it working, there being either excessive smoke from bituminous coal or reduced evaporative economy. In 1880 Mr. Howden designed an arrangement intended to overcome the defects of both the closed ash-pit and closed stoke-hold systems. An air-tight reservoir or chamber is placed on the front end of the boiler and surrounding the furnaces. This reservoir, which projects from 8 to 10 inches from the end of the boiler, receives the air under pressure, which is passed by the valves into the ash-pits and over the fires in proportions suited to the kind of fuel used and the rate of combustion required. The air nsed above the fires is admitted to a space between the outer and inner furnace-doors, the inner having perforations and an air-distributing box through which the air passes under pressure. By means of the balance of air-pressure above and below the fires all tendency for the fire to blow out at the furnace-door is removed. By regulating the admission of the air by the valves above and below the fires, the highest rate of combustion possible by the air-pressure used can be effected, and in same manner the rate of combustion can be reduced to far below that of natural draught, while complete and economical combustion at all rates is secured. A feature of the system is the combination of the heating of the air of combustion by the waste gases with the controlled and regulated admission of air to the furnaces. This arrangement is effected most conveniently by passing the hot fire-gases after they leave the boiler through stacks of vertical tubes enclosed in the uptake, their lower ends being immediately above the smoke-box doors. Installations on Howden's system have hitherto been arranged for a rate of combustion to give at full sea-power an average of from 18 to 22 I.H.P. per square foot of fire-grate with fire-bars from 5' 0" to 5' 6" in length. It is believed that with suitable arrangement of proportions even 30 I.H.P. per square foot can be obtained. For an account of recent uses of exhaust-fans for increasing draught, see paper by W. R. Roney, Trans. A. S. M. E., vol. xv, FUEL ECONOMIZERS. Green's Fuel Economizer.-Clark gives the following average results of comparative trials of three boilers at Wigan used with and without economizers: Coal per square foot of grate per hour...... Without 21.6 73.55 9.60 With Economizers. 21.4 79.32 10.56 Showing that in burning equal quantities of coal per hour the rapidity of evaporation is increased 9.3% and the efficiency of evaporation 10% by the addition of the economizer. The average temperatures of the gases and of the feed-water before and after passing the economizer were as follows: Taking averages of the two grates, to raise the temperature of the feedwater 100° the gases were cooled down 250°. Performance of a Green Economizer with a Smoky Coal. -The action of Green's Economizer was tested by M. W. Grosseteste for a period of three weeks. The apparatus consists of four ranges of vertical pipes, 6% feet high, 334 inches in diameter outside, nine pipes in each range, connected at top and bottom by horizontal pipes. The water enters all the tubes from below, and leaves them from above. The system of pipes is enveloped in a brick casing, into which the gaseous products of combustion are introduced from above, and which they leave from below. The pipes are cleared of soot externally by automatic scrapers. The capacity for water is 24 cubic feet, and the total external heating-surface is 290 square feet. The apparatus is placed in connection with a boiler having 355 square feet of surface. This apparatus had been at work for seven weeks continuously without having been cleaned, and had accumulated a 1⁄4-inch coating of soot and ash, when its performance, in the same condition, was observed for one week. During the second week it was cleaned twice every day; but during the third week, after having been cleaned on Monday morning, it was worked continuously without further cleaning. A smoke-making coal was used. The consumption was maintained sensibly constant from day to day. GREEN'S ECONOMIZER.-RESULTS OF EXPERIMENTS ON ITS EFFICIENCY AS AFFECTED BY THE STATE OF THE SURFACE. (W. Grosseteste.) It is apparent that there is a great advantage in cleaning the pipes daily -the elevation of temperature having been increased by it from 88° to 153°. In the third week, without cleaning, the elevation of temperature relapsed in three days to the level of the first week; even on the first day it was quickly reduced by as much as half the extent of relapse. By cleaning the pipes daily an increased elevation of temperature of 65° F., was obtained, whilst a gain of 6% was effected in the evaporative efficiency. INCRUSTATION AND CORROSION. Incrustation and Scale.-Incrustation (as distinguished from mere sediments due to dirty water, which are easily blown out, or gathered up, by means of sediment-collectors) is due to the presence of salts in the feed-water (carbonates and sulphates of lime and magnesia for the most part), which are precipitated when the water is heated, and form hard deposits upon the boiler-plates. (See Impurities in Water, p. 551, ante.) Where the quantity of these salts is not very large (12 grains per gallon, say) scale preventives may be found effective. The chemical preventives either form with the salts other salts soluble in hot water; or precipitate them in the form of soft mud, which does not adhere to the plates, and can be washed out from time to time. The selection of the chemical must depend upon the composition of the water, and it should be introduced regularly with the feed. EXAMPLES.-Sulphate-of-lime scale prevented by carbonate of soda: The sulphate of soda produced is soluble in water; and the carbonate of lime falls down in grains, does not adhere to the plates, and may therefore be blown out or gathered into sediment-collectors. The chemical reaction is: Sulphate of lime+Carbonate of soda = Sulphate of soda+Carbonate of lime Sodium phosphate will decompose the sulphates of lime and magnesia: Sulphate of lime + Sodium phosphate = Calcium phos. +Sulphate of soda. CaSO4 Na,HPO CaHPO4 Na,SO Na,SO Sul. of magnesia+Sodium phosphate Phosphate of magnesia+Sul.of soda. MgSO4 = MgHPO Where the quantity of salts is large, scale preventives are not of much use. Some other source of supply must be sought, or the bad water purified before it is allowed to enter the boilers. The damage done to boilers by unsuitable water is enormous. Pure water may be obtained by collecting rain, or condensing steam by means of surface condensers. The water thus obtained should be mixed with a little bad water, or treated with a little alkali, as undiluted, pure water corrodes iron; or, after each periodic cleaning, the bad may be used for a day or two to put a skin upon the plates. Carbonate of lime and magnesia may be precipitated either by heating the water or by mixing milk of lime (Porter Clark process) with it, the water being then filtered. Corrosion may be produced by the use of pure water, or by the presence of acids in the water, caused perhaps in the engine-cylinder by the action of high-pressure steam upon the grease, resulting in the production of fatty acids. Acid water may be neutralized by the addition of lime. Amount of Sediment which may collect in a 100-H.P. steam-boiler, evaporating 3000 lbs. of water per hour, the water containing different amounts of impurity in solution, provided that no water is blown off: Grains of solid impurities per U. S. gallon: Equivalent parts per 100,000: 8.57 17.14 34.28 51.42 68.56 85.71 102.85 120 137.1 154.3 171.4 Sediment deposited in 1 hour, pounds: .257 .514 1.028 1.542 2.056 2.571 In one day of 10 hours, pounds: 2.57 5.14 10.28 15.42 20.56 25.71 In one week of 6 days, pounds: 15.43 30.85 61.7 92.55 123.4 154.3 3.085 3.6 4.11 4.63 5.14 30.85 36.0 41.1 46.3 51.4 185.1 216.0 246.8 277.6 308.5 If a 100-H.P. boiler has 1200 sq. ft. heating-surface, one week's running without blowing off, with water containing 100 grains of solid matter per gallon in solution, would make a scale nearly .02 in. thick, if evenly deposited all over the heating-surface, assuming the scale to have a sp. gr. of 2.5= 156 lbs. per cu. ft.; .02 X 1200 × 156 × 1/12 = 312 lbs. Boller-scale Compounds.-The Bavarian Steam-boiler Inspection Assn. in 1885 reported as follows: Generally the unusual substances in water can be retained in soluble form or precipitated as mud by adding caustic soda or lime. This is especially desirable when the boilers have small interior spaces. It is necessary to have a chemical analysis of the water in order to fully determine the kind and quantity of the preparation to be used for the above purpose. All secret compounds for removing boiler-scale should be avoided. (A list of 27 such compounds manufactured and sold by German firms is then given which have been analyzed by the association.) Such secret preparations are either nonsensical or fraudulent, or contain either one of the two substances recommended by the association for removing scale, generally soda, which is colored to conceal its presence, and sometimes adulterated with useless or even injurious matter. These additions as well as giving the compound some strange, fanciful name, are meant simply to deceive the boiler owner and conceal from him the fact that he is buying colored soda or similar substances, for which he is paying an exorbitant price. The Chicago, Milwaukee & St. P. R. R. uses for the prevention of scale in locomotive-boilers an alkaline compound consisting of 3750 gals. of water, 2600 lbs. of 70% caustic soda, and 1600 lbs. of 58% soda-ash (Eng. News, Dec. 5, 1891). Mr. H. E. Smith, chemist of the Ry. Co., writes May, 1902, that this compound was abandoned several years ago and commercial soda-ash, known as 58° soda," containing about 97% pure carbonate of soda, substituted in the water in the locomotive tender tanks, where it dissolves and passes to the boiler. Its action is to precipitate a portion of the scale forming solids in a flocculent form so that they are kept loose and free from the metal until they can be blown or washed out. The amounts used vary according to the character of the water and are based on the following rules: For calcium and magnesium sulphates and chlorides, use soda-ash equal to the chemical equivalent of those com. pounds present. For calcium and magnesium carbonates, the amount of soda-ash to be used varies from nothing when sulphates or chlorides are high, up to about one fifth the equivalent of the carbonates, when sulphates and chlorides are low or absent. A few waters contain carbonate of soda originally, and for these less soda-ash or none at all is necessary. It may also be necessary to make some reduction in the dose of soda-ash when large amounts of other alkali salts are present. In any case it is not desirable to use more than 2 lbs. of soda-ash per 1000 gallons of water, or more than 10 lbs. per 100 miles of locomotive run, on account of the foaming produced. The above rule assumes that the boilers are fairly clean and are kept fairly free from sludge by blowing and washing out. On the C., M. & St. P. Ry. boilers are usually washed once in 500 to 2000 miles run, according to the character of the waters used. In the upper Mississippi valley the majority of the waters are below 20 or 25 grains of incrusting solids per gallon, and the greater portion of this is carbonates. For these the above treatment is very successful. From 25 to 50 grains, increasing difficulty is encountered on account of foaming produced by the large amounts of sludge and alkali, and above 50 grains, sodaash alone fails to keep the boilers clean in practical service. Kerosene and other Petroleum Oils; Foaming.-Kerosene has recently been highly recommended as a scale preventive. See paper by L. F. Lyne (Trans. A. Š. M. E., ix. 247). The Am. Mach., May 22, 1890, says: Kerosene used in moderate quantities will not make the boiler foam; it is recommended and used for loosening the scale and for preventing the formation of scale. The presence of oil in combination with other impurities increases the tendency of many boilers to foam, as the oil with the impurities impedes the free escape of steam from the water surface. The use of common oil not only tends to cause foaming, but is dangerous otherwise. The grease appears to combine with the impurities of the water, and when the boiler is at rest this compound sinks to the plates and clings to them in a loose, spongy mass, preventing the water from coming in contact with the plates, and thereby producing overheating, which may lead to an explosion. Foaming may also be caused by forcing the fire, or by taking the steam from a point over the furnace or where the ebullition is violent; the greasy and dirty state of new boilers is another good cause for foaming. Kerosene should be used at first in small quantities, the effect carefully noted, and the quantity increased if necessary for obtaining the desired results. R. C. Carpenter (Trans. A. S. M. E., vol. xi.) says: The boilers of the State Agricultural College at Lansing, Mich., were badly incrusted with a hard scale. It was fully three eighths of an inch thick in many places. The first application of the oil was made while the boilers were being but little used, by inserting a gallon of oil, filling with water, heating to the boiling-point and allowing the water to stand in the boiler two or three weeks before removal. By this method fully one half the scale was removed during the warm season and before the boilers were needed for heavy firing. The oil was then added in small quantities when the boiler was in actual use. For boilers 4 ft. in diam. and 12 ft. long the best results were obtained by the use of 2 qts. for each boiler per week, and for each boiler 5 ft. in diam. 3 qts. per week. The water used in the boilers has the following analysis: CaCO3, 206 parts in a million; MgCO3, 78 parts; Fe,CO,, 22 parts; traces of sulphates and chlorides of potash and soda. Total solids, 325 parts in 1,000,000. Tannate of Soda Compound.-T. T. Parker writes to Am. Mach.: Should you find kerosene not doing any good, try this recipe: 50 lbs. sal-soda, 35 lbs. japonica; put the ingredients in a 50-gal. barrel, fill half full of water, and run a steam hose into it until it dissolves and boils. Remove the hose, fill up with water, and allow to settle. Use one quart per day of ten hours for a 40-H. P. boiler, and, if possible, introduce it as you do cylinder- oil to your engine. Barr recommends tannate of soda as a remedy for scale composed of sulphate and carbonate of lime. As the japonica yields the tannic acid, I think the resultant equivalent to the tannate of soda. Petroleum Oils heavier than kerosene have been used with good results. Crude oil should never be used. The more volatile oils it contains make explosive gases, and its tarry constituents are apt to form a spongy incrustation. Removal of Hard Scale.-When boilers are coated with a hard scale difficult to remove the addition of 14 lb. caustic soda per horse-power, and steaming for some hours, according to the thickness of the scale, just before cleaning, will greatly facilitate that operation, rendering the scale soft and loose. This should be done, if possible, when the boilers are not otherwise in use. (Steam) Corrosion in Marine Boilers. (Proc. Inst. M. E., Aug. 1884).-The investigations of the Committee on Boilers served to show that the internal corrosion of boilers is greatly due to the combined action of air and seawater when under steam, and when not under steam to the combined action of air and moisture upon the unprotected surfaces of the metal. There are other deleterious influences at work, such as the corrosive action of fatty acids, the galvanic action of copper and brass, and the inequalities of temperature; these latter, however, are considered to be of minor importance. Of the several methods recommended for protecting the internal surfaces of boilers, the three found most effectual are: First, the formation of a thin layer of hard scale, deposited by working the boiler with sea-water; second, the coating of the surfaces with a thin wash of Portland cement particularly wherever there are signs of decay; third, the use of zinc slabs suspended in the water and steam spaces. As to general treatment for the preservation of boilers in store or when laid up in the reserve, either of the two following methods is adopted, as may be found most suitable in particular cases. First, the boilers are dried as much as possible by airing-stoves, after which 2 to 3 cwt. of quicklime, according to the size of the boiler, is placed on suitable trays at the bottom of the boiler and on the tubes. The boiler is then closed and made as air-tight as possible. Periodical inspection is made every six months, when if the lime be found slacked it is renewed. Second, the other method is to fill the boilers up with sea or fresh water, having added soda to it in the proportion of 1 lb. of soda to every 100 or 120 lbs. of water. The sufficiency of the saturation can be tested by introducing a piece of clean new iron and leaving it in the boiler for ten or twelve hours; if it shows signs of rusting, more soda should be added. It is essential that the boilers be entirely filled, to the complete exclusion of air. Great care is taken to prevent sudden changes of temperature in boilers. Directions are given that steam shall not be raised rapidly, and that care shall be taken to prevent a rush of cold air through the tubes by too suddenly opening the smoke-box doors. The practice of emptying boilers by blowing out is also prohibited, except in cases of extreme urgency. As a rule the water is allowed to remain until it becomes cool before the boilers are emptied. Mineral oil has for many years been exclusively used for internal lubrication of engines, with the view of avoiding the effects of fatty acid, as this oil does not readily decompose and possesses no acid properties. Of all the preservative methods adopted in the British service, the use of zinc properly distributed and fixed has been found the most effectual in saving the iron and steel surfaces from corrosion, and also in neutralizing by its own deterioration the hurtful influences met with in water as ordinarily supplied to boilers. The zinc slabs now used in the navy boilers are 12 in. long, 6 in. wide, and 1⁄2 inch thick; this size being found convenient for general application. The amount of zinc used in new boilers at present is one slab of the above size for every 20 I.H.P., or about one square foot of zinc surface to two square feet of grate surface. Rolled zinc is found the most suitable for the purpose. To make the zinc properly efficient as a protector especial care must be taken to insure perfect metallic contact between the slabs and the stays or plates to which they are attached. The slabs should be placed in such positions that all the surfaces in the boiler shall be protected. Each slab should be periodically examined to see that its connection remains perfect, and to renew any that may have decayed; this examination is usually made at intervals not exceeding three months. Under ordinary circumstances of working these zinc slabs may be expected to last in fit condition from sixty to ninety days, immersed in hot sea-water; but in new boilers they at first decay more rapidly. The slabs are generally secured by means of iron straps 2 in. wide and 3% inch thick, and long enough to reach the nearest stay, to which the strap is firmly attached by screw-bolts. To promote the proper care of boilers when not in use the following order has been issued to the French Navy by the Government: On board all ships in the reserve, as well as those which are laid up, the boilers will be completely filled with fresh water. In the case of large boilers with large tubes there will be added to the water a certain amounts of milk of lime, or a solution of soda may be used instead. In the case of tubulous boilers with small tubes milk of lime or soda may be added, but the solution will not be |