received in experimenting, by which the ultimate application was arrived at, are carefully set forth for the guidance of future practitioners. We have therefore felt it highly desirable to report, as accurately as it is possible, a few particulars as to the failure of the Bridge over Joiner-street, at the carriage entrance to the South-Eastern Railway Offices of the London Bridge Station, which took place on Saturday, the 19th ultimo.

The bridge is of a peculiar construction, and consists of six compound girders of cast and wrought iron, patented by Captain Warren. The annexed engraving, fig. 1, shows part of one of the girders, rather more than half the length; and fig. 2, a transverse section of the roadway and two of the girders. There are in all six girders, placed 11 ft. 6 in. apart. .The girder that broke is 41 ft. 6 in. long, and consists of a series of triplet cast-iron triangles, with a connecting-rib along the top and bolted at the joints, but there is no connecting-rib along the bottom of the girder; instead of which, they are held together by a horizontal tie, consisting in width of four wrought-iron bars, 6 inches deep by 14 inch thick and 13 feet in length, coupled together by 43 inch bolts passing through a boss cast on the triangular stays, and also bolted to the intermediate triangles.

The cast-iron triangles are 4 feet deep, with a rib cast on the top 6 in. deep, making the whole height of the girder 4 ft. 6 in., and the length of the triplets 13 feet; the section of the cast-iron is T-shaped, 5 inches wide on the back, and the depth the same; the thickness of metal 2 inches.

On the top of the girders are laid cast-iron plates, 11 ft. 6 in. long, with ribs bearing at each end on the girders; on these plates rest the materials which form the road, as shown in fig. 2. It must be observed, that the horizontal tie-bars are not intended to act as suspension bars; they are merely connected at the abutment piers to the ends of the cast-iron triangles. The points at which the bridge failed is marked with the letter f, where one of the cast iron stays broke asunder, and also the top rib, as shown in fig. 3, which is an enlarged view of the triangle which failed. It was only 5 feet from the abutment. The fracture is shown at f,f,f. Various statements have been made as to the cause of the failure.

It was stated that the accident was caused by the girder being loaded with a large stack of bricks; but this is doubted, as the stack was at the opposite end, as shown in the annexed diagram. The stack of bricks

bearing on the girder was 11 feet square and 5 feet 6 inches high, equal to 666 cubic feet, which will give, at 72 feet to the thousand, between nine and ten thousand bricks, or a weight of about 22 tons. Another statement is, that the failure was caused by two carts which were on the bridge at the time; one of them, loaded with bricks, it is supposed passed over some obstacle, and caused the wheel to descend suddenly with great force. Whether this be so or not, we cannot pretend to say; but if the bridge had been properly constructed, with a cast iron girder 41 ft. 6 in. long, and of the great depth of 4 ft. 6 in., it ought not to have broken down with any such force. For ourselves, we are decidedly averse to these compound girders of wrought and cast iron. The contraction and expansion are unequal; and, consequently, the strain must be constantly varying, while the slightest deflexion of the wrought iron must cause the cast iron to snap asunder.

If this bridge had been constructed with a series of triangles, cast with a connecting-rib at the bottom and a broad flange on the underside equal in weight to the wrought iron, it would, in our opinion, have stood and borne a weight far greater than this compound girder bridge.

At the time we went to press, they were testing the bridge, and had a dead load when we left of 30 tons on a pair of girders. With a load of 20 tons on the pair, the deflexion was 0.20 of an inch.

Figs. 1 and 2 are drawn to a scale of 4-in., and fig. 3 to 4-in. to a foot.

Our English friends and their imitators here, are much shocked at the carelessness and mismanagement on our railroads, and it must be confessed not without cause. How will they like the following as a matter of comparison?

Lancashire and Yorkshire Railway-Frightful Collision.*

On Friday last, about six o'clock, a fearful collision took place on this line, near the Huddersfield Junction, by which an immense amount of damage has been done to the stock of the Company, three engines being destroyed and a train of carriages knocked to pieces. The accident appears to have arisen as follows:-An engine which had been undergoing repairs in the engine shed on the main line, close to the junction, was being driven on, in order to its being shunted on to the line on which it was to be worked, and by some singular mismanagement was brought into violent collision with the passenger train from Bradford. The shock was so violent as to smash completely the engine and tender as well as * From the London Railway Magazine, for November, 1850.

the engine belonging to the passenger train. The passengers, in alarm, jumped out of the carriages, but had hardly time to become conscious of their fortunate escape when a goods train dashed into the standing train, doubling up all the carriages in a moment and knocking them to shivers. It was remarkable that none of the passengers were killed or injured by the flying splinters. The line was completely choked up, and men were immediately set to work to make a temporary line of rails for the transit of the usual traffic. It is impossible, at present, to estimate the extent of the damage. An inquiry will be promptly instituted into the circumstances connected with the catastrophe, Capt. Laws having repaired to the spot immediately on receipt of the telegraphic news of the accident.

For the Journal of the Franklin Institute.

Advantages of using Fresh Water in the Boilers of Sea Steamers.

In steam boilers using salt water, it is necessary to extract or blow out a portion of the partly saturated water, at intervals or by a continuous process, to prevent a deposit of solid matter on the internal surfaces. The water blown out or extracted being much hotter than when it entered, must be the cause of an increased consumption of fuel, and may be explained or estimated as follows:

Sea water contains about one pound of salt and other solid matter in every 32 lbs. of water; its density is then called, being ad part of salt, &c. When reduced by evaporation to half that quantity, the same amount of salt is still in that water, and is then in the proportion of 2 lbs. of salt to 32 lbs. of water, or at the density of 2, &c.

It is evident that when keeping the water in the boiler at a density of 32, one part is used for steam, and an equal quantity must be blown out; then as much salt, &c., will go out in one gallon or foot as entered in two gallons or two feet, and as long as this proportion to that evaporated is blown out, the water in the boiler will be kept at that density.

If the water in the boiler is kept at the density of 332, then two parts will be used for steam, and one part must be blown out; then as much salt, &c. will go out in one part as entered in three parts.

Taking the latent heat of steam at 990°, sensible heat 212° -1202°, the total heat in steam.

The quantity of heat necessary to evaporate one volume of water, is 1202°, less the temperature of the feed water entering the boiler, which is generally about 100°; taking this from the sensible and latent heats =1202-100=1102°, which must be imparted to it to cause it to assume the form of steam.

The part or water blown out has to be raised from the temperature of the water entering to that leaving the boiler. Water entering 100°, that blown out 250°, difference or loss, 150°.

The proportion or loss is shown as follows:-Suppose two volumes of water enter the boiler, and the density is to be kept at 2:

One volume is formed into steam and requires

One volume is blown out containing

Quantity of heat required

1102°

150°

1252°

The 150° blown out, being necessary to keep the boiler from incrusta

tion, is the part lost; therefore,

1252
150

If the water in the boiler is kept at 32, then, if three volumes of water enter the boiler, two are formed into steam.

The following formula will answer for calculating it:

Let H represent the sum of the sensible and latent heats.

D the difference in temperature of the water entering and that leaving the boiler.

T the temperature of the water entering the boiler.

E the proportion or quantity of water evaporated, the quantity blown out being constant, or represented by 1.000.

H-T×E+D

= the 1 part of the heat lost.

Then

Ꭰ

D

Or

= the

H-TXE+D

per cent. of loss.

The following is calculated by this formula:

Example for the Density of 15.

H=1202°

At 1:75

32 2

At
At 2.25

32

T-100° E=5 D=150°

Per cent.

1202-100-1102x·5-551+150-150 21-39

1202-100=1102×1+150

At 331202-100-1102x1.5+

32.

The amount of loss stated above occurs when enough is blown to keep the water at the densities given. To keep the boiler clean, the water should not be allowed to get more dense than in the Atlantic Ocean, but, to be sure, it should be kept rather less in the Gulf of Mexico-not more than 5. In steamers having no indicator of this kind, they very probably keep the water less than 5, and most of them that have them keep it at 175, with a loss of from 14 to 21 per cent. of fuel. The above proportion of loss is when steam of two atmospheres is used; the loss increases as the pressure of steam used is greater, in consequence of the water being blown out at a higher temperature.

329

The saving in the cost of the fuel is but a small part compared to other advantages, such as increased durabilty of boilers, greater safety, increased stowage of freight, &c.

W. S.

90

Extract from an Account of the Chimney of the Edinburgh Gas Works,. with observations on the Principles of its Strength and Stability. By GEORGE BUCHANAN, ESQ., F. R. S. E., C. E.*

The only point remaining to be considered, and to which Mr. B.'s attention was particularly called, was the expediency of protecting the building by a lightning.conductor. He had formerly, when the old chimney was erected, been consulted as to this, and considered it unnecessary, height being moderate, and doubts being then entertained of the efficacy or expediency of such instruments. Much, however, has since been added to our knowledge and experience on this subject, and on the beneficial operation of conductors; so that he had no hesitation, the altitude also being so much greater, in recommending it. But having requested to be favored with the views of a friend, and high authority, Professor Faraday, he gave an extract from his letter as follows:

"The conductor should be of 4-inch copper rod, and should rise above the top of the chimney by a quantity equal to the width of the chimney at top. The lengths of rod should be well joined metallically to each other, and this is perhaps best done by screwing the ends into a copper socket. The connexion at the bottom should be good; if there are any pump-pipes at hand going into a well they would be useful in that respect. As respects. electrical conduction, no advantage is gained by expanding the rod horizontally into a strap or tube-surface does nothing, the solid section is the essential element. There is no occasion of insulation (of the conductor) for this reason. A flash of lightning has an intensity that enables it to break through many hundred yards (perhaps miles) of air, and therefore an insulation of 6 inches or 1 foot in length could have no power in preventing its leap to the brickwork, supposing that the conductor were not able to carry it away. Again, six inches or one foot is so little that it is equivalent almost to nothing. A very feeble electricity could break through that barrier, and a flash that could not break through five or ten feet could do no harm to the chimney."

"A very great point is to have no insulated masses of metal. If, therefore hoops are put round the chimney, each should be connected metallically with the conductor, otherwise a flash might strike a hoop at a corner on the opposite side to the conductor, and then on the other side on passing to the conductor, from the nearest part of the hoop there might be an explosion, and the chimney injured there or even broken through. Again, no rods or ties of metal should be wrought into the chimney parallel to its length, and, therefore, to the conductor, and then to be left unconnected with it."

In answer to some further inquiry, Professor Faraday again writes:— "The rod may be close along the brick or stone, it makes no difference. There will be no need of rod on each side of the building, but let the cast iron hoop and the others you speak of be connected with the rod, and it will be in those places at least, as if there were rods on every side of the chimney.

"A three-fourth rod is no doubt better than a half-inch, and, except for * From the London Architect, for November, 1850.

†The very reverse of what was formerly held by high authorities.