counteract the effects of abrasion, or to delay its occurrence as much as possible. The natural effect of excessive abrasion is rapid working loose of parts, and this is an evil which cannot be tolerated in the majority of machinery. The better the class of mechanism, the more perfect will be the arrangements introduced for dealing with it. Two methods are--providing hard qualities of metal, so that the effects of friction are more slowly felt; and having means for taking up wear, or effecting renewals of vital parts as they become reduced or spoilt by abrasion. The firstnamed precaution is a most obvious one. comprises the use of hard cast iron, the substitution of cast steel for iron, the hardening of the portions which are most liable to be abraded, and the employment of separate pieces of harder metal, such as tips or shoes of cast steel, attached to the softer portions of mechanism not subject to friction. At the same time it must be noted that two hard substances will not run well together, so that abrasion may be actually induced if, for instance, a steel shaft is run in a steel bearing. The result is (unless very excellent surfaces are made, and abundant lubrication provided) that one face abrades and tears up the other, causing what is called Seizing. This is obviated by the employment of a softer metal for the bearing, as cast iron, or any of the It Increase of area of wearing surfaces is also a method of delaying the effects of abrasion, by spreading its action over a larger amount of metal. In the majority of cases where the presence of slackness cannot be permitted, the device of fitting adjustable parts is followed in addition to the provision just noted for delaying wear. This is done in practically all machinery, but is specially important on engines, and on machine tools of all kinds. In the first example, slackness produces knocking, with its evils; and in the second, accurate work cannot be done on a machine which lacks true guidance in its parts, By the employment of loose or adjustable pieces, close contact may be maintained between surfaces constantly. This aspect of the question will be found treated under Adjustments, Adjusting Screws, Adjusting Strips. Lubrication is a means of minimising the effects of abrasion, not only to prevent or hinder wear, but also to enable easy running to be secured. Without lubrication, it is impossible to revolve shafts, and move sliding surfaces under heavy service, or at high speeds. But with a suitable oiling or greasing medium successful running is attained, the lubricant forming an interposing film between the surfaces which work together, and so lessening or preventing their abrasive action upon each other. See Bearing Area, Lubrication, &c. Abrasive Materials.-The materials employed for abrasive processes are many, and varied in composition and quality, ranging from common sand to diamond dust. They comprise sand, grindstones, emery, corundum, carbo rundum, rouge, crocus, tripoli, putty powder, crushed steel, diamond dust or bort, oilstone. The great variations in the hardness and degree of finish necessary in work are sufficient to account for so many different kinds of substances being in use. Although several sorts of abrasives may be employed indifferently for certain work, there are instances where but one composition is adapted to a particular operation. Varying grades of the same material are also essential for different purposes, or for roughing and finishing processes, this being a question of coarseness or fineness of the abrading agent. The great demand for abrasives has resulted in increased supplies, and in the development and production of new materials, as well as in improvements in the applications of the existing varieties. Machinery for their employment has also been immensely developed, and the forms in which abrasives are shaped specially for use in these machines are innumerable. Abrasives take either what we may term natural forms, i.e., powders, or blocks, or they are made up into artificial shapes, to suit the purpose of their application to the work. In the former case, of which sand and natural grindstones are typical examples, the powder is used in either its loose dry state, or in a paste with liquids, and the solid stone is used in the form of blocks, or it is shaped into discs and rotated on an axle. These two instances were the first ones of the application of abrasives, but they have since been considerably affected, and in some cases ousted by other materials formed into special shapes for particular work, of which emery is the principal example. The primitive method of abrading-using a loose powder-is practised to a large extent, and all abrasives are brought into use by this mode of working. The substances depend for their successful action upon the constant changing of position which they undergo, being rolled or rubbed about incessantly, so that fresh abrading points are exposed. There is a limit to the abrading capacity, however, of the materials, so that after a certain amount of work has been done, they begin to lose their efficiency and get dull. This is noticed in such operations as glass grinding, where sand is employed between the glass and a rubber or disc of iron; the sand has to be constantly replenished, as the used grains begin to dull and cease effective action. In this particular respect abrasives vary widely, since some kinds. will do much more work than others; emery, corundum, and carborundum, for instance, are superior to sand in their endurance. is The grading of the powders for this form of abrasion produces a wide range of coarse and fine qualities suited to all classes of work. The varying grades of emery are an example of this, ranging from "corn" to "flour" sizes. For those finishes which the finest flour emery not delicate enough to produce, other materials are employed-rouge, crocus, &c. ; though these are not of so much value in engineers' work as in that of gold and silver-smiths, and various fine metal trades. The choice of an abrasive material cannot always depend upon its rapid action, since a very free and fast working material may produce too much scratching to be desirable, and therefore a more slowly operating substance must be chosen, even at the expense of time. Here, however, the value of grading comes in, since a surface can be roughed down with a rapidly working abrasive, and then finished with a smoother quality of the same or of another material. The hardness or softness also of an abrasive have much to do with the surface produced, apart from the fineness of grain. A very hard material may produce scratches, though it is finely divided, while a coarser grade of another substance may work satisfactorily. The advent of the practice of forming abrasives into solid shapes or attaching them to the surfaces of moving bodies has resulted in a considerable extension of the use of abrasive materials. In the form of wheels, of which emery discs, and cylinders are typical, they perform all kinds of intricate operations, and other plainer ones with rapidity and accuracy. This is due directly to the device of artificially shaping the wheels into forms suitable for the application of the abrasive to the work, frequently to enable processes to be performed which could not be done at all with loose powders or pastes. The production of an efficient bond or cementing material has enabled manufacturers to mould emery and other substances into in numerable shapes, some of them of delicate outlines, in which a natural grindstone would be too fragile. It is also possible to make wheels in numerous grades suited to the particular requirements of various metals and finishes necessary. See Grinding Wheels. The action of an artificial wheel while at work bears similarities to that of a powder in motion between surfaces-the particles of emery abrading the work being loosened and detached, so exposing fresh grains to operate. In the case of a revolving wheel these particles become scattered, instead of remaining between the wheel and work, so that a really more efficient and cleaner cut is attained. The loss of grains must not, however, be rapid, or the wheel will become worn away too quickly. On the other hand, retention of the particles for too long a period results in non-efficiency, because the front surface becoming dulled, ceases to operate, and the fresh grains below not being exposed, are able to do nothing. The happy mean in abrasion must therefore be struck to get the best results out of wheels, and special grades used for special work, and for different metals, hard, and soft. "Glazing," which occurs when a wheel is run too slowly, means the filling up of the pores of the wheel with the metal being ground, choking the action and stopping further abrasion from taking place. Many of the finer grades of abrasives, chiefly for polishing, are employed when spread over revolving bobs or wheels of wood, covered with leather, &c., and on travelling belts, by which awkward shapes are tackled. All these various aspects of abrasive materials will be fully discussed under the respective headings of the substances; and their composition, manufacture, and specific uses will be described together with the machines in which they are employed. Reference may also be made to the general remarks on Abrasive Processes. Abrasive Processes.--The property which certain substances possess of abrading or rubbing away softer materials is turned to valuable account in engineering, and other trades. Both the very roughest and the very finest classes of mechanical operations are alike effected by abrasion, from the fettling of castings to the finishing of high-class gauges, and lens-grinding, and polishing, work done to extremely minute fractions of the inch. The process of abrasion has peculiarities which are not possessed by true cutting tools. The extreme hardness of the abrading agent is the principal factor which enables many abrading operations to be performed, work which could not be done at all in some instances with steel cutting tools. This applies to all hardened steel pieces, and to tempered tools which can only be reduced or sharpened by abrasion. Their degree of hardness is of little account, since there is no hardened steel which cannot be easily attacked by the various abrading materials in use. The sharpening of cutting tools was obviously one of the first human applications of abrasion, and it still constitutes the most important operation. But another function which has immensely grown during recent years is the practice of finishing pieces of work either roughly or to the most precise dimensions at present attainable. The development of this class of abrasion or grinding has opened up a new field in mechanical operations, especially in connection with hardened pieces. The advantages of hardening wearing parts have always been apparent, but the distortion which follows the hardening process imposes limits to the extent of the operation, unless some means of rectifying the effects of such distortion is available. With the advent of emery and other wheels, the truing up of hardened pieces has become a comparatively simple job, and the effect upon engineers' and other work has been far reaching. But the most remarkable feature of the process of abrasion lies in the minute amounts of material which can be removed at a time. The case differs essentially from that of cutting tools. These must penetrate a surface to an appreciable extent before they will cut, so that very fine amounts of material cannot be taken off (except by a scraping action, which is another thing). The very finest results in finishing are therefore found to be effected by abrasion. The faintest contact, with friction of the abrading agent and the work, suffices to produce some amount of reduction, however small. What this means is that any number of separate rubbings or grindings can be made |