chief items in making up prime costs, to which the remuneration of capital has to be added, to be considered presently.

4. Prime Cost.-Prime cost includes that of two great classes of work-orders and stock. In each of these are comprised wages, materials, cost of supervision, general charges, contingencies, and interest on capital.

With regard to orders and stock it is necessary to charge these in separate ledgers, to separate order numbers, and to transfer portions of stock to orders when wanted. Stock affords an economical method of production in quantity, lessening the prime cost per piece by comparison with the cost of single pieces, or of small numbers of pieces if done for their orders, so that the stock prices charged over, and the order prices, are taken in making up the prime cost of a job.

The cost of supervision is that of managers and foremen. Under general charges a great Ideal is included, both in materials and men. It may include clerks, gatekeepers, the amount drawn by the principals weekly from the firm, travelling expenses, agents, advertisements, rates and taxes, petty cash, besides some portions of materials for common use in every shop. Separate accounts are kept of all these in separate books, but the sums total can be added up at stated intervals, and an average obtained as a basis for general charges for a given period, say six months, or a year to come, to be divided pro rata on every order that goes through the works.

Contingencies are a charge on estimates, added to estimated prime cost. Interest on capital is also added, and this brings us to the question of capital sunk in a works.

5. Capital. In estimating capital, the following items have to be considered. The buildings, the plant, and machines, depreciation, losses, income tax, reserve funds, assets, which include buildings, plant, and machinery, and drawings, patterns, tools, stores in hand, patents, goodwill. It is easy to see how much of detail these matters open up, some of which will be found treated under their suitable headings. Capital charges become very complicated; so much so, that firms are often the best judges as to the amounts to be debited under the several headings here given. As far as the

present article is concerned, the point to emphasise is that every item must be taken separately, and kept as a separate account, and each must be made the subject of a rigid valuation at least once a year. A term of years is too long for a safe basis for these, so rapidly do conditions change at certain periods.

Depreciation is another general charge on capital, but one which is usually kept distinct, and properly apportioned in the work of certain shops alone. Thus for example, the greatest depreciation occurs in the shops where most machinery is used, and it is not fair to load, say, forgings or patterns with depreciation charges of lathes, planing, milling, and other machine tools. Great differences of opinion and practice exists in regard to the percentage of depreciation permissible. A much larger sum is now allowed than was the case a few

years ago. A large special reserve fund has to be set aside from each year's profit for this item.

6. Profit and Loss.-When all the foregoing are collated and balanced, then a true profit or loss account is obtainable. A good system of accounts is absolutely essential to this result, and one which distinguishes between the different shops. Foundry costs are quite distinct as far as labour and materials are concerned from those of the turnery and machine shop; thus each shop must be rated apart from every other. This is not always done.

The accounts of a large firm of engineers are therefore akin to a scientific analysis. A large amount of bookkeeping, and a big staff of clerks are essential. A far greater amount of attention is given to the subject now than formerly. It pays, because firms are able to detect weak points in their system of manufacture, and remedy them. It is most desirable that a firm should be able to ascertain its exact standing at any period, and this is only possible by the adoption of a very complete system of account keeping.

Accumulated Work.-By accumulated work is meant the work, power, or energy stored up in a body in virtue of its motion. An example is seen in a shell fired from a gun, for in piercing wood or armour plate it performs work, overcoming great resistance. A pile

The accumulated work in the rim of a flywheel is equivalent to that of a falling body of a corresponding mass and velocity. The mean diameter of the rim is usually taken as the radius of gyration, and the weight of the arms is neglected.

Accumulator, Electric. See Storage Battery.

Accumulator, Hydraulic.-This device is the equivalent of a natural head of water, and it affords an artificial means of producing a statical pressure similar to that of the natural head. The accumulator has the advantage over the head in the fact that the pressure is under control. It was an early invention of the late Lord Armstrong.

with any heavy materials at hand, as slag or stones; in the second, employed where space is limited, segmental rings of cast iron are carried on a bottom ring. Besides these, there are

Fig. 1.-Weight Case Accumulator, with Guides.

two bolts, which support the loading weights on the bottom plate. The inlet and outlet pipes are screwed into the bottom plug.

Accumulators are fitted with a safety valve, and when belt-driven pumps are used, with a deflecting valve also, to allow the water delivered to be returned to the suction tank when the accumulator is at the top, so relieving the pumps of the load. If worked in conjunction with steam-driven pumps, an automatic hydraulic stopping and starting gear is often provided to act upon the steam valve.

At 1,500 lb. pressure per square inch, each gallon pumped into an accumulator is nearly the equivalent of one actual horse-power.

Fig. 4 illustrates an intensifier or differential accumulator in section, by Messrs Henry Berry & Co., Ltd. It comprises two cylinders of different diameters set axially. The ram A in the large cylinder в acts as a cylinder to the smaller and fixed ram c, which is held in position by a crosshead and tension bars. The pressure is brought on the large ram A in the bottom cylinder, the ram is pushed upwards, and the water displaced by the fixed ram c. Pressure is thus intensified on the smaller one inversely as the difference in their diameters. Thus if the larger ram is 8 inches diameter and the smaller one 3 inches, these areas will be as 50.265 is to 9.424. If the pressure on the large ram is 700 lb. per square inch, that on the small one will be

9.424 50 265 :: 700: 3733 lb. per sq. in. Some intensifiers are made with removable weights for various pressures. Three-stage in tensifiers are also made.

The casting of the cylinders and rams of accumulators has to be done on end if a sound job is to be made. The usual working pressure of 1,500 lb. per square inch soon finds out spongy portions of these castings, and it is hardly possible, except by chance, to get sound castings poured horizontally, the top metal being more porous than the bottom. And if risers are put on, the metal is spongy in their vicinity. Casting perpendicularly not only avoids this, but ensures denser metal throughout. In the writer's experience, heads of from 4 to 6 feet in length have been also cast, so ensuring that the metal up to the top of the

actual casting shall be sound. This requires a deep casting pit, but it is essential. The pouring basin may, without inconvenience, be raised from 3 to 4 feet above the level of the foundry floor. Rams and cylinders are cast just as they stand when working, the stuffingbox end being uppermost. They are poured in dried sand.

A great difficulty in casting cylinders and rams is due to the cores. Chaplets are inadmissible, or at least very risky, because they produce some sponginess in their vicinity. The proper way is to sweep up the core on a very stiff bar, rigid enough to be self-supporting, and to carry it in a print impression of great length at the top end. Then, casting on end, the core is not likely to be washed out of centre to any appreciable amount. This applies only to cylinders and rams cast with blank ends. But when cylinders are cast with open ends, the lower one being bolted with an hydraulic joint to a base, prints can be fitted at both ends.

Rams must always be blank-ended. But a frequent practice is to core out the lower end simply to permit a print to be used there, to carry a thoroughfare core, making the hole less in diameter than that through the body of the ram, usually a 3-inch or 4-inch hole. Then it is bored and threaded, and a plug screwed in with rust cement.

In cases where a special order requires a cylinder and ram larger than the standard patterns furnish, expense can be saved by sweeping up a loam body to serve as a pattern, and making the flange for the stuffing box, and any other attachments in wood, and placing them in position on the loam body.

Acetylene Gas (sp. gr., 0.9).-Acetylene gas is remarkable alike for the simplicity of its generation, and for its high illuminating value. Although its production has long been a curiosity of chemistry, the commercial manufacture has been impossible, on the score of cost, until recent years. So long since as 1836 Professor Edmund Davy demonstrated the production of acetylene, although there was no prospect then of turning it to practical account. The cheap manufacture of calcium carbide (or carbide of calcium) has brought acetylene into extensive The carbide is produced by fusing coke

use.