(figs. 1, 2, and 3) 33 feet long, 5 feet 6 inches diameter, with two round flues 19 inches diameter through the centre; this boiler had 40 feet of heating surface to the nominal horse-power of the engine: the two flues contained 20 feet, and the shell 20 feet per nominal horse-power; the furnace was below the boiler at the fore-end, had a fire-grate of 26 square feet; the fire passed underneath the boiler to the opposite end from the furnace, and returned along the sides, and then passed back again through the flues to the chimney. The temperature above the centre of the fire was found to be, upon one occasion, 3200°; at the top of the bridge 1730'; the temperature of the gases Fig. 1. Fig. 2. gradually reduced as they passed back the remaining length of 26 feet under the boiler and along the side flues, till they entered the centre flues at 1163°, and left them at about 800°. Thus the furnace containing a surface of 2 feet per nominal horse-power reduced the heat about 1500°; the shell of the boiler behind the furnace, of about 18 feet per nominal horse-power, reduced the temperature about 600°; and the flues containing a surface of 20 feet per nominal horse-power red uced the temperature about 350°. The temperatures of the gases in the flues were found to be about the same in the centre as at the top; but at the bottom of the flue the tempe ratures of the gases were at the fore-end rather less than at the top, but towards the Fig. 4. Fig. 5. 1076 back end the temperature of the bottom of the flues reduced gradually below the temperature at the top to the extent of 300°. Upon another occasion the temperature over the centre of the fire was found to be 3610°; at the top of the bridge 1739°; and the different temperatures of the flues were as indicated in fig. 1, where the average temperatures of the flues at B'= $26°, B2= 879°, B' 937°, B' = 959°, and at B' 9910. The temperatures at the top of the flues at C3982, at C' = 1034°, at C1037. The temperatures at the bottom of the flues at A1= 571°, A2 = 603°, A3=678°, A=764°, A5 = 822°. It would therefore appear that, notwithstanding the large amount of surface in this boiler, the evaporative power is very inferior, as = = Fig. 6. the amount of heat taken out of the gases per square foot of heating surface is very small; and that the natural conclusion is that the gases pass along in straight lines, and only the thin stratum in contact with the surface is cooled down. In the results of the spiral boiler (fig. 6) three times the quantity of heating surface was found to reduce six times the quantity of gas from the same temperature of 3200°, to a temperature of 4800 instead of 800°, showing that a more complete turning over of the gases is much wanted in our land boilers. The water evaporated per hour in the land boiler referred to was found by meter to be 2000 lbs., and the coal, best Glasgow quality, found to be 300 lbs. per hour; making about 6 lbs. of water per pound of coal. During the measuring of the water evaporated by the meter, indicator diagrams of the engine were taken with a view to calculate the weights of steam by the ordinary method, and the calculations were found to agree with the meter; these calculations can be repeated and substantiated at any time. The second type of boiler tested was that of the ordinary steam-boat horizontal tubular boiler (fig. 4); the example chosen was one in a first-class ocean steamer; the temperature of the furnace was found to be 3200°, and the inside of the funnel about 1100°. The heating surface of this boiler was 22 feet per nominal horse-power, and the water evaporated about 8 lbs. per pound of coal, according to the calculation from the diagrams. The coal consumed was about 20 lbs. per square foot of fire-grate, of the best Glasgow coal. The next example taken was that of a first-class vertical tubular boiler (fig. 5), on Mr. David Napier's principle, now universally selected on the Clyde for river steamers. This boiler had a surface of about 22 feet per nominal horse-power; the temperature of the fire was found to be about 3300°, and in the funnel 1160°; 480 入 the weight of water evaporated was found by calculation to be 8 lbs. per pound of coal consumed, and the weight of combustion about twenty pounds square foot of fire-grate. In the spiral boiler (fig. 6) of the 'San Carlos,' Guayaquil,' and 'Prinz van Orange' the boilers were found to give the following peculiar results:-first, that even with Scotch coal there was no smoke emitted from the chimney, and no carelessness on the part of the fireman seemed to occasion the formation of smoke; second, that the boilers showed a bright furnace, indicating first-class draught; the temperature of the funnel was found to be 480°, whilst the fire was at its greatest. energy. The heating surface was, in the case of the San Carlos' and 'Guayaquil,' 2200 square feet, the coal consumed 1400 lbs. per hour, and the water evaporated 11 lbs. per pound of coal consumed; the fire-grate contained about 76 square feet, and the rate of combustion about twenty pounds per square foot of fire-grate. The heating surface of the boiler was 18 feet per nominal horse-power; the coal consumed was Glasgow best steam coal. The stoke-hole was found to be remarkably cool, and the boiler, which was loaded to 52 lbs. on the square inch steam pressure, and tested to 150 lbs. on the square inch water pressure, was found to be perfectly tight. In the case of the 'San Carlos,' I may mention that that ship has now steamed about 20,000 miles, and the vessel has not been in any one port more than three days; during that time she has been consuming soft Chili coal for a considerable part of her voyage, and the merits of the long flue show a decided advantage in this boiler over the ordinary tubular boiler for the native bituminous coal of South America. In order to give a more extended form of the comparative evaporative power of various flues and tubular boilers, the writer begs to lay before this Association the accompanying Table. It shows several proportions of heating surface and evaporative powers of several ships that have come under his notice. He can certify the accuracy of most of these particulars, except that shown in the last column, which is taken from Professor Rankine's report on the performance of the 'Thetis.' This vessel has about six times more heating surface in her boilers in proportion to the coal consumed, than any example the writer is aware of. The boiler is Craddock's patent boiler, though that inventor's name appears rarely to be mentioned in con nexion with the said vessel. Efficient, however, as this boiler must be as an evaporator, it cannot possibly accomplish the quantity shown in this Table. The theoretical quantity of water capable of being heated from 90°, and evaporated at, say 2120, with an infinite quantity of heating surface and a perfect fire, is somewhere about 13 lbs. per pound of coal; whilst from the diagrams represented in Professor Rankine's report of the 'Thetis' performance, 18 lbs. weight appear to be about the quantity of water per pound of coal. This calculation I have made from the diagrams published, and any party interested may repeat the calculations. The calculation is made as follows: the area of the large cylinder, as shown in the diagram, is 1380 square inches, or 9.583 square feet. The four revolutions of piston marked on the diagram 491, 52, 53, and 52 revolutions per minute, with a stroke of 2 feet, or say 258 12 feet per minute, gives 258 12X9.583 × 60=146433 cubic feet per hour. And if we take the average pressure shown in the four diagrams at the end of the piston stroke, supposing the barometer to be 14.5 lbs., we find the weight of that steam to be about 44 cubic feet per pound: this number therefore, divided by 44, gives the quantity of steam as 3300 pounds per hour; to this must be added 2 for contents of ports and clearance, which makes 3465 pounds of steam. This clearly gives the weight of the steam per hour given out of the cylinders after the work is performed, to this therefore must be added the quantity of heat that must have disappeared during the performance of the work; this, in the case of the Thetis,' is about of the entire heat; we must therefore add, or say 3165+693=4158 pounds of water must have been raised from a temperature of about 100° and evaporated, or say 18 lbs. of water to the pound of coal said to be consumed; this result is about equal to 20 lbs of water evaporated at 212°, to the pound of coal consumed; a quantity quite absurd. Comparisons of certain Results obtained fram Certified Diagrams of Steamers 'Elk,' ' Earl of Aberdeen,'' Valparaiso,' 'Pride of Erin,' ' Inka,'' Europa,'' Cambrian,' and Thetis.' Area of Fire-grate...... Steam evaporated per Glasgow best. Newcastle. Welsh. Welsh. Welsh. Welsh. Welsh. 190ft. 130ft. 252 50 314 247 4300 2400 4100 480 7000 5400 About 4000 4480 226 Good. It therefore appears that in the report referred to, the indicated power of the said diagrams may be correct, but the coals said to be consumed per indicated horsepower per hour, namely 108, must be wrong; and before a proper comparison could be established between the merits of the 'Thetis'' boiler and that of any other boiler, a correct trial of the former would be necessary. In the mean time we have but to 1860. 14 consider that the report of Professor Rankine was based upon one hour's consumption of say 230 lbs. of coal, and compare that with a mass of boiler, water and firebrick, weighing 20 tons, at a temperature of say 300°, it is evident that the mass of heat in proportion to the coal consumed is so great, that no conclusion should be made from such an experiment; also, that when the quantity of coal said to be consumed, viz. 230 lbs., is compared with area of fire-grate, say 40 square feet, it is evident that the result should not be depended upon, as no ordinary comparisons could be made of the condition of the fires before and after the experiment. In conclusion, let me ask of every party present to consider the trial trips of steam-ships and boilers in their true lights, and before drawing any inferences from such short trials, make a perusal of results obtained from sea voyages. The evaporative power and economy of boilers is one of the most important subjects for this Society to consider. We need only refer to the able Report drawn up by the Steam Shipping Committee of the British Association, to show how mixed up the question of the relative efficiency of the boiler and engines is generally considered. Indeed the American navy returns form the only reports showing the evaporative power of the boilers in this list, and the whole merit of a good evaporating boiler is often sacrificed to the character of the engines. With regard to the 'Thetis,' I would recommend any mistake to be remedied as soon as possible, as there are many contracts, involving much responsibility, formed in consequence of this report, that will lead to serious loss and disappointment to the steam-shipping interest, and the engineering profession of this country. On the Density of Saturated Steam, and on the Law of Expansion of Superheated Steam. By WILLIAM FAIRBAIRN, LL.D., F.R.S. &c. This paper contained a continuation of the experiments detailed in a paper read by Mr. Fairbairn at the Aberdeen Meeting, and which had been carried on in conjunction with Mr. Tate. Experimental determinations had been obtained of the density of steam fully confirming the anticipations of Mr. Thomson and Mr. Rankine, that the vapour of water does not exactly obey the gaseous laws. They show that the density of saturated steam is always greater than that given by the gaseous laws, even for temperatures as low as 136° Fahr., and at pressures below that of the atmosphere. The experiments at present extend over a range of temperature from 136° Fahr. to 292°, or from 2-6 to 60 lbs. pressure per square inch. The general result obtained is expressed in the following formula, which closely agrees with the experiments, where v is the specific volume or ratio of the volume of the steam to that of the water which produced it, at the pressure P, expressed in inches of mercury. On the subject of superheating steam, the experiments throw some light, which the author hopes to follow up by a special series of experiments. They show that within a short distance of the maximum temperature of saturation the rate of expansion is variable, being higher than that of a perfect gas near the saturation point, and rapidly decreasing, till at a point at no great distance above the temperature of saturation it becomes sensibly identical with that of a perfect gas. On an Atmospheric Washing Machine. By JOHN Fisher. The action of this machine was derived from streams of air forced through the water from below. The author in his paper observed, that for effectual use the water must never be of a higher temperature than 140° of Fahrenheit. It was stated that machines on this principle, driven by steam-power, had been for some time past in successful operation for cleansing the soiled laces at Messrs. Fishers' manufactory at Nottingham. On Giffard's Injector for Feeding Boilers. By WILLIAM FROUDde. In this instrument a jet of steam taken from the boiler and issuing from a properly tapered orifice, is met by and enveloped in a regulated supply of water, either cold or of limited temperature. The column formed by the combination of water and steam is made to impinge on the aperture of a similarly tapered orifice, of rather smaller area, connected with the feed-pipe; and penetrating this orifice, it flows in a continuous stream into the boiler. The rationale seems to be as follows:-were it possible to condense such a jet of steam by a simple abstraction of temperature, it would collapse into a jet of water having onlyth of its previous sectional area, its particles, however, retaining the same weight and velocity, and therefore the same momentum for each unit of time which they had possessed as steam. And since the momentum of a jet is the exact dynamic equivalent of the pressure which produces it, this water-jet would possess a momentum equal to that of a jet of equal diameter taken from a boiler having 1700 times the pressure of that from which itself had issued as steam, and would be capable of penetrating a boiler having a pressure enlarged almost in the same proportion. In the injector the water which is added condenses the steam and becomes incorporated with it, forming a compound jet which possesses for each unit of time the same momentum which the jet of steam possessed. And if the supply of water be duly regulated, the sectional area of the compound jet may be precisely adapted to the orifice of the feed-pipe. Now were that orifice equal in area to the steam-jet orifice, and were a jet of water allowed to issue from it under the same pressure which discharged the steam, the water-jet would have the same momentum for each unit of time as the steam-jet had, and therefore as the compound jet derived from it; and the two would precisely neutralize one another when brought into opposition. If, however, the steam-jet orifice be the larger of the two, then the jet derived from it, if reduced by condensation to the diameter of the smaller, will be the stronger in the same proportion, since it will possess the momentum due to the larger area of pressure; it will therefore drive back the water which is striving to escape from the feed-pipe, and will pass as a continuous stream into the boiler. The water supply is considered to be correctly adjusted when the passage takes place without an overflow of steam or water; but the test is deceptive; for an overflow of steam merely implies that the supply of water is barely sufficient to condense the steam into a jet as small in section as the feed-pipe orifice; an overflow of water merely implies that though the steam is fully condensed, the supply of water has enlarged the compound jet to a section exceeding that of the feed-pipe orifice. In reality the operation should be brought as near as possible to the latter limit; for though it will indeed seem to be proceeding quietly and properly in all the intermediate stages, it will be found that the compound jet, when not so enlarged as to fill the feed-pipe orifice, possessing its full momentum in a smaller section, will have energy enough to take up with it and carry into the boiler a considerable quantity of air, wasting thus not only its own power, but in a high degree that of the engine also, when it is a condensing one, since it encumbers the air-pump with extra duty. On a Process for covering Submarine Wires with India-rubber The author exhibited a model of his machine, which effected the object by winding strips of rubber, and moistening the same with naphtha during the process of covering; the wire thus formed being covered with a thread of vulcanized Indiarubber, and the whole afterwards subjected to a temperature of 140°. The wires thus covered were protected with a plaited covering of hempen cord, into which longitudinal steel wires were introduced for the purpose of giving strength. Suggestions relative to Inland Navigation. The fact that the forces operating in canal and river navigation are so different |