« PreviousContinue »
Time, h. m. 2 44 % 45 2 46 2 47 2 48 2 49 2 50 2 51 2 52 2 53 2 54 2 55 2 56 2 57 2 58 2 59 3
243.00 247.75 251.25 255.25 259.75 264.00 268.37 273.00 277.00 282.00 286.37 291.00 295:37 300-00 304.25 308.75 313.00 317.00 322.10 326.12 331.00 335.62
boiler was raised from a pressure of 30 lbs. on the square inch to 80 lbs. in ten minutes. Mr. Fairbairn repeated these experiments to a still higher pressure with the following results, commencing at forty-four minutes past two o'clock:
a higher temperature than the above. In these experiments it will be observed that the pressure was raised from 11.75 lbs. on the sq. in. to 111.75 lbs. in twenty-two minutes; and on looking at the table it will be seen the pressure was accelerated in a greater ratio than the temperature. In the first experiments, for instance, the increase of pressure was about one pound for two degrees of heat; at a temperature of 277° it was as three to four; at 317°, the pressure increased about a pound for each degree; and at the end of the experiments, the proportions as four of heat to five of pressure. Mr. Fairbairn stated that he considered it more than probable, ihat had the instruments been calculated for higher temperatures and higher pressures, the point of explosion from 60 lbs. to 350 lbs. or 400 lbs. on the square inch would have been reached in twenty-eight minutes.
Those parts of a locomotive boiler comprised in the flat surfaces of the fire box were afterwards put to the test of experiment. Two thin boxes with flat surfaces, each 22 inches square and 3 inches deep, were constructed; one of them corresponding in the thickness of its plates (o-inch), distance of the stays, and in other particulars, with the sides of the fire box of the exploded boiler; and the other was formed of plates of the same thickness, but with the stays only four inches apart instead of five: The first box, therefore, containing sixteen squares of 25 inches area, represented the exploded boiler; the other, with twenty-five stays of 16 inches area, represented the new construction of boilers. When hydraulic pressure was applied to the first box, not the least swelling of the sides was perceptible till a pressure of 455 lbs. on the sq. in. had been put upon it, and then the swelling amounted to only .03 of an inch. At a pressure of 815 lbs. the box burst, by drawing the head of one of the stays through the copper, which, froin its ductility, offered less resistance to pressure in that part where the stay was inserted. The swelling of the sides the minute before bursting was •08 of an inch. In the next series of experiments with the box, in which the stays were placed closer together, the following results were obtained, showing the relative pressures and swellings of the sides up to 1595 lbs, on the square inch. At a pressure of 1625 lbs. the box burst, by one of the stays drawing through the plate, after sustaining the pressure upwards of a minute and a bali :
Pressure in lbs. Swelling in the Pressure in lbs. Swelling in the
per sq. in.
sides in ins.
485 575 635 755 965 1355 1385
The foregoing experiments Mr. Fairbairn considered to be conclusive as to the superior strength of the flat surfaces of a locomotive fire box, as compared with the top or even with the cylindrical part of the boiler. The enormous pressure sustained by the flat surfaces of a fire box when stayed in the manner now adopted, as exemplified in the second series of experiments, is greater than can possibly be attained in any other part of the boiler, however good the construction; in fact, there is no limit to the pressure that may be sustained if the stays be increased in thickness and in number.
In the discussion which ensued on the reading of this important paper, Mr. Samuelson observed, that as many flat marine boilers are now being constructed, it was desirable that the results of the foregoing experiments should be extensively known, as they would tend to remove the prejudice which had been so long entertained against the use of flat boilers.
In reply to a question, whether the heat requisite to get up a pressure of steam equal to the hydraulic pressure applied might not weaken the iron, Mr. Fairbairn stated, that the effect of beat on the strength of wrought iron was a subject he was about to investigate, but at present he could not give a definite answer. With respect to cast iron, he had determined that the strength increased up to a temperature of 300° Fahr., and at higher temperatures it became weakened.
Mr. Hopkinson said, that he understood experiments had been made with wrought iron in America, from which it appeared that the strength continued to increase to as high a temperature as 600°.
Experiments on the Effect of Re-Melling on the Strength of Iron.* Mr. Fairbairn presented a report of experiments undertaken at the request of the Association, “On the Mechanical Properties of Metals as derived from repeated Meltings, exhibiting the maximuin point of Strength and the Causes of Deterioration." In making the experiments, one ton of Eglinton hot-blast iron was operated on. The proportions of flux and coke at each re-melting were accurately measured, so as to be alike in each. The iron was run into bars 1 inch square, and the trials were made
* From the London Civil Engineer and Architect's Journal, October, 1853.
on lengths of about 4 feet, supported at each end, and the weight applied in the centre gradually, until the bar broke. One bar was reserved at each trial, and the rest of the iron was re-melied This succession of remeltings and trials was repeated seventeen times, when the quantity of iron was so much reduced, that it was not considered desirable to continue the experiments. The results obtained prove that cast iron increases in strength up to the twelfth melting, and that it then rapidly deteriorates. The commencing breaking weight was 403 lbs., and this went on increasing until at the tweltth melting the breaking weight was 725 lbs. At the thirteenth it was 671 lbs.; at the fifteenth, 391 lbs.; at the sixteenth, 363 lbs.; and at the seventeenth melting the bar broke with 330 lbs. After the fourteenth melting, the molecules of the metal, when fractured, appeared to have undergone a decided change. There was a bright band,
a like silver, on the edge of the bar, whilst the middle retained the ordinary crystalline fracture; and in the succeeding meltings the metal was bright all over, resembling the fracture of cast steel. Mr. Fairbairn exhibited specimens of the iron broken at each successive melting, and he said it was his intention to have them analyzed, to ascertain the chemical change that had been effected by the repeated processes.
On the Combined Steam and Ether Engine.* Mr. G. Rennie made a communication “On the Combined Steam and Ether Engine,” a French invention applied to propel a ship from Marseilles to Algiers, which he had lately examined. Mr. Rennie bad been requested to investigate the working power of this engine, and, accompanied by his son, he made a voyage in the vessel from Marseilles to Algiers and back. The engine was originally intended to be worked by steam, and the boiler is adapted to an engine of 30 horse power. The principle of the construction as it is now worked is this: The heat given out by the steain in condensing is applied to boil ether; the vapor thus generated is admitted into a distinct cylinder, and the work it does is so much gained from the waste heat of the steam. The condenser is sursounded by tubes containing the ether, which thus aids in condensing the steam; and as ether boils at a temperature of 100° Fahr., there is a tolerably efficient condensation of steam produced by the temperature at which the ether boils. The ether, after having done its work in its separate cylinder, is condensed in a refrigerator surrounded by cold water, and it is then again in a state to act as a condenser of the steam. The loss of either vapor by leakage during this repeated vaporization and condensation, amounts in value to one franc per hour. Special arrangements are made for dissipating the vapor that escapes, so as to prevent ignition, and with that provision Mr. Rennie considers there is no danger. In the return voyage, Mr. Rennie placed the coal under lock and key, and superintended the delivery of it, so that no deception might be practised, and he estimates the saving of fuel from this combination of ether with steam at nearly 70 per ct. It had been estimated by a French commission at 74 per cent. The French government have paid the inventor, M. Dutromblet, a large sum for the invention, and are about to put it in operation in a ship of 1500 tons burthen, with engines of 150
• From the London Civil Engineer and Architect's Journal, October, 1853.
horse power, which will have the advantage of the experience gained during the working of the present engine.
Mr. Taylor, Jr., the son of the engineer who constructed the engine of the Marseilles boat, said that there were many defects in the present arrangement, which would be remedied in the engines about to be made. The condensers are at present very imperfect, and do not expose a sufficient surface.
Mr. Sykes Ward said, that good ether does not corrode metals; therefore, there could be no objection to the employment of it on that account. The attempts that had previously been made to apply spirituous vapor as a motive power necessarily failed; because though alcohol and ether boil at a much lower temperature than water, their vapors are nuch heavier, and carry off as much heat at a given pressure, when applied, as steam.
Mr. Fairbairn stated, that in the best Lancashire steam engines, when working expansively, 24 lbs. of coal per horse power is the quantity consumed, which was nearly equal to the quantity consumed during the voyage from Algiers to Marseilles—whilst some of the steamboats on the Humber burn 10 lbs. of coal per horse power; therefore, compared with that wasteful expenditure of fuel, the steam and ether engiue presented great advantages.
Other members spoke encouragingly of the combined power, though the condensation of the steam it was considered must be imperfect, as the vacuum is not good at a temperature higher than 90°.
French System of Iron Floors.* These floors are composed of joists, slightly arched in the proportion of 0.005 metre in the metre; they are placed at the distance of 1.00 metre froin centre to centre, and are united by entretoises, or flat bars of iron, at the same distance apart. These entretoises rest on the lower projecting edges of the joists, and are secured in that position by passing into, and being fastened to, a band round the joists.
On the entretoises are tied (by means of wire) square iron rods, the same length as the joists.
Certain joists have ends fitted to act specially as ties, as have also the entretoises; thus the whole being firmly built into the walls, the sides of the houses are effectually united. The iron work is then painted, and afterwards filled with pottery bedded in plaster, or with plaster alone, by which process a ceiling is formed to the apartment below; this portion of the work is done as soon as the walls are of sufficient height to receive it.
Where a wooden floor is required, it is nailed to small joists notched in between the iron work.
The joists are of rolled iron, regulated in their size and depth by their span; the other portions are made in a manner to insure their going together without the aid of forge or file at the place of construction.
The whole, complete, forms a floor at once light and fire proof, occupying about 15 per cent. less space, and adding (in Paris) little to the ordinary cost of wooden construction.
The accompanying drawing is for a span of from 5:00 to 6.00 metres, upon the system of Mr. Thuasne.
H. H. B. * From the London Builder, No. 539.