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.t

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, (12 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. xxI, 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 24 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.

b

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 gi 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.

Mode of Extinguishing Fires in Coal Mines.

For the following interesting account of the successful result of an experiment made to extinguish a fire in the coal mine of Mr. Darlington, at Astley Collieries, near Manchester, we are indebted to the Times. Mr. Darlington, who is the author of the communication, writes as follows:"On Monday, the 2nd of April, one of my coal mines, at Astley, was discovered to be on fire, and had spread to such an alarming extent as to prevent all access by the usual shafts. We immediately put out all the fires about the works, and requested the cottagers in the neighborhood to do the same, for fear of an explosion. The plan of procedure in such cases (which happen more frequently than those unacquainted with collieries suppose) is, first to stop down all openings into the mine, so as to prevent any access of the atmosphere. If, after some time, the fire is found not extinguished, the only alternative is to fill the mine with water from some source in the neighborhood. In the absence of a sufficient reservoir of water, the pumps are stopped, and the water allowed to accumulate from the natural drainings, generally an unsatisfactory and slow process. In the former plan, notwithstanding every precaution is taken in sealing the shafts, it is found by experience that air in small quantities will oe drawn through the stoppings and fissures of the earth sufficient to keep up a slow rate of combustion for a very long period. We have proof of this in many instances occurring in this neighborhood. In the extensive collieries worked by Lord Bradford, at Bolton, the mine has been on fire nearly two years. When the fire happened, it was sealed up for some months; but, on opening it, the fire was found still burning. The pits were again immediately sealed up, and left to remain for twice the former period. On opening the mine at this time the fire burst out as before. It was again closed, and so remains to this day. At the collieries of the Earl of Ellesmere, at Worsley, one of the mines took fire about the same time; it was treated in the same way; it is still on fire; and, at this moment, his lordship is about to turn in the Bridgewater Canal. In the Patricroft Colliery, the deepest mine in this county, a fire broke out in the upper part of the workings, which baffled every attempt to extinguish it, and is now stopped up and abandoned. At Mr. Blundell's colliery, at Blackrod, in this district, the pits were opened after being closed some weeks, on account of fire, when a fearful explosion took place, and did considerable mischief to the workings. The fire burned with greater intensity than ever: the flames rose out of the mines, set fire to the head-gear, and burned so fiercely within the pit that it actually melted the iron tram-wheels. In this case the River Douglas was eventually turned into the workings so as to fill them with water. I could mention several other cases in this immediate neighborhood, to show the importance of the question before us, and the difficulties we have to contend with when these unfortunate accidents occur. In our case we instantly sealed up the mine, yet fire-damp issued from every crevice about the stoppings, and through orifices in the earth, in such quantities that the safety lamps would take fire at a considerable distance. In this state of things I wrote to Mr. Goldsworthy Gurney, (whose application of high-pressure steam to the ventilation of coal mines

is exciting so much interest,) stating the case, and asking if he could point out any plan, by high-pressure steam exhaustion, or otherwise, likely to be of service. Mr. Gurney immediately came down, and after well investigating the conditions, in consultation with us, proposed to fill the mine with carbonic acid, azote, or some other extinguishing and incombustable gas. This, at first, appeared to us impracticable, the immense quantity required to fill the galleries and lateral workings, together above three miles in length, being too expensive, if it were possible to obtain it, to warrant the proposition. He, however, soon set us right. He said nitrogen, or azote, might be obtained from the winds of Heaven, and carbonic acid from the coals lying waste about the pit, assisted by a little charcoal and lime; air would be deprived of its oxygen by being passed through burning charcoal, coal, coke, and small coal, and the azote set free. In short, the product of this combustion would be the choke, or black damp known in mines. We immediately built a furnace of brickwork four feet square, at a safe distance from the downcast shaft. To the ashpit, in every other respect made tight, an iron cylinder thirteen inches in diameter was connected, and made to terminate at an elbow under water in a close tank partly filled. With the upper part of this tank, above water, another pipe was connected and carried through the stopping of the downcast pit. A powerful steam jet was made to work between the furnace and the tank, which drew the air down through the fire, and forced it through the water. A second jet was placed in the cylinder at the top of the down cast shaft, and made to draw the choke-damp from the tank, and force it into the pit. At the other, or upcast shaft, we placed a jet in a cylinder, communicating, through the stopping, with the mine, for the purpose of exhausting the shaft beneath and thereby assisting the compressing jets to drive the choke-damp through the galleries. The apparatus thus fitted, as soon as the fire in the furnace had burned up, was set in action. In order to test the effect of the choke-damp, we placed some burning tow, moistened with spirits of turpentine, into it. The flame was as instantly extinguished as if it had been placed in water. It was thus tested in the cylinder, as it passed from the ash-pit, before coming to the jet, and also in the tank and second cylinder, with similar results. This was conclusive evidence of the perfect formation of the choke-damp. In about two hours after the jets were set in action, fire-damp disappeared from the shafts, and we observed a slight cloudy appearance in the escapage from the upcast shaft. It had the sulphurous smell of choke-damp, which pervaded the air to a considerable distance. A safety lamp was now brought and placed in the upcast cylinder; it became instantly extinguished as if put into water. For this purpose the draughts were momentarily shut off. A bright burning fire of charcoal, in a chafing dish, was placed in the escapage at the cylinder, and was also immediately extinguished. These facts satisfied us that the choke-damp had passed through the mine. The period of its appearance agreed with our calculations. The quantity of choke-damp forced through the mine was about 6000 cubic feet per minute, and this would fill the galleries in about that time. The choke-damp was allowed to remain for several hours, at the termination of which we were convinced that all fire, however intense, must be extinguished in the mine. The connexion with the furnace was