ON THE CHEMICAL CHANGE PRODUCED BY SOLAR RAYS. BY MR. ROBERT HUNT. [Being the substance of a communication to the Royal Cornwall Polytechnic Society.] After drawing attention to the very extensive and curious discoveries, which had been made during the past years, in the chemistry of solar radiations; the author proceeded to show, that these effects were not confined to the ordinary photographic preparations, but that they extended over a large series of the chemical compounds. In the first place, he drew attention to the accelerating influence of the sun's rays on precipitation. It was found that the sulphate of iron being dissolved in water containing a little carbonic acid, precipitated a considerable portion of the carbonate of iron, when it was exposed to sunshine; but that in the same time a similar solution in the dark gave no evidences of precipitation. An effect similar to this had been observed by Sir John Herschel, on a solution of lime and platinum, from which an insoluble platinate of lime was formed in the sunshine, but not any in the dark. A mixture of the iodide of potassium and the ferro-prussiate of potash, being exposed to good sunshine for a few hours, a decomposition was effected, and a considerable quantity of prussian blue was precipitated; in the dark the same mixture underwent no such changes. Several other similar cases were named, which Mr. Hunt intends still further to investigate. The effect of light on the colour of precipitates was next mentioned. It has long been observed by the French manufacturers of carmine, that that very beautiful preparation was procured of a much richer colour, if it was prepared in the bright sunshine, than if prepared in the dark, or on a gloomy day. Mr. Hunt had discovered that the chromates of silver and mercury as well as prussian blue, varied very much in colour, if they had been exposed during their preparation to the influence of the sun's rays, or otherwise. A still more remarkable effect had been observed by the author, which appeared to indicate some absorption of the principle upon which these changes depend. It is well known to chemists, that a solution of sulphate of iron will precipitate gold and silver in a metallic state from their solutions. In the dark this process occupies many hours-and even in diffused daylight a considerable time. If, however, either of the solutions-either the iron, or the silver, or gold-be exposed to solar influence for some time, they undergo a change by which the precipitation of the metal is immediately effected, even in the dark. It is not necessary that both solutions should be exposed; the iron solution alone is quite sufficient. May we not then suppose that the principle producing these curious chemical changes, is absorbed by the fluid during the period of its first exposure? A small galvanic arrangement having been made by placing a tube, closed at one end with a skin diaphragm, in a large test glass; a solution of the iodide of potassium was poured into the tube, and a solution of nitrate of silver was put in the outer glassthe two fluids being connected with a piece of platinum wire. An arrangement of this kind being placed in the dark, in about four hours a very beautiful crystallization of metallic silver was found to have taken place about the platinum wire in the silver solution. Another arrangement, in every respect prepared in the same manner, was exposed to sunshine. Not only did no metallic crystallization take place whilst exposed, but the exposure had so changed the character of the solution, that no such crystallization would afterwards take place, even in darkness. This experiment was many times repeated, with various modifications, but always with the same result. Here we have a very striking instance of the interference of the solar radiations, with the exercise of the force of galvanic electricity. It is not improbable, but these may be made measurers of each other; knowing the force of the current generated between the two solutions, it will not be difficult to ascertain the quantity of the solar rays necessary to retard or stop the action of that force. Another experiment was as follows:-a solution of the bichromate of potash, and a solution of the sulphate of copper being mixed together, were exposed to the sunshine, and such light as might prevail during the month of November. A similar solution which had not been so exposed, was evaporated, and crystals obtained of a rather curious character. They were sulphates of copper and potash, and salts of chromium, which had not been previously described. On evaporating the solution, which had been exposed to the sunshine, it was found that the characters of the crystals were completely changed, as far as chemical combination was concerned. The relative proportions of the constituents being in each case very materially changed. Similar results had been obtained with solutions of the bichromate of potash, and the chlorides of gold, and of mercury. The investigation is not, however, yet complete. Mr. Hunt exhibited several specimens of the salts prepared from both the exposed and the unexposed solutions.-Annual Report of the Royal Cornwall Polytechnic Society, 1844. MR. BIRAM'S STEAM-VESSEL LOG. Sir,-From Mr. Curtis's observations, at the Institution of Civil Engineers, in the discussion after Mr. Guppy's interesting paper as to the uncertainty of measuring a ship's velocity by the common log, I am induced to obtrude my invention once more upon your notice, as being an exceedingly simple mode of ascertaining to a great nicety the relative performances of steam vessels, and also as a substitute for the log. Fig. 1 is a side view, and fig. 2 an end view of this instrument. A is a small wheel, 1 foot diameter, having vanes set at such an angle, that, when let into the water, the action upon their inclined surfaces would cause the wheel to revolve once in passing the distance of two feet through the water. Upon the axis of the wheel is an endless screw, a, into which works a small toothed wheel, having 51* teeth. The instrument should be mounted on the low end of a stiff bar of wood, or other material, of such length, as that the top end could be fastened by a joint or hinge, b, to the side of a vessel, in convenient proximity to a cabin window, or to the deck. To the low end of the rod or bar a small line should be attached, c, the other end of which to be secured on the deck of the vessel. use of this line would be to withdraw the instrument from the water, when not required for observation, and to lash it horizontally out of the reach of the waves. When the line was released, the instrument should be so suspended as to fall perpendicularly into the water, and the bar sufficiently stiff to remain perpendicular, and resist the pressure of the water against its front edges, which, however, would be but trifling. The axis of the small toothed wheel should be enclosed in a tube in front of the bar on which the wheel is suspended, and prolonged to a short distance below the hinged joint; and upon the top end of it should be fixed an index, d, to revolve on a dial-plate decimally divided. The wheel being constructed as before described, this index would make one revolution round the dial-plate in the time that the vessel passed 102 feet through the water, which is about the * Probably 50 teeth would be better. The 66 one-sixtieth part* of a knot, or nautical I have now by me a small wheel constructed as here described, which I should have great pleasure in forwarding for the inspection of any person interested therein. This wheel has eight vanes, which are retained at their proper angle by a ring which surrounds them; but I think six, or probably a less number, would be sufficient, and that they might be made sufficiently strong to retain their shape without the ring, which would reduce the friction. In a steam vessel this instrument should be fixed before the paddles. I hope the accompanying sketches will be sufficiently explanatory. I am, Sir, BENJAMIN BIRAM. Wentworth, September 17, 1845. CYLINDRICAL AND CONIC SECTIONS. Sir, I beg to correct an error in my last. I have there stated that the winding intersection of the solids adverted to, cannot have more than three points on the same plane. I ought to have said, may have always three points on the same plane. In the intersection (alluded to in vol. xliii. p. 143) of the cylinder and cone, there may be four points of the curve of intersection on the same plane. The number of points that may be in the same plane, of winding curves of intersections, may be an important matter in the mathematical consideration, in the projection of the whole, or part of such a curve on a plane, and in the mechanical application of the motion, by which such lines can be drawn. In the case just alluded to, the axis of the cylinder and the axis of the cone Rather more. 217 are in the same plane, and the curve of intersection is in two parts symmetrical. But, if the axis of the one is on a different plane to the axis of the other, the line of intersection will be dis-symmetrical. Without having a sufficient number (perhaps some hundreds) of cones and cylinders intersected in the various distinct ways they will admit of, and these on a sufficiently large scale, (and also transparent, would be desirable,) it is difficult to comprehend, and more difficult to describe, the exact appearance of every distinct line of intersection as it might be projected at different angles; or from one of the curves of the " Septenary System," to show in what way a cylinder and cone should be intersected, so that viewed or projected at some angle the intersection would be the same line. With a sufficient number of these practical intersections, the difficulty would be removed, and correct rules deduced for practical applications. I am, Sir, yours, &c. JOSEPH JOPLING. 29, Wimpole-street, Sept. 17, 1845. THE AMERICAN FRIGATE PRINCETON." [Extract from Report of Committee of the American Institute appointed to examine this frigate. The ship is 164 feet in length, 30 feet beam, 22 feet hold, making her about 700 tons measurement. She draws 17 feet of water aft, and 14 feet forward. The peculiarity of her construction is great sharpness of entrance and run, with nearly flat floors midships, which effectually prevent her being crank, notwithstanding the great weight of her battery. The most obvious peculiarity of the Princeton's model is the great extent of her dead-wood, terminating with a sternpost of unusual thickness, being 26 inches through at the centre of the propelling shaft, but tapering both above and below. The object of this uncommon form is to give sufficient strength to the stern-post, as a hole of 13 inches diameter passes through it, in which the propeller shaft revolves. The sternpost also requires unusual strength, because the bearing which supports the whole weight of the propeller is attached to it, the shaft having no bearing abaft the propeller. The rudder is of an entirely novel construction, consisting of a frame of wrought iron, filled in with 5-inch pine plank, the whole of which is cased with copper plates, threesixteenths of an inch thick, thus making the entire thickness of the rudder 5 inches. The mode of supporting the rudder is equally novel. It is hung to an outrigger of wrought iron, covered with half inch copper plate, the upper part being attached to a strong oak knee under the counter, and the lower part being attached to a solid frame of oak timber, 3 ft. 6 in. wide, and 14 inches deep, firmly bolted to the after part of the keel, and dead-wood of the ship. The thickness of the outrigger is 5 inches, the same with that of the rudder, measuring 2 feet fore and aft, the forward part being made as sharp as a ploughshare. This sharpness, and the thinness of the rudder, prevent the current produced by the propeller from retarding the progress of the ship. Your Committee examined with particular interest and attention the steam-engine of the Princeton, which excited their admiration no less by the novelty of its construction than by the perfect symmetry and beauty of its proportions. It is styled by the inventor and patentee, Capt. Ericsson, the Semi-cylindrical Steam-engine.' It has been constructed apparently with two main objects-that of being placed entirely below the water line, and of giving a direct motion to the propeller shaft, which requires a greater velocity than can be obtained by the ordinary engine. These objects have been fully accomplished; indeed, so compact is the engine, that its highest point is placed more than 4 feet below the water line, and so far below the berth deck that it affords space for lodging from 2 to 3 feet of coal above it, as well as on the sides. The peculiarity of this engine consists in the use of semi-cylinders instead of entire cylinders. These semi-cylinders are 72 inches in diameter, and 8 feet long. The pistons are parallelograms attached to wrought iron shafts, forming the axis of the semi-cylinders, and are made to vibrate through an arc of 90 degrees, by the admission of steam alternately on opposite sides, ordinary slide valves being employed for that purpose. The piston-shafts pass through stuffing-boxes at each end of the semicylinders; and at the forward ends crank levers of 34 inches throw are attached, which, by means of connecting-rods only 74 inches in length, give motion to the main crank of the propeller shaft. The active surface in each piston measures 96 inches by 26, presenting an area of 2496 inches. The centre of pressure of each piston moves through an arc of precisely 36 inches, and thus the Princeton's engines have equal power with two ordinary marine engines having cylinders of 563 inches diameter and 3 feet stroke. At the opposite ends of the piston shafts, crank levers of 16 inches throw are attached, for the purpose of giving motion to the air pumps and force pumps. Your Committee cannot refrain from noticing particularly the ingenious disposition of the working parts connected with these pumps, and the remarkably simple mode by which the requisite parallel movements are obtained. The maximum speed of the engines is thirty-seven revolutions per minute. The maximum pressure of steam in the boilers is twenty-five pounds to the square inch; and the steam in the semi-cylinders is invariably cut off at one-third of the stroke. The greatest speed of the vessel, as ascertained by Captain Stockton in the Delaware, has been nearly fourteen statute miles per hour. At the ordinary speed of twelve miles, the consumption of fuel has been found to be eighteen hundred pounds per hour. SO It is necessary only to allude to the propeller of the Princeton, constructed by Capt. Ericsson, and identical with that now successfully employed in various parts of the country. This propeller is manufactured of composition metal. Its extreme diameter is 14 feet, and the upper part is full 3 feet below the water line. The boilers of the Princeton are also placed below the water line, and resemble those of the ordinary marine engines; but their furnaces and flues are so constructed as to burn anthracite as well as bituminous coal. Attached to the boiler is a heating apparatus possessing very remarkable properties, by which the water feeding the boilers is constantly heated before entering the same. Your Committee view this apparatus as perhaps the greatest improvement of which the low pressure engine for ship use is susceptible. It not only continually supplies the boiler with hot water, but enables the engineer, when at sea, to blow off' very freely, without any material loss of pressure or expenditure of fuel. The smoke-pipe of the Princeton is constructed upon the principle of the telescope, and may be elevated in lighting the fires, or when it is desirable to work the engines with natural draft. The contrivance made for this purpose is efficient, being a simple application of the endless screw, turned by a crank; and it enables two men to raise and lower the chimney with great facility, precluding the possibility of an accident from negligence, as the smoke-pipe will remain stationary, whenever the men at the 66 THE AMERICAN FRIGATE hoisting apparatus discontinue working it. The successful introduction of this sliding smoke-pipe, and the means for elevating and depressing it, must be considered a complete solution of one of the many problems connected with naval warfare hitherto unsolved. The fire draught is independent of the height of the smoke-pipe, being promoted by centrifugal blowers placed in the bottom of the vessel, and worked by separate small engines. Thus the steam machinery of the Princeton realizes all that can be desired for a war steamer, as the whole of it is placed out of the reach of the enemy's fire. Your Committee would do great injustice to the manufacturers and the vast progress in the mechanic arts, recently made in the United States, if they omitted to refer, in language of the highest pride and gratification, to the beautiful workmanship and execution of the steam machinery of the Princeton. It more than rivals-it surpassesthe machinery of the trans-Atlantic steam ships. It was built by Messrs. Merrick and Towne of Philadelphia. The armament of the Princeton consists of twelve 42 pound carronades, and two 212 pound Stockton guns. These last are made of wrought iron, said to have been thoroughly proved, and all are placed on the upper or spar deck. One of the Stockton guns, weighing fourteen thousand pounds, is placed eight feet forward of the mizenmast, and in a line with it; the other, weighing twenty-three thousand pounds, is placed at the bow*. Both are mounted on carriages traversing on beds of timber, which are secured in the centre by strong pivots, around which they turn. These beds are supported by four friction rollers, inserted in the four corners, and travelling on a flat ring of composition metal let into the deck. The bulwarks, being moveable and very light, are readily unshipped, to give full play to the large guns in the direction required. The carriages are made entirely of wrought iron, each side being composed of two plates, ths of an inch thick, 4 inches apart, and connected by a series of stay bolts. In the space between the two plates, a simple mechanism is ingeniously concealed, which enables four men with the utmost facility to roll the guns back and forward on the beds, and removes altogether the anticipated diffi It was the last of these guns that subsequently exploded, (see Mech. Mag. vol. xlii., page 47,) and which has been since replaced by a gun of the same size, but better metal, manufactured by Messrs. Fawcet, Preston, and Co. of Liverpool.-ED. M. M. culties in managing ordnance of such immense calibre. It need hardly be stated that the difficulty of checking the recoil attending the heavy charge necessary for such à piece is even greater than that of moving the gun, and here again mechanical skill has triumphed to all appearance over the supposed insuperable obstacle. The ordinary breeching is entirely dispensed with, and the recoil is checked by opposing a gradually increasing friction to the carriage on which the gun is mounted. The means employed for this purpose exhibit a happy application of one of the fundamental principles of mechanics-that of the inclined plane, in connexion with the laws of friction; and so successfully has this principle been applied, that although the friction apparatus, at the termination of the recoil of the gun, becomes what is technically called jammed, with a force perhaps of many millions of pounds, yet by slightly touching a lever, it becomes instantly disengaged, leaving the gun and carriage perfectly free. A contrivance having the same object in view is applied to the carronades, which in them also dispenses with the ordinary breeching. In connexion with the Stockton guns, besides the carriage, &c., of which they have spoken, your Committee have to notice two other contrivances, which render them unquestionably the most formidable ordnance ever mounted. Of these, the first is a lock so constructed that it is discharged at any desired elevation, without human interference, by a peculiar mechanism, in which the law of gravitation, in connexion with the rolling of the vessel, is rendered subservient to this purpose. The second contrivance referred to is an instrument to measure distances, by which the requisite elevation to be given to the gun may be instantly determined. Your Committee would mention that the heaviest of the Stockton guns was forged in the city of New-York, by Messrs. Ward and Co., and was bored and finished by Messrs. Hogg and Delamator, of the Phoenix Foundry. It is composed entirely of American iron, and is, beyond comparison, the most extraordinary forged work ever executed in this or any other country. The Princeton is sparred and rigged in the ordinary manner of sloops of war. All the modern improvements of our packet ships have been adopted, and in some cases simplified. It is therefore believed, that as a sailing ship, without reference to her engines, she will be found to be very fast, and to excel in that respect anything of her size yet built for our Government. This quality will enable her to keep the sea as long as any other corvette, and at no greater expense |