Maxims and Instructions for the Boiler Room / Useful to Engineers, Firemen & Mechanics; Relating to Steam Generators, Pumps, Appliances, Steam Heating, Practical Plumbing, etc.

CORROSION AND INCRUSTATION OF STEAM BOILERS.

No more perplexing question presents itself to the engineer and steam user than the one to be inferred from the above heading. Enormous losses of money, danger to life and property and the loss of position and the reputation of the engineer are involved in it. How to avoid these actual evils is of the first importance in steam economy. The subject at first sight seems to the average student a difficult one to master, but like all other matters pertaining to mechanics, investigation that is backed with reason, will show that much that appears obscure is really very plain indeed; this is because nature, even down to the sediment remaining in a boiler after the conversion of water into steam, operates in its formation with infinite exactness and along well known lines.

Boilers corrode on the outside as well as within, and to a great extent unless carefully cleaned and painted; but it is the damage caused by “hard” and acidulated water within the boiler that is to be principally guarded against.

An extreme example of incrustation has been described in that of a locomotive type of a stationary boiler. Its dimensions were: seventy-two inches in diameter, twenty-two feet long, with 153 three-inch tubes; shell, three-eighths; head, three-eighths, and made of iron. The scale against the back head was nearly two inches thick and completely filled the space between the tubes, so that circulation was impossible, the only wonder being that the boiler did not give out sooner than it finally did. The scale was even with the top row of tubes, the only part of the boiler generating steam being the fire box and the upper row of tubes, the others acting simply as smoke conduits. There was certainly a great loss of fuel, quite fifty per cent. Had it been a horizontal boiler it would have burned out before the scale became so heavy.

In the above instance, the loss in fuel is estimated at one-half. Careful experiment has proved an average loss of fuel as follows:

¹⁄₁₆ inch of scale causes a loss of 13 per cent. of fuel.
¹⁄₄ inch of scale causes a loss of 38 per cent. of fuel.
¹⁄₂ inch of scale causes a loss of 60 per cent. of fuel.

It must be remembered that dry steam, as it is used through the engine or for other purposes, carries away none of the impurities which pass with the water into the boiler; hence, in a battery of boilers burning, say, 20 tons of coal per day and evaporating 10 lbs. of water to a pound of coal, there is a body of water going through them every day of 200 tons. Multiply this by 300 days for a year = 60,000 tons, and it will be seen how very great is the problem of keeping the interior of the boilers free from scale and deposit.

Chemically pure water is that which has no impurities, and may be described as colorless, tasteless, without smell, transparent, and in a very slight degree compressible, and, were a quantity evaporated from a perfectly clean vessel, there would be no solid matter remaining.

But, strangely, investigation has proved that water of this purity rapidly corrodes iron, and attacks even pure iron and steel more readily than “hard” water does, and sometimes gives a great deal of trouble where the metal is not homogeneous. Marine boilers would be rapidly ruined by pure distilled water if not previously “scaled” about ¹⁄₃₂ of an inch.

Water is formed by the union of two gases—oxygen and hydrogen. These two are simple bodies, formed by the Creator in the beginning, which are found in combination in thousands of different forms. Both when alone are invisible. Take one volume of oxygen and mix it with two volumes of hydrogen and they will chemically unite and form water. This is by measure. By weight water is composed of 88.9 of oxygen to 11.1 of hydrogen = 100 parts. See pages 229, 230 for further information.

It is an important point to remember that when water is expanded about 1,700 times into steam, it is simply expanded water, as ice is hardened water, i.e., in expanding into steam the two constituent gases do not separate. Hence, in dealing with the impurities inside the boiler, it is to be observed that in no sense do they change the essential nature of water itself. The impurities are simply foreign bodies, which have no legitimate place in the boiler, and are to be expelled as dangerous foes. As a general principle, it may be stated that it is more profitable to soften and filter the water used in boilers than to trust to blowing out or dissolving the sediment and scale that will be otherwise formed, for observations show that “anti-incrustators” containing organic matter help rather than hinder incrustations, and are therefore to be avoided. For the remedy of foul water there are numerous contrivances to prevent it from entering the boiler, which is far better than trying to extract the sediment after it is there, though there are many ingenious methods for doing that also, some of which will be detailed hereafter.

PRELIMINARY PRECIPITATION OF WATER.

A good method of avoiding incrustations in steam boilers is evidently a preliminary purification of the feed-water, provided it can be done by means sufficiently simple. This is a problem which it is claimed has been solved by M. Dehne of Halle, by means of an arrangement which we will herewith describe. The fresh water, which is taken up by a feed pump, is sent into a heater where it is raised to a temperature that will be favorable to chemical reaction. It then passes into a mixer where it encounters certain reacting agents which have been pumped in there by a pump of special design. These reacting agents are composed of a mixture of carbonate of soda and of caustic soda, the carbonate of soda serving to precipitate the sulphate of lime contained in the feed water, while the caustic soda precipitates the carbonate of lime and the magnesia. The relative dimensions between the special pump and the feed pump are calculated in such a way that the proportions of carbonate of soda and caustic soda in the mixture have always a certain relation to the amount of lime and magnesia to be precipitated. The water of the mixture is frequently very much disturbed by the precipitations which are formed, and passes into a filter where all the matters that are held in suspension are retained. It then goes into the boiler. In cases where the feed-water is taken from a tank, the heater, the mixer, and filter are put in the suction pipe of the feed pump, but if, as often happens, the water is already under pressure and will pass directly through the three, the feed pump will take the water directly from the filter and pump it directly into the boiler.

A PRECIPITATOR FOR SEA WATER.

It is quite possible to prepare sea water in such a way as to practically prevent any serious deposit forming from it.

The process employed is to add to the sea water a known quantity of precipitator powder consisting chiefly of soda ash, and having done this in a closed vessel, to heat the mixture by blowing into it waste steam, until a pressure of from 5lbs. to 10lbs. is created; under these circumstances practically all the magnesium and calcium salts separate from the water and are easily got rid of by filtering it under pressure into the hot-well.

A precipitator 6 ft. 4 in. high and 3 ft. in diameter, holds a ton of water, and the time taken, from the first running the sea water in, to its delivery into the hot-well, need not exceed 1 hour and 15 minutes, so that in practice, giving plenty of time between the makes, it would be perfectly easy to prepare 8 to 12 tons in the 24 hours with a small precipitator of the size named. The prepared water has a density of ^l⁄₃₂nd, and may with safety be evaporated until its density is ⁵⁄₃₂nds, the salts present not crystalizing out until a density of from ⁶⁄₃₂nds to ⁷⁄₃₂nds is reached.

In preparing sea water in the way proposed, every precaution must be taken to add slightly less of the precipitant than is necessary to entirely throw down the calcium and magnesium salts, as it is manifestly impossible in practice to guard against small quantities of sea water finding way into the boiler either from leaky condensers or else being fed in by the engineer during some emergency, and if under these conditions any excess of the precipitant were present in the boiler, a bulky precipitate would be thrown down and cause trouble, although it would not bind into a solid scale.

Briefly recapitulated the means which are best adapted for preventing the formation of the dangerous organic and oily deposits considered are:

I. Filtration of condensed water through a coke column.

II. Free use of the scum cocks.

III. The use of water of considerable density rather than of fresh water.

IV. The use of pure mineral oil lubricants in the smallest possible quantity.

SCALE DEPOSITED IN MARINE BOILERS.

The analysis given below may be looked upon as typical of the incrustation formed by fresh water, brackish water and sea water respectively in marine boilers:

From this it is evident we may look upon the incrustation from fresh water as consisting of impure calcic carbonate, whilst that from sea water is impure calcic sulphate, the brackish water from the mouths of rivers yielding, as might be expected, an incrustation in which both these compounds are present in nearly equal quantities.

The importance of these differences in the deposit formed is very great, as it enables the shipowner to arrive at the conclusion as to the treatment that the boilers have received during the voyage, by examination and analysis of the scale that those boilers contain. Taking, for instance, the case of a ship which uses fresh water both for filling and make up, it is manifest that on her return to port the scale should be very slight and should consist mainly of calcic carbonate, whilst if the scale exceeds ¹⁄₁₆ in., and shows a preponderance of calcic sulphate, it is manifest that such scale could only have been formed by sea water, either leaking in from faulty condensers or being deliberately fed into the boilers.

With the introduction of high pressure steam a new and dangerous form of deposit has added to the trouble of the marine engineer; having entered the boiler, the minute globules of oil, if in great quantity, coalesce to form an oily scum on the surface of the water, or if present in smaller quantities, remain as separate drops; but show no tendency to sink, as they are lighter than water.

Slowly, however, they come in contact with small particles of other solids separating from the water and sticking to them, they gradually coat the particles with a covering of oil, which in time enables the particles to cling together or to the surfaces which they come in contact with. These solid particles of calcic carbonate, calcic sulphate, etc., are heavier than the water, and, as the oil becomes more and more loaded with them, a point is reached at which they have the same specific gravity as the water, and then the particles rise and fall with the convection currents which are going on in the water, and stick to any surface with which they come in contact, in this way depositing themselves, not as in common boiler incrustation, where they are chiefly on the upper surfaces, but quite as much on the under sides of the tubes as on top.

The deposit so formed is a wonderful non-conductor of heat, and also from its oily surface tends to prevent intimate contact between itself and the water. On the crown of the furnaces this soon leads to overheating of the plates, and the deposit begins to decompose by heat, the lower layer in contact with the hot plates giving off various gases which blow the greasy layer, ordinarily only ¹⁄₆₄ inch in thickness, up to a spongy leathery mass often ¹⁄₃ inch thick, which, because of its porosity is an even better non-conductor of heat than before, and the plate becomes heated to redness.

When water attains a temperature, as it does under increasing pressure, ranging from 175° to about 420° Fahr., all carbonates, sulphates and chlorides are deposited in the following order:
First. Carbonate of lime at 176° and 248° Fahr.
Second. Sulphate of lime at 248° and 420°.
Third. Magnesia, or chlorides of magnesium, at 324° and 364°.

It is to take advantage of this fact that mechanically arranged jets, sprinklers and long perforated pipes are introduced into the interior of the boiler; these tend to scatter the depositing impurities and also to bring the feed water more quickly to the highest heat possible.

With regard to the oxide of iron or iron salts in solution, these can best be treated with small quantities of lime. By adding re-agents, they set up chemical changes, which result in precipitation, which give the water a milky appearance; they divide into particles, and ultimately settle, leaving the water pure and bright. The mechanical treatment on a limited scale would be easy, a settling tank sufficing; but this becomes a different matter when large quantities have to be dealt with.

ANALYSIS OF AVERAGE BOILER SCALE.

The percentage only of each ingredient the scale is composed of is given, as it cannot be told how much water was evaporated to leave this amount of solid matter.

A LOCOMOTIVE-BOILER COMPOUND.

The lines of a certain great R. R. traverse a country where the water is very hard and they are compelled to resort to some method of precipitating the lime that is held in solution. After many tests and experiments they have made a compound and use it as follows: in a barrel of water of a capacity of fifty gallons they put 21 lbs. of carbonate of soda, or best white soda ash of commerce, and 35 lbs. of white caustic soda. The cost, per gallon, is about 2¹⁄₂ cents.

The compound is carried in this concentrated form, in calomine cans on the tender of each locomotive. A certain amount, according to the necessities of the case, is poured into the tender at the water tank at each filling. This amount is determined by analysis, and varies all the way from two to fifteen pints to two thousand gallons of water. The precipitating power of this compound may be taken roughly at ²⁄₃ of a pound of the carbonate of lime, or equivalent amount of other material, per pint of the compound. On their western lines where they are dealing with alkali waters and those containing sulphates, the company use merely 60 pounds of soda ash to a barrel of water. When the water is pumped into the boiler the heat completes the precipitation and aggregation of the particles, and this does away with all trouble of the tenders or injector tubes clogging up.

The case is an interesting one to stationary engineers, because where the water is pumped into the boiler from tanks the same compound can be used, provided the water contains the proper constituents to be precipitated by it; and where the water is taken from city water mains, it would be a simple matter to devise an apparatus to admit the compound to the feed pipes.

“Points” Relating to the Scaling of Steam Boilers.

The peculiarity about the sulphate of lime is that the colder the water the more of it will be held in solution. Water of ordinary temperature may hold as high as 7 per cent. of lime sulphate in solution, but when the temperature of the water is raised to the boiling point a portion of it is precipitated, leaving about .5 of one per cent. still in solution. Then as the temperature of the water is raised, still more of the substance is precipitated and this continues until a gauge pressure of 41 pounds has been reached which gives a temperature of about 200 degrees; at this point all the sulphate of lime has been precipitated. Many other scale forming substances act in a similar manner. This shows quite plainly that any temperature that can be produced by the use of exhaust steam would not be sufficient to cause the precipitation of all the substances which might be contained in the water.

That boiler incrustations are the immediate causes of the majority of steam boiler explosions is no longer a doubtable question.

Nearly all foreign matter held in solution in water, on first becoming separated by boiling, rises to the top in the form of what is commonly called scum, in which condition much of it may be removed by the surface blow-off. If not removed, however, the heavier particles will be attracted to each other until they have become sufficiently dense to fall to the bottom, where they will be deposited in the form of scale, covering the whole internal surface of the boiler below the water line, with a more or less perfect non-conductor of heat.

It is recorded that the engineer of the French ocean steamer St. Laurent omitted to remove a bar of zinc when repairing and cleaning out his boilers. On opening the boilers at the end of the voyage to his great surprise he found that the zinc had disappeared, but his boilers were entirely free from scale and the boiler plates not injured in the least.

It has been recently determined by some German experimenters that sugar effects a strong action upon boilers. It has an acid reaction upon the iron which dissolves it with a disengagement of hydrogen. The amount of damage done increases with the amount of sugar in the water. These results are worthy of note in sugar refineries and places where sugar sometimes finds its way into the boilers by means of the water supplied. The experimenters in question also find that zinc is strongly attacked by sugar; copper, tin, lead and aluminium are not attacked.

Two reasons, relating to incrustations, for not blowing out a boiler while under steam pressure may be given as follows: One is, that the foreign matter floating on top of the water will be deposited on the shell of the boiler as the water gradually subsides, and, second, the heated walls of the furnace will communicate a sufficiently high temperature to the boiler to dry and flake the sediment that would otherwise remain in the boiler in the shape of mud, which could easily be washed out were it not for the baking process.

Bark, such as is used by tanners, has an excellent effect on boiler incrustations. It may be used as follows: Throw into the tank or reservoir from which the boilers are fed a quantity of bark in the piece, in sufficient quantity to turn the water to a light brown color. Repeat this operation every month at least, using only half the quantity after the first month. Add a very small quantity of the muriate of ammonia, about one pound for every 2,000 gallons of water used. This will have the effect of softening as well as disintegrating the carbonate of lime and other impurities deposited by the action of evaporation.

Note.—Care must be exercised in keeping the bark, as it becomes broken up, from the pump valves and blow-off valves. This may be accomplished by throwing it into the reservoir confined in a sack.

Among the best samples of boiler compounds ever sent to the laboratory for analysis was found to be composed of:

This solution was formerly sold at a good round figure, but since its nature became more generally known, it is not found in market, but is largely used, consumers putting it up in lots sufficient to last a year or so at a time.

The above is strongly recommended by those who have used it, one pound of the mixture being added to each barrel of water used but after the scale is once thoroughly removed from the boiler, the use of sal soda alone is all that is necessary. By the use of ten pounds per week a boiler 26 feet long and 40 inches in diameter in one of the iron mills of New Albany, Ind., has been kept clean of scale equal to a new boiler.

There are other evils sometimes inherent in hard waters over and above the mere production of a crust. Some waters contain a great deal of soluble magnesia salts, together with common salt. When this is the case there is a great chance of corrosion, for the former is acted on by steam at high pressure in such a way that muriatic acid fumes are produced, which seriously corrodes the boiler, and, what is far worse, passes with the steam into the engine, and produces corrosion in the cylinders and other delicate fittings into contact with which the steam passes. All this can, however, be obviated by the removal of the magnesia from the water.

There has not been, and never can be, made a mechanical device which will precipitate all the ingredients contained in a water taken from a natural source of supply, and if it were possible to do so it would be the most ruinous thing one could do for the boilers, as water is the greatest solvent known to chemistry, and its nature is to hold in solution and be impregnated with the different elements it comes in contact with, to a certain per cent., and if its lime, magnesia, and the mineral salts are taken away, and the pure water is pumped into the boilers, it will take up the iron, causing pitting and grooving of the boilers. It is better to let nature take its course, to a certain extent, and neutralize what little mineral deposit forms in the boilers with as small an amount of vegetable matter as possible.

It is well to note that different waters require different treatment; what will be of benefit in one instance will be of no value whatever in a different water, many of the “compounds” sold to prevent and remove scale will certainly destroy a boiler if they are used persistently, because they are composed of the exact opposite chemicals which should be used; as an example it is stated that at one establishment one thousand dollars were expended annually for a mixture which it is said resulted in the reduction of the life and usefulness of the boilers of 50 per cent.

ENGINEERS’ TESTS

FOR IMPURITIES IN FEED WATER.

Much expense can be saved in fuel and boiler repairs by a little preliminary expenditure of money in securing a supply of good water for the steam boilers of a new establishment. Well water is nearly always inferior to the running water of streams; water from mines is especially hurtful, containing, as they do, large quantities of free sulphuric acid. Wells along the sea shore or on the banks of rivers affected by the tides, are likely to be saturated with chloride of magnesium. It is in determining these points that these ready tests of feed water are most useful.

A thorough and really scientific analysis of feed water is a costly and tedious process, but a simple and perhaps sufficiently accurate test may be made as follows: take a large (or tall) clear glass vessel and fill it with the water to be tested; add a few drops of water of ammonia, until the water is distinctly alkaline; next add a little phosphate of soda; the action of this is to change the lime, magnesia, etc., into phosphates, in which form they are deposited in the bottom of the glass. The amount of the matter thus collected gives a crude idea of the relative quality of sediment and scale-making material in the water.

Water turning blue litmus paper red, before boiling, contains an acid, and if the blue color can be restored by heating, the water contains carbonic acid. Litmus paper is sold by druggists.

If the water has a foul odor, giving a black precipitate with acetate of lead, it is sulphurous.

An experiment may be tried by dissolving common white or other pure soap in a glass of water, and then stirring into the glasses of water to be tested a few teaspoonsful of the solution; the matter which will be deposited will show the comparative amount of the scale-making material contained in the feed water.

In order to ascertain the proportion of soda to the feed water the following method is recommended:

1. Add ¹⁄₁₆th part of an ounce of the soda to a gallon of the feed water and boil it. 2. When the sediment thrown down by the boiling has settled to the bottom of the kettle, pour the clear water off, and 3, add ¹⁄₂ drachm of soda. Now, if the water remains clear, the soda, which was first put in, has removed the lime, but if it becomes muddy, the second addition of soda is necessary.

In this way a sufficiently accurate estimate of the quantity of soda required to eliminate the impurities of the feed water can be made and the due proportion added to the feed water.

By exercising a little judgment, the use of pure chemicals, with well cleaned vessels, test tubes, etc., the following reagents will determine the character of the most important elements which injure the iron surfaces of a steam boiler.

Carbonic acid is indicated by baryta water.
Sulphates are indicated by chloride of barium.
Chlorides are indicated by nitrate of silver.
Lime salts are indicated by oxalate of ammonia.
Organic matter is indicated by chloride of mercury.

The “base” of the better class of the various patented boiler compounds is tannin (whence tannic acid) and some form of alkali, and if the compounds were to be deprived of these two elements they would be absolutely worthless.

Where they contain, as some certainly do, sal-ammoniac, muriatic, hydrochloric and sulphuric acids, they cannot but act as boiler destroying agents.

Tannin or tannic acid is the principal ingredient used in preparing leather. It is found in a great variety of plants—sassafras root has it in large proportion, the gall nut and the bark of various trees, especially the oak produce it.

It is the presence of this acid that gives their only value to very many “compounds,” tan bark, gum catechu (which sometimes contains one-half part of tannic acid), etc. The acid seems to have but little effect where large quantities of sulphate of lime are present, but in waters where carbonate of lime predominates its detersive qualities are more marked.

The records of the Patent Office show that one boiler compound contains 23 per cent. of catechu, and others, 60, 81, 5, respectively, by which may be inferred the large quantity of this agent, which has been sold in combination with other chemicals, principally soda.

Note.

While the product of water steeped in clean tan bark may be favorable in its action upon boiler incrustation, it has been found to be very unsafe, in practice, to use the “tan liquor” taken from the vats. The danger arises from the fact that sometimes during the process of tanning leather, the required acidity cannot be produced by natural fermentation when sulphuric acid is added, in order to bring the liquor to its required strength—in due course, this corrosive substance acts injuriously on the boiler.

USE OF PETROLEUM OIL IN BOILERS.

The use of crude (unrefined) mineral oil in steam boilers is attended by risks caused by impurities and foreign substances mixed with it. These are likely to combine with the earthy matter in the water and tend to form instead of preventing scale; the tar and wax contained in crude petroleum combine with the sediment in steam boilers, and the paste prevents the water from reaching and protecting the plates. This is true particularly in shell boilers which have flat surfaces over the fire. Refined mineral oil has none of these disadvantages.

Kerosene oil has all the advantages to be derived from the use of crude petroleum and the above objections quite removed.

In one system of the application of steam the use of kerosene and petroleum cannot be recommended: that is when live steam is used for cooking purposes, the odor from the oil will impregnate the meat and other products designed for food consumption.

KEROSENE OIL IN BOILERS.

Under certain conditions, and with care and judgment, the use of refined petroleum has been found to be of great advantage in removing and preventing scaling in steam boilers.

There is no well authenticated case where a systematic, regular and uniform feed of pure kerosene oil to a steam boiler has failed to operate beneficially upon the scale formation.

The best results are obtained by the use of the oil under the same arrangement that cylinder oil is fed to an engine. The kerosene is sometimes introduced through a one-fourth inch branch to the suction pipe of the feed pump, leading to the vessel containing the oil, so that any quantity, large or small, can be put into the boiler simultaneously with the usual feed. The drawback to this arrangement is that when the feed water heater has to be cleaned, a gallon or more of the oil is often lost, which together with a very unpleasant odor, when used in this manner, tends to condemn its use. But when piped between the boiler and heater, these objections cease. We present an arrangement which is illustrated by cut on page 157.

This is nothing more than a storage system with sight feed, by use of which the oil can be fed drop by drop as desired—for each drop of water entering the reservoir a drop of oil is forced down the small ¹⁄₄-in. pipe, up the glass tube and on into the boiler.

In piping it is necessary to have the water or larger pipe (¹⁄₂ in.) attached through the lower plug as shown in cut, and the oil as shown, going through the smaller or ¹⁄₄-in. pipe—i.e., the oil pipe must, under all circumstances, be the smaller of the two.

In the figure is shown a piece of 6-in. gaspipe, about a foot in length, plugged at each end; the top plug has one opening, for an inch nipple “a” with top. This opening is to be used in filling the reservoir with oil. The bottom plug has two holes, one for the ¹⁄₂-inch water pipe, and the second for a small pet cock “B,” to let the water out, whenever it is necessary to refill the tank with kerosene. The water gauge connection is the ordinary, cheap brass fixture, with boxes, nipples, etc., used in boilers, with gasket of rubber bottom and top of the glass. The glass plainly exhibits the depth of water and oil in the reservoir as well as the feed of minute drops of oil as they speed on their beneficent mission softening the injurious scale. There are the usual 2 valves on the water glass; by opening the lower one more or less, the amount of oil used can be regulated to a nicety. The valves can be used to entirely cut off the apparatus at any time desired.

Note.—Should the end of the screw connection inside the holder which each one of these valves control, not be ¹⁄₄ inch, a reduced elbow should be used, as ¹⁄₄-in. pipe will give the best satisfaction when used as a stand pipe inside the reservoir.

The quantity of oil to be fed to a boiler is very largely to be determined by experiment commencing with a minimum and increasing the amount as found necessary to keep down the scale formation. The use of 2 qts. of the oil per week has been found to be sufficient for a boiler 4 feet in diameter and 12 feet long, and three quarts per week on boilers 5 feet in diameter. This quantity may be regarded as the smallest advisable to use and from that up to 1 to 2 gallons per diem in boilers, say of 125 horse power, when pushed to their capacity in evaporating water.

The result of careful experiments justifies the use of kerosene, the scale being less than in four years’ previous experience, and a large portion of the boiler showing the clean black steel, in as apparently good condition as when new.

Despite the small quantity of kerosene used in the boilers in this case, the odor was perceptible by opening an air valve to any steam radiator in any of the buildings. When as much as a gallon per week was used, the odor was very strong, but with one half that amount it was hardly perceptible, and only to be noticed when an air valve had been open a long time. And since commencing to use the oil a much greater deposit of rust scales than usual has been found in the various steam traps in the buildings, indicating that the oil is also exerting a cleansing influence on the pipes of the whole system.

Note.—Provision must be made for the removal of the scale as it drops from the internal surfaces of the boiler, as at times many bushels of it have been deposited directly over the furnace; hence, if a boiler is known to be badly incrusted, the kerosene should not be put in the first time more than three days before it is intended to wash the boiler.

Note 2.—The safety valve should be opened to allow the escape of the gas arising from the kerosene before cleaning out the boiler; where a lighted lamp or candle is used, as it must necessarily be—indeed this is a precaution which ought always to be observed in all cases, viz., properly to ventilate boilers, heaters, and tanks of all descriptions before entering them with lighted lamps and torches. While these gases are not likely to cause an explosion, they burn quite rapidly and should be promptly removed without giving opportunity for an accident.

The accumulation of gas is not confined to the use of kerosene oil for the prevention of scale in steam boilers, but is also found in flour mills, confectioners’, conduits for electric wires, brewers’ vats, etc. So, with common sense precautions, no extra risk is run in using kerosene oil in steam boilers.

MECHANICAL BOILER CLEANERS.

Owing to the fact (1) that nearly, if not quite all, the impurities which exist in feed water are set free by a high temperature attained under pressure; (2) that these impurities are left in the boiler by the constant use of the steam, there follows the result that the water remaining is more and more impregnated with the residuum composed of the foreign matters which (the water removed) constitutes mud, scale, etc.

The custom has been and is now to regularly “blow off” one or two gauges of this water once or twice per day replacing it with fresh water of less density; that this is a very imperfect method for removing the foreign matter is readily allowed, besides wasting absolutely all the units of heat contained in the water blown off.

Now, within the boiler while in use, under the operation of the fierce heat of the furnaces, are constant changes in the position of the water caused by the boiling, by the withdrawal of the steam and by the constant effort of the hot water to rise and the cold water to fall. The water thus keeps in circulation everything within the boiler, including the sediment, except in places where the water is from any cause without motion. In these quiet nooks there is a constant depositing of the elsewhere active foreign matters contained in the water, which deposits, in the form of mud and scale, left undisturbed, causes loss and danger.

It is in taking advantage of these facts, and of the principles of the circulation of hot and cold water, that mechanical boiler cleaners are brought into successful use.

These devices for the stilling of the water and collection of the sediment are made in various forms and all sizes and capacities, and are located at the sides or back of the boiler setting and even on top of the boiler. There is a system where pipes in a coil are fixed in the sides of the furnace and exposed to its greatest heat, and which, owing to their enlarged area, act as most efficient reservoirs. In all these devices there is an upflow pipe connected with the lower and coolest water, and a return pipe connecting with the top of the water where it is hottest. This arrangement assures a constant current which is more or less rapid according to the intensity of the fire and which keeps up as long as the firing is done. Where this current passes through the reservoir, the enlarged area and comparative quiet is favorable for the deposit of the sediment and in practical experience it does deposit nearly all of it. The collection of the impurities is helped by a funnel-shaped appliance placed at the opening of the upflow pipe, which, aided by the rapid flow of the hot water, carries the floating scum towards it into the reservoir. Attached to the reservoir is the blow-off pipe through which the deposited matter is removed as often as necessary.

The use of these mechanical cleaners is readily understood: (1) they provide a place of accumulation for the sediment; (2) they save the necessity of opening the boilers to remove by hand, the refuse of the boiler; (3) save fuel by avoiding the necessity of frequent blowing off one or two gauges of water, and (4) by the preventing the formation of scale with its attendant evils.

SCUMMING APPARATUS.

In addition to the bottom blow-out apparatus every boiler should be provided with means for blowing out water from the surface in order to remove the fine particles of foreign matter floating there, which afterward settle and consolidate as scale on the heating surfaces.