Chapter VI: Introduction (5)

_A general knowledge of the subject of steam engineering is the first requisite to success._ A few sample questions are here given to show the ordinary course pursued by examiners to determine the fitness of applicants:

How long have you been employed as an engineer, and where? Are you
a mechanic? Where did you learn your trade? Give some idea of the
extent of your experience as an engineer? What kind of boilers have
you had charge of? Describe a horizontal tubular boiler. Describe a
locomotive style boiler. Describe a vertical style boiler. Describe
a sectional water tube boiler. How thick is the iron in the shell
of your boiler? How thick should it be in the shell of your boiler?
How thick are the heads in your boiler? How thick should they be in
your boiler? How are the heads fastened to the shell? What is the
best way to put heads in a boiler? How is the shell riveted? What
size rivets are used? What distance apart are they? How should the
shell be riveted? Why do they double rivet some seams? What ones
are best double riveted? How is a horizontal boiler braced? How is
a locomotive boiler braced? What is the size of and forms of braces
generally used? What is the size of your boiler or boilers, length
and diameter? How many have you in charge? Name the horse power. How
many tubes are in the boiler? What size are they, and how thick? How
long are they? How are they secured? What is the difference between a
socket and a stay bolt? What is the tensile strength of Boiler Iron?
What is the tensile strength of Boiler Steel? What is mild steel?
What is CH No. 1 Iron? What is Flange Iron? What is Hot Short and
Cold Short Iron? What is the common dimensions of a Man Hole? What is
it for? What are Hand Holes for? Do you open them often? How often?
What are Crown Bars and where are they used? How is a Boiler Caulked?
What is a Drift Pin?

MECHANICAL STOKERS.

In the back counties of England for many generations before the steam engine was evolved from the brains of Trevithick, Watt and Stephenson, the word “stoke” was used, meaning to “stir the fire.” The word was derived from an ancient word, stoke, meaning a stick, stock or post.

To-day there are very many men who are called “stokers,” employed principally on locomotive engines, steam vessels, etc., and then there is the “stoke hole,” so-called, in which they do their work.

But, now comes the “mechanical stoker,” which is well named, as its office is to feed and “stir the fire” by a machine, thus relieving the fireman from much excessively hard toil and allowing the time and energy thus saved to be more profitably used elsewhere. The figure shows a view of the American Stoker which is a device of the most advanced type.

The principal parts of the machine are: 1, the Hopper, which may be filled either by hand shoveling or by elevating and conveying machinery; 2, the Conveyor Screw, which forces the coal, or indeed, any description of fuel, forward to the 3, Magazine, shown in the figure to the left; 4, a Driving Mechanism, which is a steam motor arranged conveniently in front of the hopper; 5, the Retort, so called from its being the place (above the conveyor) where the coal is distilled into gas.

NOTE.—An illustrated printed description of this machine is issued and sent free upon application by the makers. The American Stoker Co., Washington Life Building, Cor. Broadway and Liberty St., New York.

The rate of feeding coal is controlled by the speed of the motor, this being effected by the simple means of throttling the steam in the supply pipe to the motor. The shields covering the motor effectually protect the mechanism from dirt and dust. The motor has a simple reciprocating piston; its piston rod carries a crosshead, which, by means of suitable connecting links, operates a rocker arm having a pawl mechanism, which in turn actuates the ratchet wheel attached to the conveyor shaft. The stoker is thus entirely self-contained and complete in itself.

A screw conveyor or worm is located in the conveyor pipe and extends the entire length of the magazine. Immediately beneath the conveyor pipe is located the wind-box, having an opening beneath the hopper.

At this point is connected the piping for the air supply, furnished at low pressure by a volume blower. The other end of the wind-box opens into the air space between the magazine and outer casing. The upper edge of the magazine is surrounded by tuyeres, or air blocks, these being provided with openings for the discharge of air, inwardly and outwardly.

The stoker rests on the front and rear bearing bars; the space between the sides of the stoker and side walls is filled with iron plates, termed “dead grates.” Steam is carried to the motor by a 3/4-inch steam pipe. The exhaust steam from the motor is discharged into the ash pit.

In operation the coal is fed into the hopper, carried by the conveyor into the magazine, which it fills, “overflows” on both sides, and spreads upon the sides of the grates. The coal is fed slowly and continuously, and, approaching the fire in its upward course, it is slowly roasted and coked, and the gases released from it are taken up by the fresh air entering through the tuyeres, which explodes these gases and delivers the coal as coke on the grates above. The continuous feeding gives a breathing motion to this coke bed, thus keeping it open and free for the circulation of air.

It will be noted that in this machine the fuel is introduced from the bottom of the bed of fuel, technically speaking, upon the principle of “underfeeding.”

CHEMICAL TERMS

AND EXPLANATIONS RELATING TO FEED WATERS.

=_Chemistry_= is a science which investigates _the composition and properties of material substances_.

Nature is composed of elementary elements; knowledge of these bodies, of their mutual combinations, of the forces by which these combinations are brought about, and the laws in accordance with which these forces act, constitute chemistry, and the chemistry of steam engineering largely deals with the foreign bodies contained in the feed water of steam boilers.

=_Element._= In general, the word element is applied to any substance which has as yet never been decomposed into constituents or transmuted to any other substance, and which differs in some essential property from every other known body. The term simple or _undecomposed substance_ is often used synonymously with element.

There are about 70 _simple elements_, three-quarters of which are to be met with only in minute quantities and are called rare elements. Copper, silver, gold, iron, and sulphur are simple elements—_the metal irridium, for example, is a rare element_—it is the metal which tips the ends of gold pens—it is heavier than gold and much more valuable. Probably there are not two tons of it in existence.

=_A Re-agent_= is a chemical used to investigate the qualities of some other chemical—example, hydrochloric acid is a re-agent in finding carbonic acid in limestone, or carbonate of lime, which when treated by it will give up its free carbonic acid gas, which is the same as the gas in soda water.

=_An Oxide_= is any element, such as iron, aluminium, lime, magnesia, etc., combined with oxygen. To be an oxide _it must pass through the state of oxidization_. Iron after it is rusted is the oxide of iron, etc.

=_A Carbonate_= is an element, such as iron, sodium, etc., which forms a union with carbonic acid—the latter is a mixture of carbon and oxygen in the proportion of 1 part of carbon to 2 of oxygen. Carbonic acid, as is well known, does not support combustion and is one of the gases which come from perfect combustion. This acid, or what may be better termed a gas, is plentifully distributed by nature and is found principally combined with lime and magnesia, and in this state (_i.e._, carbonate of lime and carbonate of magnesia) is one of the worst enemies to a boiler.

=_An Acid_= is a liquid which contains both hydrogen and oxygen combined with some simple element such as chlorine, sulphur, etc. It will always turn blue litmus red, and has that peculiar taste known as acidity; acids range in their power from the corrosive oil of vitriol to the pleasant picric acid which gives its flavor to fruits.

=_Alkalies_= are the opposite to an acid; they are principally potash, soda and ammonia—these combined with carbonic acid form carbonates. Sal-soda is carbonate of soda.

=_A Chloride_= is an element combined with hydro chloric acid—common salt is a good example of a chloride—being sodium united with the element chlorine, which is the basis of hydro chloric acid. Chlorides are not abundant in nature but all waters contain traces of them more or less and they are not particularly dangerous to a boiler.

=_Sulphates_= are formed by the action of sulphuric acid (commercially known as the oil of vitriol) upon an element, such as sodium, magnesia, etc. The union of sodium and sulphuric acid is the well-known Glauber salts—this is nothing more than sulphate of soda; _sulphate of lime is nothing more than gypsum_. Sulphates are dangerous to boilers, if in large quantities _should they give up their free acid_—the action of the latter being to corrode the metal.

=_Silica_= is the gritty part of sand—it is also the basis of all fibrous vegetable matter—a familiar example of this is _the ash_ which shows in packing, which has been burnt by the heat in steam; by a peculiar chemical treatment silica has been made into soluble glass—a liquid. 65 per cent. of the earth’s crust is composed of silica—it is the principal part of rock—pure white sand is silica itself—it is composed of an element called _silicum_ combined with the oxygen of the air. Owing to its abundance in nature and its peculiar solubility it is found largely in all waters that come from the earth and is present in all boiler scale.

In water analysis the term _insoluble matter_, is silica. This is one of the least dangerous of all the impurities that are in feed water.

=_Magnesia_= is a fine, light, white powder, having neither taste nor smell, almost insoluble in boiling, but less so in cold water. Magnesia as found in feed water exists in two states, oxide and a carbonate, when in the latter form and free from the traces of iron, tends to give the yellow coloring matter to scale—in R. R. work, yellow scale is called magnesia scale.

=_Carbonate of Magnesia_= is somewhat more soluble in cold than in hot water, but still requires to dissolve it 9,000 parts of the latter and 2,493 of former.

Magnesia, in combination with silica, enters largely into the composition of many rocks and minerals, such as soapstone, asbestos, etc.

=_Lime_=, whose chemical name is _calcium_, is a white alkaline earthy powder obtained from the native carbonates of lime, such as the different calcerous stones and sea shells, by driving off the carbonic acid in the process of calcination or burning.

Lime is procured on a large scale by burning the stone in furnaces called kilns, either mixed with the fuel or exposed to the heated air and flames that proceed from side fires through the central cavity of the furnace in which the stones are collected.

The calcined stones may retain their original form or crumble in part to powder; if protected from air and moisture they can afterwards be preserved without change.

=_Soda_= is a grayish white solid, fusing at a red heat, volatile with difficulty, and having an intense affinity for water, with which it combines with great evolution of heat.

The only reagent which is available for distinguishing its salts from those of the other alkalies is a solution of antimoniate of potash, which gives a white precipitate even in diluted solutions.

=_Sodium_= _is the metallic base of soda._ It is silver white with a high lustre; crystallizes in cubes; of the consistence of wax at ordinary temperatures, and completely liquid at 194°, and volatilizes at a bright red heat. It is very generally diffused throughout nature though apparently somewhat less abundantly than potassium in the solid crust of the globe.

=_Salt_=, the chloride of sodium, a natural compound of one atom of chloride and one of sodium. It occurs as a rock inter-stratified with marl, and sandstones, and gypsum, and as an element of salt springs, sea water, and salt water lakes.

The proportions of its elements are 60.4 per cent. of chlorine and 39.6 per cent. of sodium.

In salt made of sea water the salts of magnesia with a little sulphate of lime are the principal impurities.

The above mentioned chemical substances can be classified into two distinct classes, _i.e._, incrusting and non-incrusting.

Of the incrusting salts, carbonate of magnesia is the most objectionable, and any feed water that contains a dozen grains per gallon of magnesia can be expected to have a most injurious effect on the boiler, causing corrosion and pitting. Carbonate of lime, while not as bad as the magnesia carbonate, yet has a very destructive action on a boiler and 20 grains per gallon of this is considered bad water. All silicates, oxides of iron, and aluminium, and sulphate of lime are also incrusting. The non-incrusting substances are three, viz., chloride of sodium (common salt), and sulphate and carbonate of soda.

NOTE.

In view of the increasing importance laid upon a knowledge of the chemical formation of feed water, these chapters of Chemical Terms and Analysis of Feed Waters are given to indicate _the direction in which the advanced engineer must push his inquiries_. There are more millions of treasure to be made by properly “treating” the water which enters the steam generators of the world than can be extracted from its gold mines.

An important “point” is to make sure, before adopting any permanent system for purifying the waters of a steam plant, that it is always the same in its ingredients, _i.e._, that the impurities contained in the water are the same at all times.

ANALYSIS OF FEED WATER.

In response to a generous offer made by a leading engineering journal, the following compositions of feed water were ascertained and published. The “Directions” show how the water was forwarded, and the tables, the result of careful examination, of samples sent from widely separated sections of the country.

DIRECTIONS.

1. Get a clean gallon jug or bottle and a new cork (or, at all events, a thoroughly clean one).

2. Wash out the vessel two or three times with the same water that is going to be sent in it. This is to make sure that the sample may not be contaminated with any “foreign” ingredient.

3. Tie the cork, after the bottle is filled with the water, with a strong string or wire. Pack the bottle so secure, with hay or straw, sawdust, or newspapers, that it may not knock itself to pieces against the sides of the box.

FROM ARGOS, IND.
Grains per
Gallon.

Silica 1.1096
Oxides of iron and aluminium .1752
Carbonate of lime 11.9010
Carbonate of magnesia 5.4597
Carbonate of soda 1.1324
Chloride of sodium .0715
-------
Total solids 19.8494

FROM SIOUX FALLS, S. D.
Grains per
Gallon.
Silica .8292
Oxides of iron and aluminium .2452
Carbonate of lime 9.0699
Carbonate of magnesia 5.4376
Chloride of sodium 1.7172
Sulphate of sodium 4.5245
Sulphate of lime 2.6976
-------
Total solids 25.0936

FROM LITCHFIELD, ILL. Grains per
Gallon.
Silica .4711
Oxides of iron and aluminium .7475
Carbonate of lime .3800
Carbonate of magnesia 2.2911
Chloride of sodium 8.7543
Sulphate of soda 16.0329
Sulphate of lime 2.8168
-------
Total solids 31.4835

FROM CHELSEA, MASS. Grains per
Gallon.
Silica .1168
Oxides of iron and aluminium .6540
Carbonate of lime 34.5260
Carbonate of magnesia 22.8470
Chloride of sodium 63.2041
Sulphate of soda 28.4711
Carbonate of soda 32.2321
--------
Total solids 182.0511

FROM MEMPHIS, TENN. Grains per
Gallon.
Silica .8292
Oxides of iron and aluminium .4789
Carbonate of lime 1.8337
Carbonate of magnesia .9956
Carbonate of soda 1.9792
------
Total solids 6.1166

FROM PEKIN, ILL. Grains per
Gallon.
Silica 1.0628
Oxides of iron and aluminium Trace
Carbonate of lime 10.0915
Carbonate of magnesia 5.8224
Chloride of soda Trace
Sulphate of soda 1.2456
-------
Total solids 18.6471

FROM TIFFIN, OHIO. Grains per
Gallon.
Silica .5256
Oxides of iron and aluminium .2336
Carbonate of lime 12.6144
Carbonate of magnesia 10.2652
Carbonate of soda 2.4137
Sulphate of soda 6.8296
Chloride of sodium 1.0484
-------
Total solids 33.9395

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.

Question.—What is corrosion?
Answer.—_Corrosion is simply rusting_ or the wasting away of the
surfaces of metals, for particulars of which see page 126.

Question.—What is incrustation?
Answer.—_Incrustation means_ simply _a coating over_.
Water, on becoming steam, is separated from the impurities which it
may have contained, and these form sediment and incrustation.

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:

Constituent. River. Brackish. Sea.
Calcic carbonate 75.85 43.65 0.97
„ sulphate 3.68 34.78 85.53
Magnesic hydrate 2.56 4.34 3.39
Sodic chloride 0.45 0.56 2.79
Silica 7.66 7.52 1.10
Oxides of iron and alumina 2.96 3.44 0.32
Organic matter 3.64 1.55 trace
Moisture 3.20 4.16 5.90
------ ------ ------
100.00 100.00 100.00

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.

Parts per 100 parts
of deposit.

Silica .042 parts.
Oxides of iron and aluminium .044 „
Carbonate of lime 30.780 „
Carbonate of magnesia 51.733 „
Sulphate of soda Trace „
Chloride of sodium Trace „
Carbonate of soda 9.341 „
Organic matter 8.060 „
--------------
Total solids 100. Parts

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 2-1/2 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:

Pounds
Sal soda 40
Catechu 5
Sal ammoniac 5

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.