much as the screw surface is not placed at right angles, but obliquely to the direction of motion; and as the effect of power on speed is as the cube root of that power, it will be perceived that the drag of the screw, or the retardation of the vessel's speed by it, must be very little indeed, probably in the majority of cases not sensible to the log. In confirmation of this result, I find in Bourne's Treatise on the Screw Propeller, page 142, where the conclusions of the French experimenters on the screw vessel Pelican are cited, the following recommendations, viz: "but in the case of merchant vessels with auxiliary power, they recommend that the screw shall be made merely capable of revolving freely when disengaged from the engine, in the manner of a patent log. A screw thus fitted, will, they say, offer scarcely any obstruction to the progress of the vessel under sail, while it will possess advantages in strength and simplicity, such as would not be otherwise attained." In the last and most perfect screw vessels of the French Navy, as the Napoleon for instance, a screw of four blades is used, incapable of being hoisted out, as in the British Navy, where two bladed screws are wholly used; this number of blades being imperative where the screw is to be hoisted out. In the Napoleon the screw is simply uncoupled as in the Princeton, when it is desired to navigate the vessel with sails alone.

In addition to the mere drag of the screw just stated, there is a further retardation of the vessel's speed due to what is usually termed the screw's friction on the water; this is probably greater than the former. In the absence of all exact experiment, it is impossible to determine the value of these retardations, but I am persuaded it does not exceed one-tenth the vessel's speed; that is to say, a vessel which, disencumbered from the

would make 10 knots under sail, would make 9 knots dragging it. In the following tables of the performance of the Princeton, there will frequently be found what is called the negative slip of the screw. This, however, only occurs when the vessel is under sail and steam; it never occurs under steam alone. When it has place it is indicated by the minus (—) sign prefixed. By negative slip of the screw is meant the excess of the vessel's speed over the forward speed of the screw (revolutions multiplied by pitch) in per centums of the latter. Under these circumstances it might be supposed the screw, so far from assisting, was retarding the vessel's speed. Such, however, is not the case, owing to the facts of the screw being located at the stern, and the generation of a following current of considerable velocity by the advance of the vessel; this current flowing in behind the stern, supplies chiefly the water on which the screw acts, and it may be slipping considerably in this water and yet apparently have less speed than the vessel.

Boilers. The Princeton had two sets of iron boilers. The first set was designed by Ericsson; the second set by Chas. H. Haswell, at the time Engineer in Chief U. S. N. Both sets corroded out very rapidly. The first set underwent very extensive repairs in Dec. 1846, 2 years and 10 months after they were built, and they were taken out in April, 1847, 3 years and 7 months after they were built, so completely corroded out as to be impossible of repair. The last set on their return to the United States after two years' service were found to be greatly corroded.

The corrosion of the first set of boilers was greatest on the semi-circular

top of the shell above the water line, though the whole water surface was severely acted on. The top of the shell was not acted on in particular places, nor did the metal present honeycombed or pitted appearance, but the wasting seemed uniform over the whole extent. The reason was at the time a subject of general speculation, but none of the causes offered met the case. After the breaking up of the vessel, and the removal of the machinery, I had occasion to minutely examine the latter, and I found the brass feed pump of the port engine, its valves, valve seats, and valve chests, also of brass, in a completely corroded condition; the whole surface being honeycombed or pitted very thickly and very deeply, extending in many places nearly through the ths inch thick metal. On examining the corresponding feed pump of the starboard engine, made of the same material, similarly situated and performing the same office, I was surprised to find it in excellent order, with no marks of corrosion. At first I was at a loss to account for this difference, but upon reflection, recollected the Princeton's engines had no independent bilge pump, and that when under way the bilge water, which made very fast, (owing to a steady stream being admitted through the pipe surrounding the propeller shaft where it passed through the dead wood of the vessel, for the purpose of keeping cool and lubricating the stern bearing of the same shaft,) was taken out of the ship by a bilge injection, communicating with only the port engine, air pumps, and reservoir; the starboard engine having no bilge injection. Of course, the water fed to the boilers by the port engine pump, and the pump of each engine fed to all three boilers, was greatly mixed with bilge water, composed of sea water strongly impregnated with the acids and soluble matters of the green white oak of which the chief part of the vessel was made; and as these acids appeared to have had sufficient strength to attack and destroy the brass of the pump, it is highly probable they were also the cause of the far more rapid destruction of the iron of the boilers. In connexion with the foregoing I will also state, that no scale was made upon the fire surface of the boilers during the year I was attached to the vessel in the capacity of engineer, while steaming in the Gulf of Mexico, although the water in the boilers was never carried at less than twice the natural concentration, and frequently for days at two and a-half times the natural concentration, the steam pressure ranging from 10 to 12 lbs. per square inch. Although every part of the fire surface of the first boilers could be reached, and the scale jarred off had there been any there, yet there never was found enough to make the operation of scaling necessary. The U. S. steamship Mississippi, steaming at the same time in the same waters with copper boilers, made scale to a very inconvenient extent, with the water in the boilers carried at only one and three-quarters the natural concentration, with about the same pressure of steam. The Mississippi made scarcely any water, was built of seasoned live oak, and had independent bilge pumps. I ascribe the remarkable cleanness of the Princeton's boilers to the dissolving of the scale by the acid of the bilge water, and also to the continual falling off of the scale by the continual removal of impalpably thin layers of the iron by the action of these acids. In the engine room of the Princeton, the stench from the bilge water was overpowering.

VOL. XXVI.—THIRD SERIES.-No. 1.—JULY, 1853.

5

Both sets of boilers were utterly inadequate to supply the engines with the steam of proper pressure they could work off, cutting off at d the stroke from the commencement. By proper pressure, I mean 20 pounds in the boilers per square inch with wide throttles. The most violent forcing with the fan blast could not effect a reasonable approach to this; nor could there be maintained, for 24 or 36 consecutive hours, by any practicable amount of forcing the fires with the blast, over 10 pounds of steam, with the throttle half open, and cutting off at d. Much smaller engines could have worked off all the steam the boilers could supply, and of course could have developed the same power.

In calculating the evaporation of the boilers, I have confined myself to the steaming done after Commodore Stockton resigned the command, both because the data was sufficiently large, and because for that time only were the steam logs complete in all the elements; also, because the selection of the fuel was made with greater care while the vessel was making experimental trials. In calculating evaporation, Regnault's data for the latent heats of steam is used. In order to burn from 1200 to 1400 pounds of coal in either set of boilers, the steam pistons of the blowing engines were required to make about 30 double strokes per minute. These engines were two in number, with cylinders of 12 inches diameter, and 14 inches stroke of piston, the exhaust communicating with the condensers of the large engines. Worked by each blowing engine was a centrifugal blower of 4 feet diameter, composed of six fans 22 inches long by 12 inches deep; the blower was geared up with a belt, to make six revolutions for each double stroke of the steam pistons, the average being 180 revolutions per minute. With wide throttles, the pistons of the blowing engines would make 200 double strokes per minute. These engines were much larger than was required or could be used. The natural draft of both sets of boilers was very defective; the utmost of anthracite that could be burned with it was 6 pounds per hour per square foot of grate surface, or about 800 pounds per hour.

The economical evaporation of these boilers was only up to the ordinary standard. There was in both much too little heating surface for the fuel consumed, and the heated gases, especially with the first boilers, were delivered into the smoke chimney at a very high temperature. I have witnessed on a dark night, when using soft anthracite, and forcing the blowers strongly, a mass of dense red flame driven out from the top of the chimney, of its full diameter, and rapidly. On one occasion when forcing the vessel, this mass of red flame was of sufficient volume to stream over the taffrail, and brightly light up the decks around, alarming the officers of the ship, and requiring the cessation of the blowers.

The last boilers were superior in type to the first. They contain a considerably greater amount of heating surface in the same sized shells, and gave much higher economical results; but they were inaccessible for cleaning or repairs, while every part of the first boilers could be reached.

FIRST BOILERS.-Three iron boilers, with one tier of deep return flues. The boilers are placed side by side, with one smoke chimney in common.

Length of each boiler,

26 feet.

Weight of sea water in the three boilers, (12 inches above top

of flues, weighed,) 76,160 pounds.

of the three boilers, &c., complete, PROPORTIONS.-Proportion of heating to grate surface,

128,128 66

18.060 to 1.000.

Proportion of grate surface to aggregate cross area of the direct flues, 4.941

66

66

66
66

66

to cross area of smoke chimney, Square feet of heating surface per cubic foot of space displacement

Cubic ft. of steam room per cubic ft. of steam used per stroke of piston, 24-050 LAST BOILERS.-Three iron boilers, with double return, drop, circular flues. The boilers are placed side by side, with one smoke chimney in common.

Aggregate cross area of the upper row of flues in the three boilers, 18-363"

steam pipes, &c., Weight of sea water in the three boilers, (calculated,)

PROPORTIONS.-Proportion of heating to grate surface,

9 " 4 inches. 3000 square feet. 136

66

Proportion of grate surface to aggregate surface of upper row of flues, 7.046

Square feet of heating surface per cubic foot of space displacement

Cubic ft. of steam room per cubic ft. of steam used per stroke of piston, 18.990

(To be Continued.)

Stenson and Co.'s Patent Welding Hammer.

Compact soundness and homogeneity in wrought iron, are desiderata which practical men connected with engineering and smith work in general, have long sought after. But iron being subjected, during forging, to every variety of torsion, punching, and other tests, in the multiform uses to which it is made subservient, any defect occurring by cleavage or splitting while in the hands of the workman, is a direct loss both in time and material. Every improvement, therefore, in the welding, and greater uniformity in the character of the iron, cannot fail of being highly appreciated.

• From the London Mechanic's Magazine, March, 1853.

When bars made from "piled" iron, imperfectly welded, are used as piston or other rods, working through stuffing-boxes, longitudinal seams or lines of cleavage are frequently apparant throughout their length. The edges of these dark lines are usually rough and serrated, and are the too frequent causes of premature destruction to the hempen packings through which they work.

Defects in the welding of piled iron are also frequently manifest in the cleavage and lamination of the tyres on carriage wheels. It is no uncommon thing to see the tyre of a coach-wheel, after having only been a short time at work, and when but one-fourth or one-sixth worn, split and divide like the leaves of a book-a defect which at once renders its replacement indispensable. A compact iron was formerly produced in the "Catalan forge," or "Bloomery fire;" the fuel used being charcoal, which was supplied from the extensive woods then abounding in many parts of England.

By means of this private process, iron was made directly from the ore, and brought out of the fire in a solid mass, which, by being repeatedly heated and hammered, was ultimately reduced to the size and form required. But as those ancient woods became exhausted, the iron manufacture gradually retired from its former localities, and took its position chiefly in those districts where the coal-fields offered a cheap and abundant supply of fuel. The iron made by coke, however, though produced at a cost greatly below that of the charcoal forges, was found to be of a quality so inferior to that of the latter as to render improvement not only desirable, but indispensable to a successful competition and an abundant production.

The conversion of pig into malleable iron, by the process of "puddling," as invented by Cort, was an important step towards the desired end; but the iron thus made was found to be of a weak nature, known by the term "cold-short," more especially when the pig had been produced from ores containing an excess of silicon, phosphorus, sulphuret of iron, or other foreign matters.

With a view to the production of a more fibrous character in the iron, came next the "doubling and welding," or "rolling" the puddled balls, after they had been hammered, into "rough bars" or "puddled bars"a method now so generally adopted in our iron works. These puddled bars, being cut to the required lengths, are placed one upon another, and formed into "piles," which may be composed of from two or three to eight or ten plates. The furnace is now charged with as many of these piles as may be convenient, and when they are at a high welding heat the drawing and rolling of the charge commences.

The object effected by means of the patent process is a more perfect welding of the pile into a solid mass than has hitherto been accomplished; this preventing cleavage or lamination either in forging or in wear.

The usual method is to take the pile out of the furnace and draw it to a considerable distance along the floor to the rolls. During this time, the air acting upon and between the plates composing the pile, produces an oxidation and a cooling of the iron, which renders the welding imperfect. But by the patent process the welding is effected at the instant the pile