WATT'S JIB CRANE. It is not more trite than true, that many of the most valuable improvements in the arts, and more especially in practical mechanics, have been made by common workmen, who, from situation and circumstances, have been unable to reap the fair and proper reward of their genius; and who have lived in poverty, obscurity, and neglect, while the public were enjoying the benefit of their inventions, and sometimes while men of less talent but more worldly prudence and cunning, were laying claim to the inventions themselves; thus depriving the proper inventors both of their emolument and their honour. It must, indeed, be admitted, that the workman who has both the head to invent and the hand to execute, has not always that prudence which is necessary for insuring success in the world. Absorbed and occupied by his inventions, he has no time, and will not descend to calculate the result in pounds, shillings, and pence. Besides, a workman of superior abilities is always courted and caressed by his fellow-workmen: they need his advice and assistance; and the usual way of paying him for these, is by a treat in the ale-house. That which at first is only the receiving of a courtesy, becomes a habit through time; and the man is lost both to himself and to society.

To prevent this fatal, and, we fear, rather frequent result, would be a most desirable matter-although we are not prepared to say how it could be done; and, indeed, leaving this altogether out of the question, we know of no means by which a poor man can at present secure to himself the advantages of any invention, however important. The Patent Office was perhaps intended for the encouragement of inventive genius ; but, as at present managed, it does not answer that intention. The fee for all inventions, great and small, real and pretended, is nearly the same; and the amount of it is such as to preclude the application of any labouring mechanic. By this means, ninety-nine hundredth parts of the talent which would be at work

in the invention and improvement of machinery, is laid on the shelf; and the office which may have been meant for the encouragement of that talent, is haunted by quacks and impostors.

These observations have been forced upon us when we reflected upon the difficulty that we had in finding out the inventor of the very ingenious and useful crane which is the subject of this article: and all that we have been able to ascertain concerning him is, that his name was Francis Watt; that he was born at or near Aberdeen; that he worked as a journeyman carpenter at the bridge over the Spey at Fochabers, and at the Caledonian Canal; that he was for some time foreman of the carpenters at the construction of the Bell-Rock Lighthouse; that, while there, he invented this jib-crane, together with a very ingenious counterpoise one (of which we shall afterwards give a drawing and description), and gave a design for the temporary beacon which was set up up on the Bell-Rock; that, from the Bell-Rock, he came to England, in the service of Mr. Rennie, the engineer of that and many other great works; and that, after being for some time in the service of Mr. Rennie, he left it, and went we know not whither. It does not appear that Mr. Watt gave himself any trouble about those cranes, farther than furnishing the original idea and rough sketch from which they were constructed for the building of the Bell-Rock Lighthouse, the place where they were first used: and we are induced to lay them before our readers, both because they deserve to be better known, and lest some one to whom it does not belong, should arrogate to himself the merit of their invention.

The jib-crane possesses several advantages over the building cranes commonly in use; but these will be more easily understood after we have. described the several parts of the machine, as represented in the plate. The form and dimensions are taken from a crane which has been for several years used at the works carrying on at the Dundee Harbour; and although some alterations might

perhaps be made, we shall first describe the nature and uses of the crane, and then point out these alterations.

Explanation of the Plate.

Fig. 1 is a side view of the crane, showing the jib; fig. 2 is a back view, showing the chain, barrels, and edges of the wheels and pinions;" fig. 3 is a fulcrum, used in shifting the crane from place to place. The same reference-letters are put to the same points in both figures.

AB is the upright shaft. It is made of a firbalk 12 inches square, and 23 feet long. Its lower pivot turns in a cross step at A, and its upper one in a cross at B, supported by four gy-ropes, two of which (gg) are shown in each figure. Immediately above the pivot are two strong plates of cast-iron, bolted to the opposite sides, for receiving the bolt at D, upon which the jib turns. Above these, the shaft is fortified by side pieces, till it has a breadth of 26 inches, where are fastened the cast-iron cheeks (s s), of which an edge view is given in fig. 2, and which may be traced behind the wheels ii and n n, in fig. 1. Four brass beds, covered by cap squares of the same metal, are placed in these cheeks for receiving the axles of the wheels and pinions. Two strong cast-iron blocks, with grooved pulleys for the chains, are placed at c and r, upon opposite sides of the shaft.

CD is the jib, formed of two oak battens, 7 inches by 23 at their lower extremities, and 5 by 2 at their upper. They are 3 inches asunder at the lower extremity; where, and at the serpentine plate at the middle, they are separated by blocks, and they meet within a few feet of the upper extremity. The extremity D is fortified by two strong plates of cast-iron, which go withinside the plates in the shaft, and receive the axle-bolt; and other two plates at the extremity C, contain a grooved pulley, shown by the dotted circle at e and a bolt for fastening the chain Cr. The length of the jib from the axle-bolt at D to the centre of the pulley e, is 20 feet.

There are two chain-barrels. The barrel a raises or lowers the weight ƒ, by means of the chain which passes over the pulleys c, d, e; and the barrel o contracts or expands the jib, by means of the chain which passes over the pulley r. The crane-barrel (a) is about 9 inches in diameter, and the jib-barrel (o) about 8 inches; and the chains for both are made with circular links from five-eighths inch iron road. These barrels may be either both worked at the same time, in the same or in opposite directions, or either of them may be worked separately.

The jib-barrel has a single power, produced by the pinion p, of 10 leaves, and 5 inches diameter, acting on the wheel n n, of 76 teeth, and 36% inches diameter. The pinion p is moved by the winches qq, which have a lever power of 16 inches. The jibbarrel may be locked by pushing the moveable bolt v, till it bear against an arm of the wheel n n. The single power of the crane-barrel is obtained by placing winches (16 inch) on the squares k k (fig. 2), which terminate an arbor passing through the centre of the jib-barrel, and having on its one end the wheel ii, and on its other the pinion h (fig. 2). The pinion h (5 inches diameter, 9 leaves), moves the wheel bb, which is fastened on the arbor of the crane-barrel, and has 36 inches diameter, and 76 teeth.

The double power is obtained by turning the pinion by means of the winch m (16 inches), and one on the opposite end of the same arbor. The pinion is 8 inches diameter, and has 16 leaves, and the wheel ii, which it turns, is 32 inches diameter, and has 66 teeth.

The check-block d is a single pulley, kept in its place by the chains t, u, and is necessary for securing the action of the jib at all angles of elevation, by preserving the angle Ded, always smaller than the angle Def, it being obvious, from the doctrine of the resolution of forces, that when these angles are exactly equal, the point of the jib will be in equilibrio; but that when they are unequal, it will have a tendency to

move in the direction of the greater angle. When Def is the greater, the jib can be prevented from falling down by the jib-chain Cr; but if Ded were the greater, there is nothing to prevent it from rising till it would come in contact with A B.

The fulcrum (fig. 3) is, when the crane is to be shifted, placed near the axle-bolt of the jib at D; then the jib is lowered, and acts as a lever in taking the weight of the crane off the cross-foot. The cross-head of the fulcrum moves on a pivot in the tripod, and by means of it, and easing off two of the gy-ropes while the opposite ones are hauled in, the crane is moved along in an upright position.

'The total cost of such a crane is about £70; and the parts are so constructed, that it may be used for many years without requiring the smallest expense for repairs.

The power of the jib-barrel, without making allowance for friction, is about 26, when the winch is in an horizontal position; but as the resistance of the weight varies with every change in the elevation of the jib, it is not possible to calculate the power which would be necessary to move it with any given weight. The more that the jib is elevated, the less power is required. The single power of the crane-barrel, without making allowance for friction, is about 24), and the double power about 101. is not possible to determine the friction exactly, because it varies both with the weight and the position of the chains, being more as the weight is greater, and the angles formed by

It

Ithe chains less. But the result of experiments made with a load of one ton, and the jib at an angle of about 45 degrees, were as follows:

Hence the whole friction on the single power is equal to about twofifths, and that on the double power about one-half of the power employed; and the friction upon the checkblock nearly one-seventh of the power in both cases. The small arc, however, over which the winch can traverse, without a great alteration of power, when trial is made by weights suspended from the winch, and the great strain produced by a pressure of two tons on the machine, render such experiments but very loose approximations.*

The

As a building crane, this possesses many advantages over those commonly in use, from the complete command it has over every inch of space within the range of the jib. common building crane, with a fixed jib and moveable truck, commands, indeed, the same angular range; but, then the truck cannot, without an additional power, be removed farther from the shaft, after the crane is loaded, and thus its operation is confined. The common crane is also much less portable, and cannot be moved even for the shortest distance,

Still it is evident, that, could the checkblock be dispensed with, the power of the crane would be very much increased.. Now, if the point of the jib did not require to be very much raised, the block might be dispensed with by giving the pulley ca situation lower down the shaft, such as x; but if it were brought very low, the chain would not coil properly on the barrel. This might, however, be obviated, by placing the crane-barrel on the other side of the shaft, and bringing the chain down the back of the jib from the pulley e, without passing it over any other pulley what ever. As, however, the placing of the bar. rel in this situation, would prevent the jib from being brought so near to the shaft as it can be with the check-block; and as, notwithstanding the friction on the block, the crane is sufficiently powerful, the al teration is a matter of less importance.

without being taken down-an operation which costs a good deal of time and labour. Indeed, in as far as portability, power, and the complete command of a given space are concerned, this crane is decidedly superior to every other; and in every case of building with large stones, where gy-ropes can be used, it deserves the preference. Where gy-ropes cannot be used, Mr. Watt's balance, or counterpoise crane, is equally applicable and excellent. Indeed, the whole machines invented by this ingenious mechanic, while employed at the construction of the Bell-Rock LightHouse, form a series of applications of the mechanical powers highly unique and valuable; and show of how much consequence it would be to the arts and to society, were mechanical genius in common workmen duly appreciated and regarded.

New Menstruum for Etching Steel Plates, invented by Mr. EDMUND TUrrell, Engraver.

Take four parts, by measure, of the strongest pyroligneous acid, chemically called acetic acid; and one part of alcohol, or highly rectified spirits of wine; mix these together, and agitate them gently for about half a minute; then add one part of pure nitric acid; and when the whole are thoroughly mixed, it is fit to be poured upon the steel plate.

When the mixture is compounded in this proportion, very light tints will be sufficiently corroded in about one minute, or one minute and a half; and a considerable degree of colour will be produced in about a quarter of an hour. But the effect may be produced much quicker by the addition of more nitric cid; or it may be made to proceed slower, by omitting any convenient portion thereof.

When the mixture is poured off the plate, it should be instantly washed with a compound, made by adding one part of alcohol to four parts of water; and the stopping-varnish, laid upon any part that is sufficiently corroded, should be thoroughly dry before the biting is repeated. Care should be taken to keep the mixture out of reach of the sun, or any artificial heat; because its valuable properties for this purpose would thereby be changed. It will be necessary also to observe, that no more of the ingre

dients should be mixed than are wanted for present use, as the mixture will be greatly changed if kept many hours.

Care must be taken not to use the common Brunswick black, sold in stonebottles at the various oil-shops. This article is generally made by dissolving English asphaltum, prepared from coaltar, in the essential oil of turpentine, and digesting therewith a small quantity of spirits of wine, which, if properly managed, causes it to dry very quickly; and, on that account, it is found very convenient for stopping-out on copper-plates; but a little reflection will readily suggest, that this is a very improper compound to stop-out with, where alcohol forms one of the articles used to dilute the acid, as is the case in the compound given above. The stopping-varnish that answers the purpose best, is made by dissolving the best Egyptian asphaltum in the essential oil of turpentine, which dries sufficiently quick for all desirable purposes, and perfectly secures the part covered with it from the action of the menstruum. As a proof of this, I have used the varnish, so made, upon a steel plate etched by Mr. Bromley, jun., two feet eight inches long, by two feet wide; and, although the stopping-out was frequently repeated, yet it resisted the action of the acid to the last, the whole time of biting-in being about eighteen minutes.

On the Colour of Gold, and the Methods of Restoring it when Sullied. By the late WILLIAM LEWIS, M. D.*

The bright and deep yellow colour of gold, commonly distinguished by its name, is one of the most obvious characters of this metal. Its colour and beauty are of great durability, not being injured either by air or moisture, nor by any kind of exhalations that usually float in the atmosphere; as may be observed in the gildings of some public edifices, which have resisted the weather, and the vapours of London and other populous cities, for half a century, or more. In this property consists a great part of the excellence of this metal, for ortamental and some mechanical uses. There is no other malleable metallic body so little susceptible of tarnish or discoloration, or so little disposed to communicate any stain to the matters with which it lies in contact.

From his "Cemmercium Philosophico. Technicum."