as a liquid, we may safely assume that the point of fusion is at the top of the hearth in hot-blast furnaces.

With the object of rendering these processes more intelligible, we have shaded a section of the furnace so as to represent the different parts employed in their special functions, the drawing being made to an exact scale. A B is the space in which the distillation proceeds, BC and CD show the region in which the reduction of the ore and evolution of the carbonic acid are effected, and in which the materials attain the temperature necessary for fusion.

The marked difference between the results obtained in the continental furnaces and those in this country will cease to excite surprise, when we bear in mind the different nature of the fuel employed. The principal reason of the great depression of the region of reduction in the furnaces of this country, is that almost all the body of the furnace is taken up in the process of coking; and hence the point of reduction must be still further lowered if the pieces of coal be of a large size. These pieces, often in bulk equal to a cubic foot, must remain a long time before the heat penetrates thoroughly through them, and the column of air ascending through this material must yield its heat in order to render gaseous above 30 per cent. of the fuel. Hence the depression of the temperature of the upper half of the furnace becomes so great that it does not suffice for the reduction of the ore, nor is it sufficient for the expulsion of carbonic acid from the limestone. Another important cause lowering the region of reduction, is the high pressure at which the blast is thrown into the furnace, the pressure being six or seven times the amount of that used in Germany. The materials, on this account, traverse through the furnace much more speedily, and therefore require to pass through a larger space to become heated. All these circumstances have much less influence in the German and Swedish furnaces. The charcoal with which the latter are fed is a fuel almost completely coked, and the materials, being in small fragments and thoroughly mixed, offer a heating surface at least a hundred times greater than that exposed in English furnaces. The small pressure of the blast also effects a slow combustion, so that the fuel frequently takes twice or three times the period to pass through the same region of the furnace.

To be Continued.

Description of Venitian Blinds Patented by JOHN HAMPSON, ESQ., Civ. Eng., of Carrollton, Louisiana, August 21, 1841.

The frame is made in the ordinary manner, with the exception of the inner edge of one side being rabbited, so as to allow a movable strip, a a, (see sketch,) to be placed therein, of about 3 in. in thickness, and of such width as to allow holes to be made in it, for the pivots or journals, e e, of one end of the slats to work in. In the edge of the frame at the bottom of the rabbit, holes are bored, in which brass wire spiral springs, India rubber, or other elastic material, are placed, as shown at b b; these springs keep the strip a a close up to the end or shoulders of the slats, with just sufficient pressure to retain them in any position in which they may be placed, and prevent them from rattling or shaking down when they are

used in railroad cars or carriages. To keep the strip a a in its place, and to hide the springs, a flat strip, (of the same kind of wood as the frame is made of,) d d, is let in and fastened with screws, as shown. This flat strip need not be over in. thick; it may be stronger if required. It is evident that, if the pivots be somewhat smaller than the holes in which they work, the weather cannot affect the movement of the slats; it is also evident that the frame may be fastened together before the slats are put in, which is not the case with the common blind, and which give great facility in repairs in case of accident.

The patentee claims the method of preventing the slats from rattling, and retaining them in any position in which they may be placed, by means of the movable strip or strips pressed up by springs or other elastic sub

The patentee says: "This blind has been in use in railroad cars, in and about New Orleans, for over seven years, and has given universal satisfaction. In simplicity, comfort, durability, and economy, it is all that can be desired. It is applicable wherever movable or rolling slat Venitian blinds can be used. Rolling slat Venitian shutters are desirable in many situations, and there is little doubt but that many more would be used were they (as commonly made) less troublesome and unmanageable. All

the objections that are made to the common rolling slat Venitian shutter, are removed by this improvement. The extra expense on each car blind does not exceed 20 cents, and on house blinds it would not exceed 80 cents for a window—a mere trifle in comparison with the comfort and durability."

For the privilege of using this improvement, apply to JOHN HAMPSON, Engineer and Superintendent of the New Orleans and Carrollton Railroad.

To the Committee on Publications.

Account of the Explosion of the Steam Tow Boat Defiance.

NEW ORLEANS, JUNE 10th, 1849.

GENTLEMEN,-Agreeably to your request, I forward the best information I could obtain after the receipt of your letter; at the time of the explosion, my engagements prevented me from investigating this matter, although anxious to do so.

The Defiance (belonging to the Independent Tow Boat Company) is a new boat, her engines and boilers were built by Messrs Shield & Co., Cincinnati. The boilers I suppose were made from drawings furnished by Mr. Montgomery, (who claims the plan,*) as they are similar to a pair made here for him, which were tried and condemned; I mention this as these have the same weakness, which in my opinion was the cause of the Defiance's giving way.

Coming down the river the boilers performed well, indeed they could not do otherwise, for in addition to being new, there is a large amount of fire surface; it is said that the boilers foamed much; this is reasonable, for the water is greatly subdivided.†

The external appearance of the boilers before injury, was similar to many of the so called low pressure ones. Internally, the fire acts on two arched crowns or flues, the flame passing back over a water bridge pipe (the end as shown by the dotted lines) to a chamber, a, and there it is diffused and circulates around 600 vertical tubes, (1 inches in the clear,) before it enters the chimney; the lower ends of these tubes (a few are seen at b) are connected with a sheet forming the top part of a water bottom, c; the upper ends of the tubes are secured to a "table" or head sheet as shown in the sketch; these tubes, along with the water sides or spaces, (3 inches in the clear,) forming a free communication for the circulation of the water. The attachment for the supply pipe is at d. The lowest of the

I have in my possession a sketch, taken from a boiler, made by Mr. Holloway of your city, and put in the Thomas Jefferson, a low pressure boat, at Norfolk, Va., in 1833. The only difference is that in this boiler (Holloway's) the vertical water pipes are of larger diameter, and fewer in number, advantages that practice will lead to in this, otherwise its action was exactly similar to this patent one.

†The boilers having none but the ordinary gauge cocks, it would be very difficult to know the exact height of the water when foaming. In 1833, I had an English locomotive in my charge, which would show water at the upper cock, when there was not twenty gallons of water in the boiler; (I then devised the plan of gauge chamber, see p. 94, vol. xx1, 2d series, I think a republication of this would do good, as I and others have used it often since, and find it to be all that is desired; see also July number, 1841, page 14.)

gauge cocks, e, are 2 inches above the table or head sheet, the middle ones 2 inches higher, and the top cocks 23 inches above the middle ones. The boilers were not displaced by the explosion, and, as will be seen by the diagram, they present nearly the same appearance as when viewed end on.

The Defiance started on the 24th of March, at 11 o'clock at night, with her first tow, having one ship on each side, and another astern; they ran slow through the night, on account of fog, but had increased her speed when it became clear, not long after the watch was changed, at 8 A. M.; the chief engineer (who is said to have been a very careful man) coming on duty, had tried the gauge cocks, and found the water "fair," and was in the act of passing from the boilers when they bursted, and he was thrown against a brace which caused an internal injury, of which he died a few hours afterwards. I suppose that the starboard boiler, (which is the one sketched,) gave away first, followed almost instantaneously by the other; the report was of a "dull sound." The force and direction of the bursting was upwards, and towards the starboard side, as part of the top of the starboard boiler, with the steam drum, etc., passed over the ship on that side; the boat having headway at the time, part of the fragments which ascended vertically, fell on the deck of the stern tow; much water in nearly a cold state fell on the deck of the Defiance. As a matter of course, all that was above the boilers, including the man at the steering wheel, were carried away; this is the seventh time of this steersman being tossed in the air, under similar circumstances, with scarcely any injury.

In this case, along with many others, an explosive gas has been lugged in to account for the bursting; never having been a believer in this theory, I will give something more tangible to account for the bursting. The semicylindrical shell being 9 feet in diameter, and only of an inch in thickness, without stays or other adjuncts, is at once seen to be too light for a working pressure ranging from 100 to 150 lbs. to the square inch; now to this first want of strength, an unnecessarily large hole (22 x 14 in.) is made for the man head rim, (a fragment is seen at f,) and another for the steam drum g; and to weaken the shell still more, yet another hole was cut for the safety valve (at h,) which would have been better on the top of the He may have been deceived, but the want of strength of the shell, was sufficient cause in itself.

steam drum; all the holes being enclosed within the space of a few feet, it requires no fancy to suppose that the starting point of rupture was at the man hole, taking the other two holes in its course; when once ruptured, then running down the line of rivets and straightening out the sheets, as is common in explosions of this form of boiler. Part of the top of the back of the shell, like a hood, is thrown over, as is seen at i; a small piece of the shell of an irregular form, with the safety valve (which is of ample size) attached to it, is bent over towards the front, as seen at k; the blow from the casting has caused an indentation on the top of the shell. Along side of it is seen part of one of the fore and aft stays (1 in. in diam.) the plate part at 1, having been torn from the back end of the boiler.

Along the lap edges of the shell, much of the iron is broken short, while a small part has the appearance of being torn; some of the match holes in each sheet, as at mm, are perfect, the rivets giving way without injury to the sheet. All the internal parts, with the sides, ends, and top part of the shell immediately over the arches, (which are well stayed, remain uninjured.

I am not one of the advocates for making boiler plates very thick, believing that their imperfections keep pace with the thickness, but prudence and experience should have prevented the using as light iron as this. It is not a usual practice to use stays for the shell of a boiler, as they are objectional; but I think that when the boilers are of this form, and of large size, using high steam, that ribs of angle iron passing over the top, down to each side and riveted to the sheet, would be beneficial, as, if the boiler did give way, it would prevent the large opening always made, and reduce some of the destruction consequent to an explosion.

Respectfully yours,

A. C. JONES.