Chapter V: Front Matter (5)

Wood being essentially a flaming fuel is admirably adapted for use with heat-receiving surfaces of large extent, such as locomotive and marine boilers, and is also very clean in use. The absence of all cohesion in the cinders or unburnt carbonized residue causes a large amount of ignited particles to be projected from the chimney, when a rapid draught is used, unless special spark-catchers of wire gauze or some analogous contrivance are used. When burnt in open fireplaces the volatile products given off in the apartment on the first heating have an acrid penetrating odour, which is, however, very generally considered to be agreeable. Owing to the large amount of water present, no very high temperatures can be obtained by the direct combustion of wood, and to produce these for metallurgical purposes it is necessary to convert it previously either into charcoal or into inflammable gas.

Peat.

Peat includes a great number of substances of very unequal fuel value, the most recently formed spongy light brown kind approximating in composition to wood, while the dense pitchy brown compact substance, obtained from the bottom of bogs of ancient formation, may be compared with lignite or even in some instances with coal. Unlike wood, however, it contains incombustible matter in variable but large quantity, from 5 to 15% or even more. Much of this, when the amount is large, is often due to sand mechanically intermixed; when air-dried the proportion of water is from 8 to 20%. When these constituents are deducted the average composition may be stated to be--carbon, 52 to 66; hydrogen, 4.7 to 7.4; oxygen, 28 to 39; and nitrogen, 1.5 to 3%. Average air-dried peat may be taken as having a calorific value of 3000 to 3500 units, and when dried at 100 deg. C., and with a minimum of ash (4 to 5%), at about 5200 units, or from a quarter to one-third more than that of an equal weight of wood. The lighter and more spongy varieties of peat when air-dried are exceedingly inflammable, firing at a temperature of 200 deg. C.; the denser pulpy kinds ignite less readily when in the natural state, and often require a still higher temperature when prepared by pulping and compression or partial carbonization. Most kinds burn with a red smoky flame, developing a very strong odour, which, however, has its admirers in the same way that wood smoke has. This arises from the destructive distillation of imperfectly carbonized organic matter. The ash, like that of wood, is light and powdery, except when much sand is present, when it is of a denser character.

Peat is principally found in high latitudes, on exposed high tablelands and treeless areas in more temperate climates, and in the valleys of slow-flowing rivers,--as in Ireland, the west of Scotland, the tableland of Bavaria, the North German plain, and parts of the valleys of the Somme, Oise and a few other rivers in northern France. A principal objection to its use is its extreme bulk, which for equal evaporative effect is from 8 to 18 times that of coal. Various methods have been proposed, and adopted more or less successfully, for the purpose of increasing the density of raw peat by compression, either with or without pulping; the latter process gives the heaviest products, but the improvement is scarcely sufficient to compensate for the cost.

Lignite.

Lignite or brown coal is of intermediate character between peat and coal proper. The best kinds are undistinguishable in quality from free-burning coals, and the lowest earthy kinds are not equal to average peat. When freshly raised, the proportion of water may be from 45 to 50% and even more, which is reduced from 28 to 20% by exposure to dry air. Most varieties, however, when fully dried, break up into powder, which considerably diminishes their utility as fuel, as they cannot be consolidated by coking. Lignite dust may, however, be compacted into serviceable blocks for burning, by pressure in machines similar to those used for brickmaking, either in the wet state as raised from the mines or when kiln-dried at 200 deg. C. This method was adopted to a very large extent in Prussian Saxony. The calorific value varies between 3500 and 5000 units, and the evaporative factor from 2.16 when freshly raised to 5.84 for the best kinds of lignite when perfectly dried.

Other natural fuels.

Of the other natural fuels, apart from coal (q.v.), the most important is so-called vegetable refuse, such as cotton stalks, brushwood, straw, and the woody residue of sugar-cane after the extraction of the saccharine juice known as megasse or cane trash. These are extensively used in countries where wood and coal are scarce, usually for providing steam in the manufactures where they arise, e.g. straw for thrashing, cotton stalks for ploughing, irrigating, or working presses, and cane trash for boiling down sugar or driving the cane mill. According to J. Head (_Proc. Inst. of Civil Engineers_, vol. xlviii. p. 75), the evaporative values of 1 lb. of these different articles when burnt in a tubular boiler are--coal, 8 lb.; dry peat, 4 lb.; dry wood, 3.58-3.52 lb.; cotton stalks or megasse, 3.2-2.7 lb.; straw, 2.46-2.30 lb. Owing to the siliceous nature of the ash of straw, it is desirable to have a means of clearing the grate bars from slags and clinkers at short intervals, and to use a steam jet to clear the tubes from similar deposits.

The common fuel of India and Egypt is derived from the dung of camels and oxen, moulded into thin cakes, and dried in the sun. It has a very low heating power, and in burning gives off acrid ammoniacal smoke and vapour.

Somewhat similar are the tan cakes made from spent tanners' bark, which are used to some extent in eastern France and in Germany. They are made by moulding the spent bark into cakes, which are then slowly dried by exposure to the air. Their effect is about equivalent to 80 and 30% of equal weights of wood and coal respectively.

Sulphur, phosphorus and silicon, the other principal combustible elements, are only of limited application as fuels. The first is used in the liquidation of sulphur-bearing rocks. The ore is piled into large heaps, which are ignited at the bottom, a certain proportion, from one-fourth to one-third, of the sulphur content being sacrificed, in order to raise the mass to a sufficient temperature to allow the remainder to melt and run down to the collecting basin. Another application is in the so-called "pyritic smelting," where ores of copper (q.v.) containing iron pyrites, FeS2, are smelted with appropriate fluxes in a hot blast, without preliminary roasting, the sulphur and iron of the pyrites giving sufficient heat by oxidation to liquefy both slag and metal. Phosphorus, which is of value from its low igniting point, receives its only application in the manufacture of lucifer matches. The high temperature produced by burning phosphorus is in part due to the product of combustion (phosphoric acid) being solid, and therefore there is less heat absorbed than would be the case with a gaseous product. The same effect is observed in a still more striking manner with silicon, which in the only special case of its application to the production of heat, namely, in the Bessemer process of steel-making, gives rise to an enormous increase of temperature in the metal, sufficient indeed to keep the iron melted. The absolute calorific value of silicon is lower than that of carbon, but the product of combustion (silica) being non-volatile at all furnace temperatures, the whole of the heat developed is available for heating the molten iron, instead of a considerable part being consumed in the work of volatilization, as is the case with carbonic oxide, which burns to waste in the air.

Calorific power.

_Assay and Valuation of Carbonaceous Fuels._--The utility or value of
a fuel depends upon two principal factors, namely, its calorific power
and its calorific intensity or pyrometric effect, that is, the
sensible temperature of the products of combustion. The first of these
is constant for any particular product of combustion independently of
the method by which the burning is effected, whether by oxygen, air or
a reducible metallic oxide. It is most conveniently determined in the
laboratory by measuring the heat evolved during the combustion of a
given weight of the fuel. The method of Lewis Thompson is one of the
most useful. The calorimeter consists of a copper cylinder in which a
weighed quantity of coal intimately mixed with 10-12 parts of a
mixture of 3 parts of potassium chlorate and 1 of potassium nitrate is
deflagrated under a copper case like a diving-bell, placed at the
bottom of a deep glass jar filled with a known weight of water. The
mixture is fired by a fuse of lamp-cotton previously soaked in a nitre
solution and dried. The gases produced by the combustion rising
through the water are cooled, with a corresponding increase of
temperature in the latter, so that the difference between the
temperature observed before and after the experiment measures the heat
evolved. The instrument is so constructed that 30 grains (2 grammes)
of coal are burnt in 29,010 grains of water, or in the proportion of 1
to 937, these numbers being selected that the observed rise of
temperature in Fahrenheit degrees corresponds to the required
evaporative value in pounds, subject only to a correction for the
amount of heat absorbed by the mass of the instrument, for which a
special coefficient is required and must be experimentally determined.
The ordinary bomb calorimeter is also used. An approximate method is
based upon the reduction of lead oxide by the carbon and hydrogen of
the coal, the amount of lead reduced affording a measure of the oxygen
expended, whence the heating power may be calculated, 1 part of pure
carbon being capable of producing 34-1/2 times its weight of lead. The
operation is performed by mixing the weighed sample with a large
excess of litharge in a crucible, and exposing it to a bright red heat
for a short time. After cooling, the crucible is broken and the
reduced button of lead is cleaned and weighed. The results obtained by
this method are less accurate with coals containing much disposable
hydrogen and iron pyrites than with those approximating to anthracite,
as the heat equivalent of the hydrogen in excess of that required to
form water with the oxygen of the coal is calculated as carbon, while
it is really about four times as great. Sulphur in iron pyrites also
acts as a reducing agent upon litharge, and increases the apparent
effect in a similar manner.

The evaporative power of a coal found by the above methods, and also
by calculating the separate calorific factors of the components as
determined by the chemical analysis, is always considerably above that
obtained by actual combustion under a steam boiler, as in the latter
case numerous sources of loss, such as imperfect combustion of gases,
loss of unburnt coal in cinders, &c., come into play, which cannot be
allowed for in laboratory experiments. It is usual, therefore, to
determine the value of a coal by the combustion of a weighed quantity
in the furnace of a boiler, and measuring the amount of water
evaporated by the heat developed.

In a research upon the heating power and other properties of coal for
naval use, carried out by the German admiralty, the results tabulated
below were obtained with coals from different localities.

+-----------------------+-----------+------------+-----------+------------------+
| | Slag left | Ashes in | Soot in | Water evaporated |
| | in Grate. | Ashpit. | Flues. | by 1 lb. of Coal.|
+-----------------------+-----------+------------+-----------+------------------+
| Westphalian gas coals | 0.33-6.42 | 2.83- 6.53 | 0.32-0.46 | 6.60-7.45 lb. |
| Do. bituminous coals | 0.98-9.10 | 1.97- 9.63 | 0.24-0.88 | 7.30-8.66 |
| Do. dry coals | 1.93-5.70 | 4.37-10.63 | 0.24-0.48 | 7.03-8.51 |
| Silesian coals | 0.92-1.30 | 3.15- 3.50 | 0.24-0.30 | 6.73-7.10 |
| Welsh steam coals | 1.20-4.07 | 4.07 | 0.32 | 8.41 |
| Newcastle coals | 1.92 | 2.57 | 0.35 | 7.28 |
+-----------------------+-----------+------------+-----------+------------------+

The heats of combustion of elements and compounds will be found in
most of the larger works on physical and chemical constants; a
convenient series is given in the _Annuaire du Bureau des Longitudes_,
appearing in alternate years. The following figures for the principal
fuel elements are taken from the issue for 1908; they are expressed in
gramme "calories" or heat units, signifying the weight of water in
grammes that can be raised 1 deg. C. in temperature by the combustion
of 1 gramme of the substance, when it is oxidized to the condition
shown in the second column:

+----------------+---------------------------------+-----------+
| Element. | Product of Combustion. | Calories. |
+----------------+---------------------------------+-----------+
| Hydrogen \ | Water, H2O, condensed to liquid | 34,500 |
| / | " as vapour | 29,650 |
| Carbon-- | | |
| Diamond | Carbon Dioxide, CO2 | 7,868 |
| Graphite | " " | 7,900 |
| Amorphous | " " | 8,133 |
| Silicon-- | | |
| Amorphous | Silicon Dioxide, SiO2 | 6,414 |
| Crystallized | " " | 6,570 |
| Phosphorus | Phosphoric pentoxide, P2O5 | 5,958 |
| Sulphur | Sulphur dioxide, SO2, gaseous | 2,165 |
+----------------+---------------------------------+-----------+

The results may also be expressed in terms of the atomic equivalent of
the combustible by multiplying the above values by the atomic weight
of the substance, 12 for carbon, 28 for silicon, &c.

In all fuels containing hydrogen the calorific value as found by the
calorimeter is higher than that obtainable under working conditions by
an amount equal to the latent heat of volatilization of water which
reappears as heat when the vapour is condensed, though under ordinary
conditions of use the vapour passes away uncondensed. This gives rise
to the distinction of higher and lower calorific values for such
substances, the latter being those generally used in practice. The
differences for the more important compound gaseous fuels are as
follows:--

Calorific Value.
Higher. Lower.
Acetylene, C2H2 11,920 11,500
Ethylene, C2H4 11,880 11,120
Methane, CH4 13,240 11,910
Carbon monoxide, CO 2,440 2,440

Caloric intensity.

The calorific intensity or pyrometric effect of any particular fuel
depends upon so many variable elements that it cannot be determined
except by actual experiment. The older method was to multiply the
weight of the products of combustion by their specific heats, but this
gave untrustworthy results as a rule, on account of two
circumstances--the great increase in specific heat at high
temperatures in compound gases such as water and carbon dioxide, and
their instability when heated to 1800 deg. or 2000 deg. At such
temperatures dissociation to a notable extent takes place, especially
with the latter substance, which is also readily reduced to carbon
monoxide when brought in contact with carbon at a red heat--a change
which is attended with a large heat absorption. This effect is higher
with soft kinds of carbon, such as charcoal or soft coke, than with
dense coke, gas retort carbon or graphite. These latter substances,
therefore, are used when an intense local heat is required, as for
example, in the Deville furnace, to which air is supplied under
pressure. Such a method is, however, only of very special application,
the ordinary method being to supply air to the fire in excess of that
required to burn the fuel to prevent the reduction of the carbon
dioxide. The volume of flame, however, is increased by inert gas, and
there is a proportionate diminution of the heating effect. Under the
most favourable conditions, when the air employed has been previously
raised to a high temperature and pressure, the highest attainable
flame temperature from carbonaceous fuel seems to be about 2100
deg.-2300 deg. C.; this is realized in the bright spots or "eyes" of
the tuyeres of blast furnaces.

Very much higher temperatures may be reached when the products of
combustion are not volatile, and the operation can be effected by
using the fuel and oxidizing agent in the proportions exactly
required for perfect combustion and intimately mixed. These
conditions are met in the "Thermit" process of Goldschmidt, where
finely divided aluminium is oxidized by the oxide of some similar
metal, such as iron, manganese or chromium, the reaction being started
by a primer of magnesium and barium peroxide. The reaction is so
rapidly effected that there is an enormous rise in temperature,
estimated to be 5400 deg. F. (3000 deg. C.), which is sufficient to
melt the most refractory metals, such as chromium. The slag consists
of alumina which crystallizes in the forms of corundum and ruby, and
is utilized as an abrasive under the name of corubin.

The chemical examination includes the determination of (1) moisture,
(2) ash, (3) coke, (4) volatile matter, (5) fixed carbon in coke, (6)
sulphur, (7) chlorine, (8) phosphorus. Moisture is determined by
noting the loss in weight when a sample is heated at 100 deg. for
about one hour. The ash is determined by heating a sample in a muffle
furnace until all the combustible matter has been burnt off. The ash,
which generally contains silica, oxides of the alkaline earths, ferric
oxide (which gives the ash a red colour), sulphur, &c., is analysed by
the ordinary gravimetric methods. The determination of coke is very
important on account of the conclusions concerning the nature of the
coal which it permits to be drawn. A sample is finely powdered and
placed in a covered porcelain crucible, which is surrounded by an
outer one, the space between them being packed with small coke. The
crucibles are heated in a wind furnace for 1 to 1-1/2 hours, then
allowed to cool, the inner crucible removed, and the coke weighed. The
coke may be (1) pulverulent, (2) slightly fritted, (3) spongy and
swelled, (4) compact. Pulverulent cokes indicate a non-caking
bituminous coal, rich in oxygen if the amount be below 60%, but if the
amount be very much less it generally indicates a lignite; if the
amount be above 80% it indicates an anthracite containing little
oxygen or hydrogen. A fritted coke indicates a slightly coking coal,
while the spongy appearance points to a highly coking coal which has
been partly fused in the furnace. A compact coke is yielded by good
coking coals, and is usually large in amount. The volatile matters are
determined as the loss of weight on coking less the amount of
moisture. The "fixed carbon" is the carbon retained in the coke, which
contains in addition the ash already determined. The fixed carbon is
therefore the difference between the coke and the ash, and may be
determined from these figures; or it may be determined directly by
burning off the coke in a muffle and noting the loss in weight.
Sulphur may be present as (1) organic sulphur, (2) as iron pyrites or
other sulphides, (3) as the sulphates of calcium, aluminium and other
metals; but the amount is generally so small that only the total
sulphur is determined. This is effected by heating a mixture of the
fuel with lime and sodium carbonate in a porcelain dish to redness in
a muffle until all the carbonaceous matter has been burnt off. The
residue, which contains the sulphur as calcium sulphate, is
transferred to a beaker containing water to which a little bromine has
been added. Hydrochloric acid is carefully added, the liquid filtered
and the residue washed. To the filtrate ammonia is added, and then
barium chloride, which precipitates the sulphur as barium sulphate.
Sulphur existing in the form of sulphates may be removed by washing a
sample with boiling water and determining the sulphuric acid in the
solution. The washed sample is then fused in the usual way to
determine the proportion of sulphur existing as iron pyrites. The
distinction between sulphur present as sulphate and sulphide is of
importance in the examination of coals intended for iron smelting, as
the sulphates of the earthy metals are reduced by the gases of the
furnace to sulphides, which pass into the slag without affecting the
quality of the iron produced, while the sulphur of the metallic
sulphides in the ash acts prejudicially upon the metal. Coals for
gas-making should contain little sulphur, as the gases produced in the
combustion are noxious and have very corrosive properties. Chlorine is
rarely determined, but when present in quantity it corrodes copper and
brass boiler tubes, with which consequently chlorine-bearing coals
cannot be used. The element is determined by fusing with soda lime in
a muffle, dissolving the residue in water and precipitating with
silver nitrate. Phosphorus is determined in the ash by fusing it with
a mixture of sodium and potassium carbonates, extracting the residue
with hydrochloric acid, and twice evaporating to dryness with the same
acid. The residue is dissolved in hydrochloric acid, a few drops of
ferric chloride added, and then ammonia in excess. The precipitate of
ferric phosphate is then treated as in the ordinary estimation of
phosphates. If it be necessary to determine the absolute amount of
carbon and hydrogen in a fuel, the dried sample is treated with copper
oxide as in the ordinary estimation of these elements in organic
compounds. (H. B.)

_Liquid Fuel._

Vegetable oil is not used for fuel except for laboratory purposes, partly because its constituent parts are less adaptable for combustion under the conditions necessary for steam-raising, but chiefly because of the commercial difficulty of producing it with sufficient economy to compete with mineral fuel either solid or liquid.

The use of petroleum as fuel had long been recognized as a scientific possibility, and some attempts had been made to adopt it in practice upon a commercial scale, but the insufficiency, and still more the irregularity, of the supplies prevented it from coming into practical use to any important extent until about 1898, when discoveries of oil specially adapted by chemical composition for fuel purposes changed the aspect of the situation. These discoveries of special oil were made first in Borneo and later in Texas, and experience in treating the oils from both localities has shown that while not less adapted to produce kerosene or illuminating oil, they are better adapted to produce fuel oil than either the Russian or the Pennsylvanian products. Texas oil did not hold its place in the market for long, because the influx of water into the wells lowered their yield, but discoveries of fuel oil in Mexico have come later and will help to maintain the balance of the world's supply, although this is still a mere fraction of the assured supply of coal.

With regard to the chemical properties of petroleum, it is not necessary to say more in the present place than that the lighter and more volatile constituents, known commercially as naphtha and benzene, must be removed by distillation in order to leave a residue composed principally of hydrocarbons which, while containing the necessary carbon for combustion, shall be sufficiently free from volatile qualities to avoid premature ignition and consequent danger of explosion. Attempts have been made to use crude oil for fuel purposes, and these have had some success in the neighbourhood of the oil wells and under boilers of unusually good ventilation both as regards their chimneys and the surroundings of their stokeholds; but for reasons both of commerce and of safety it is not desirable to use crude oil where some distillation is possible. The more complete the process of distillation, and the consequent removal of the volatile constituents, the higher the flash-point, and the more turgid and viscous is the fuel resulting; and if the process is carried to an extreme, the residue or fuel becomes difficult to ignite by the ordinary process of spraying or atomizing mechanically at the moment immediately preceding combustion. The proportions which have been found to work efficiently in practice are as follows:--

Carbon 88.00 %
Hydrogen 10.75 %
Oxygen 1.25 %
---------
Total 100

The standards of safety for liquid fuel as determined by flash-point are not yet finally settled, and are changing from time to time. The British admiralty require a flash-point of 270 deg. F., and to this high standard, and the consequent viscosity of the fuel used by vessels in the British fleet, may partly be attributed the low rate of combustion that was at first found possible in them. The German admiralty have fixed a flash-point of 187 deg. F., and have used oil of this standard with perfect safety, and at the same time with much higher measure of evaporative duty than has been attained in British war-vessels. In the British mercantile marine Lloyd's Register has permitted fuel with a flash-point as low as 150 deg. F. as a minimum, and no harm has resulted. The British Board of Trade, the department of the government which controls the safety of passenger vessels, has fixed a higher standard upon the basis of a minimum of 185 deg. In the case of locomotives the flash-point as a standard of safety is of less importance than in the case of stationary or marine boilers, because the storage is more open, and the ventilation, both of the storage tanks and the boilers during combustion, much more perfect than in any other class of steam-boilers.

The process of refining by distillation is also necessary to reduce two impurities which greatly retard storage and combustion, i.e. water and sulphur. Water is found in all crude petroleum as it issues from the wells, and sulphur exists in important quantities in oil from the Texas wells. Its removal was at first found very expensive, but there no longer exists difficulty in this respect, and large quantities of petroleum fuel practically free from sulphur are now regularly exported from Texas to New York and to Europe.

Water mixed with fuel is in intimate mechanical relation, and frequently so remains in considerable quantities even after the process of distillation. It is in fact so thoroughly mixed as to form an emulsion. The effect of feeding such a mixture into a furnace is extremely injurious, because the water must be decomposed chemically into its constituents, hydrogen and oxygen, thus absorbing a large quantity of heat which would otherwise be utilized for evaporation. Water also directly delays combustion by producing from the jet a long, dull, red flame instead of a short bright, white flame, and the process of combustion, which should take place by vaporization of the oil near the furnace mouth, is postponed and transferred to the upper part of the combustion-box, the tubes, and even the base of the chimney, producing loss of heat and injury to the boiler structure. The most effective means of ridding the fuel of this dangerous impurity is by heat and settlement. The coefficients of expansion of water and oil by heat are substantially different, and a moderate rise of temperature therefore separates the particles and precipitates the water, which is easily drawn off--leaving the oil available for use. The heating and precipitation are usually performed upon a patented system of settling tanks and heating apparatus known as the Flannery-Boyd system, which has proved itself indispensable for the successful use at sea of petroleum fuel containing any large proportion of water.

Progress of liquid fuel.

The laboratory and mechanical use of petroleum for fuel has already been referred to, but it was not until the year 1870 that petroleum was applied upon a wider and commercial scale. In the course of distillation of Russian crude petroleum for the production of kerosene or lamp oil, large quantities of refuse were produced--known by the Russian name of _astatki_--and these were found an incumbrance and useless for any commercial purpose. To a Russian oil-refiner gifted with mechanical instinct and the genius for invention occurred the idea of utilizing the waste product as fuel by spraying or atomizing it with steam, so that, the thick and sluggish fluid being broken up into particles, the air necessary for combustion could have free access to it. The earliest apparatus for this purpose was a simple piece of gas-tube, into which the thick oil was fed; by another connexion steam at high pressure was admitted to an inner and smaller tube, and, the end of the tube nearest to the furnace being open, the pressure of the steam blew the oil into the furnace, and by its velocity broke it up into spray. The apparatus worked with success from the first. Experience pointed out the proper proportionate sizes for the inlets of steam and oil, the proper pressure for the steam, and the proportionate sizes for the orifices of admission to the furnaces, as well as the sizes of air-openings and best arrangements of fire-bricks in the furnaces themselves; and what had been a waste product now became a by-product of great value. Practically all the steam power in South Russia, both for factories and navigation of the inland seas and rivers, is now raised from _astatki_ fuel.

In the Far East, including Burma and parts of China and Japan, the use of liquid fuel spread rapidly during the years 1899, 1900 and 1901, owing entirely to the development of the Borneo oil-fields by the enterprise of Sir Marcus Samuel and the large British corporation known as the Shell Transport and Trading Company, of which he is the head. This corporation has since amalgamated with the Royal Dutch Petroleum Company controlling the extensive wells in Dutch Borneo, and together they supply large quantities of liquid fuel for use in the Far East. In the United States of America liquid fuel is not only used for practically the whole of the manufacturing and locomotive purposes of the state of Texas, but factories in New York, and a still larger number in California, are now discarding the use of coal and adopting petroleum, because it is more economical in its consumption and also more easily handled in transit, and saves nearly all the labour of stoking. So far the supplies for China and Japan have been exported from Borneo, but the discoveries of new oil-fields in California, of a character specially adapted for fuel, have encouraged the belief that it may be possible to supply Chile and Peru and other South American countries, where coal is extremely expensive, with Californian fuel; and it has also found its way across the Pacific to Japan. There are believed to be large deposits in West Africa, but in the meantime the only sources of supply to those parts of Africa where manufacture is progressing, i.e. South Africa and Egypt, are the oil-fields of Borneo and Texas, from which the import has well begun, from Texas to Alexandria via the Mediterranean, and from Borneo to Cape Town via Singapore.

In England, notwithstanding the fact that there exist the finest coal-fields in the world, there has been a surprising development of the use of petroleum as fuel. The Great Eastern railway adapted 120 locomotive engines to its use, and these ran with regularity and success both on express passenger and goods trains until the increase in price due to short supply compelled a return to coal fuel. The London, Brighton & South Coast railway also began the adaptation of some of their locomotive engines, but discontinued the use of liquid fuel from the same cause. Several large firms of contractors and cement manufacturers, chiefly on the banks of the Thames, made the same adaptations which proved mechanically successful, but were not continued when the price of liquid fuel increased with the increased demand.

Economy of liquid fuel.

The chief factors of economy are the greater calorific value of oil than coal (about 16 lb. of water per lb. of oil fuel evaporated from a temperature of 212 deg. F.), not only in laboratory practice, but in actual use on a large scale, and the saving of labour both in transit from the source of supply to the place of use and in the act of stoking the furnaces. The use of cranes, hand labour with shovels, wagons and locomotives, horses and carts, is unavoidable for the transit of coal; and labour to trim the coal, to stoke it when under combustion, and to handle the residual ashes, are all indispensable to steam-raising by coal. On the other hand, a system of pipes and pumps, and a limited quantity of skilled labour to manage them, is all that is necessary for the transit and combustion of petroleum fuel; and it is certain that even in England will be found places which, from topographical and other circumstances, will use petroleum more economically than coal as fuel for manufacturing purposes under reasonable conditions of price for the fuel.

The theoretical calorific value of oil fuel is more nearly realized in practice than the theoretical calorific value of coal, because the facilities for complete combustion, due to the artificial admixture of the air by the atomizing process, are greater in the case of oil than coal, and for this reason, among others, the practical evaporative results are proportionately higher with liquid fuel. In some cases the work done in a steam-engine by 2 tons of coal has been performed by 1 ton of oil fuel, but in others the proportions have been as 3 to 2, and these latter can be safely relied on in practice as a minimum. This saving, combined with the savings of labour and transit already explained, will in the near future make the use of liquid fuel compulsory, except in places so near to coal-fields that the cost of coal becomes sufficiently low to counterbalance the savings in weight of fuel consumed and in labour in handling it. In some locomotives on the Great Eastern railway the consumption of oil and coal for the same development of horse-power was as 17 lb. oil is to 35 lb. coal; all, however, did not realize so high a result.

Liquid fuel in locomotives.

The mechanical apparatus for applying petroleum to steam-raising in locomotives is very simple. The space in the tender usually occupied by coal is closed up by steel-plating closely riveted and tested, so as to form a storage tank. From this tank a feed-pipe is led to a burner of the combined steam-and-oil type already indicated, and this burner is so arranged as to enter a short distance inside the furnace mouth. The ordinary fire-bars are covered with a thin layer of coal, which starts the ignition in the first place, and the whole apparatus is ready for work. The burner best adapted for locomotive practice is the Holden Burner (fig. 1), which was used on the Great Eastern railway. The steam-pipe is connected at A, the oil-pipe at B, and the hand-wheels C and D are for the adjustment of the internal orifices according to the rate of combustion required. The nozzle E is directed towards the furnace, and the external ring FF, supplied by the small pipe G and the by-pass valve H, projects a series of steam jets into the furnace, independent of the injections of atomized fuel, and so induces an artificial inrush of air for the promotion of combustion. This type of burner has also been tried on stationary boilers and on board ship. It works well, although the great consumption of steam by the supplementary ring is a difficulty at sea, where the water lost by the consumption of steam cannot easily be made up.

Liquid fuel at sea.

Although the application of the new fuel for land and locomotive boilers has already been large, the practice at sea has been far more extensive. The reason is chiefly to be found in the fact that although the sources of supply are at a distance from Great Britain, yet they are in countries to whose neighbourhood British steamships regularly trade, and in which British naval squadrons are regularly stationed, so that the advantages of adopting liquid fuel have been more immediate and the economy more direct. The certainty of continuous supply of the fuel and the wide distribution of storage stations have so altered the conditions that the general adoption of the new fuel for marine purposes becomes a matter of urgency for the statesman, the merchant and the engineer. None of these can afford to neglect the new conditions, lest they be noted and acted upon by their competitors. Storage for supply now exists at a number of sea ports: London, Barrow, Southampton, Amsterdam, Copenhagen, New Orleans, Savannah, New York, Philadelphia, Singapore, Hong Kong, Madras, Colombo, Suez, Hamburg, Port Arthur, Rangoon, Calcutta, Bombay, Alexandria, Bangkok, Saigon, Penang, Batavia, Surabaya, Amoy, Swatow, Fuchow, Shanghai, Hankow, Sydney, Melbourne, Adelaide, Zanzibar, Mombasa, Yokohama, Kobe and Nagasaki; also in South African and South American ports.

The British admiralty have undertaken experiments with liquid fuel at sea, and at the same time investigations of the possibility of supply from sources within the regions of the British empire. There is an enormous supply of shale under the north-eastern counties of England, but no oil that can be pumped--still less oil with a pressure above it so as to "gush" like the wells in America--and the only sources of liquid supply under the British flag appear to be in Burma and Trinidad. The Borneo fields are not under British control, although developed entirely by British capital. The Italian admiralty have fitted several large warships with boiler apparatus to burn petroleum. The German admiralty are regularly using liquid fuel on the China station. The Dutch navy have fitted coal fuel and liquid fuel furnaces in combination, so that the smaller powers required may be developed by coal alone, and the larger powers by supplementing coal fuel with oil fuel. The speeds of some vessels of the destroyer type have by this means been accelerated nearly two knots.

Advantages in warships.

The questions which govern the use of fuel in warships are more largely those of strategy and fighting efficiency than economy of evaporation. Indeed, the cost of constructing and maintaining in fighting efficiency a modern warship is so great that the utmost use strategically must be obtained from the vessel, and in this comparison the cost of fuel is relatively so small an item that its increase or decrease may be considered almost a negligible quantity. The desideratum in a warship is to obtain the greatest fighting efficiency based on the thickest armour, the heaviest and most numerous guns, the highest maximum speed, and, last and not least, the greatest range of effective action based upon the maximum supplies of fuel, provisions and other consumable stores that the ship can carry. Now, if by changing the type of fuel it be possible to reduce its weight by 30%, and to abolish the stokers, who are usually more than half the ship's company, the weight saved will be represented not merely by the fuel, but by the consumable stores otherwise necessary for the stokers. Conversely, the radius of effective action of the ship will be doubled as regards consumable stores if the crew be halved, and will be increased by 50% if the same weight of fuel be carried in the form of liquid instead of coal. In space the gain by using oil fuel is still greater, and 36 cubic feet of oil as stored are equal in practical calorific value to 67 cubic feet of coal according to the allowance usual for ship's bunkering. On the other hand, coal has been relied upon, when placed in the side bunkers of unarmoured ships, as a protection against shot and shell, and this advantage, if it really exists, could not be claimed in regard to liquid fuel.

Recent experiments in coaling warships at sea have not been very successful, as the least bad weather has prevented the safe transmission of coal bags from the collier to the ship. The same difficulty does not exist for oil fuel, which has been pumped through flexible tubing from one ship to the other even in comparatively rough weather. Smokelessness, so important a feature of sea strategy, has not always been attained by liquid fuel, but where the combustion is complete, by reason of suitable furnace arrangements and careful management, there is no smoke. The great drawback, however, to the use of liquid fuel in fast small vessels is the confined space allotted to the boilers, such confinement being unavoidable in view of the high power concentrated in a small hull. The British admiralty's experiments, however, have gone far to solve the problem, and the quantity of oil which can be consumed by forced draught in confined boilers now more nearly equals the quantity of coal consumed under similar conditions. All recent vessels built for the British navy are so constructed that the spaces between their double bottoms are oil-tight and capable of storing liquid fuel in the tanks so formed. Most recent battleships and cruisers have also liquid fuel furnace fittings, and in 1910 it already appeared probable that the use of oil fuel in warships would rapidly develop.

In view of recent accusations of insufficiency of coal storage in foreign naval depots, by reason of the allegation that coal so stored quickly perishes, it is interesting to note that liquid fuel may be stored in tanks for an indefinite time without any deterioration whatever.

Advantages in merchant ships.

In the case of merchant steamers large progress has also been made. The Shell Transport and Trading Company have twenty-one vessels successfully navigating in all parts of the world and using liquid fuel. The Hamburg-American Steamship Company have four large vessels similarly fitted for oil fuel, which, however, differ in furnace arrangements, as will be hereafter described, although using coal when the fluctuation of the market renders that the more economical fuel. One of the large American transatlantic lines is adopting liquid fuel, and French, German, Danish and American mercantile vessels are also beginning to use it in considerable amounts.

In the case of very large passenger steamers, such as those of 20 knots and upwards in the Atlantic trade, the saving in cost of fuel is trifling compared with the advantage arising from the greater weight and space available for freight. Adopting a basis of 3 to 2 as between coal consumption and oil consumption, there is an increase of 1000 tons of dead weight cargo in even a medium-sized Atlantic steamer, and a collateral gain of about 100,000 cub. ft. of measurement cargo, by reason of the ordinary bunkers being left quite free, and the oil being stored in the double bottom spaces hitherto unutilized except for the purpose of water ballast. The cleanliness and saving of time from bunkering by the use of oil fuel is also an important factor in passenger ships, whilst considerable additional speed is obtainable. The cost of the installation, however, is very considerable, as it includes not only burners and pipes for the furnaces, but also the construction of oil-tight tanks, with pumps and numerous valves and pipe connexions.

Fig. 2 shows a burner of Rusden and Eeles' patent as generally used on
board ships for the purpose of injecting the oil. A is a movable cap
holding the packing B, which renders the annular spindle M oil and
steam tight. E is the outer casing containing the steam jacket from
which the steam, after being fed through the steam-supply pipe G,
passes into the annular space surrounding the spindle P. It will be
seen that if the spindle P be travelled inwards by turning the handle
N, the orifice at the nozzle RR will be opened so as to allow the
steam to flow out radially. If at the same time the annular spindle M
be drawn inwards by revolving the handle L, the oil which passes
through the supply pipe F will also have emission at RR, and, coming
in contact with the outflowing steam, will be pulverized and sprayed
into the furnace. Fig. 3 is a profile and plan of a steamer adapted
for carrying oil in bulk, and showing all the storage arrangements for
handling liquid fuel. Fig. 4 shows the interior arrangement of the
boiler furnace of the steamship "Trocas." A is broken fire-brick
resting on the ordinary fire-bars, B is a brick bridge, C a casing of
fire-brick intended to protect the riveted seam immediately above it
from the direct impact of the flame, and D is a lining of fire-brick
at the back of the combustion-box, also intended to protect the
plating from the direct impact of the petroleum flame. The arrangement
of the furnace on the Meyer system is shown in fig. 5, where E is an
annular projection built at the mouth of the furnace, and BB are
spiral passages for heating the air before it passes into the furnace.
Fig. 6 shows the rings CC and details of the casting which forms the
projection or exterior elongation of the furnace. The brickwork
arrangement adopted for the double-ended boilers on the
Hamburg-American Steamship Company's "Ferdinand Laeisz" is represented
in fig. 7. The whole furnace is lined with fire-brick, and the burner
is mounted upon a circular disk plate which covers the mouth of the
furnace. The oil is injected not by steam pulverization, but by
pressure due to a steam-pump. The oil is heated to about 60 deg. C.
before entering the pump, and further heated to 90 deg. C. after
leaving the pump. It is then filtered, and passes to the furnace
injector C at about 30-lb. pressure; and its passage through this
injector and the spiral passages of which it consists pulverizes the
oil into spray, in which form it readily ignites on reaching the
interior of the furnace. The injector is on the Korting principle,
that is, it atomizes by fracture of the liquid oil arising from its
own momentum under pressure. The advantage of this system as compared
with the steam-jet system is the saving of fresh water, the
abstraction of which is so injurious to the boiler by the formation of
scale.

The general arrangement of the fuel tanks and filling pipes on the ss.
"Murex" is shown in fig. 8; and fig. 9 represents the furnace gear of
the same vessel, A being the steam-pipe, B the oil-pipe, C the
injector, D the swivel upon which the injector is hung so that it may
be swung clear of the furnace, E the fire-door, and F the handle for
adjusting the injector. In fig. 10, which represents a section of the
furnace, H is a fire-brick pier and K a fire-brick baffling bridge.

It is found in practice that to leave out the fire-bars ordinarily
used for coal produces a better result with liquid fuel than the
alternative system of keeping them in place and protecting them by a
layer of broken fire-brick.

Boilers fitted upon all the above systems have been run for thousands
of miles without trouble. In new construction it is desirable to give
larger combustion chambers and longer and narrower boiler tubes than
in the case of boilers intended for the combustion of coal alone.
(F. F.*)

_Gaseous Fuel._

Strictly speaking, much, and sometimes even most, of the heating effected by solid or liquid fuel is actually performed by the gases given off during the combustion. We speak, however, of gaseous fuel only in those cases where we supply a combustible gas from the outset, or where we produce from ordinary solid (or liquid) fuel in one place a stream of combustible gas which is burned in another place, more or less distant from that where it has been generated.

The various descriptions of gaseous fuel employed in practice may be
classified under the following heads:

I. Natural Gas.

II. Combustible Gases obtained as by-products in various technical
operations.

III. Coal Gas (Illuminating Gas).

IV. Combustible Gases obtained by the partial combustion of coal, &c.

I. _Natural Gas._--From time immemorial it has been known that in some parts of the Caucasus and of China large quantities of gases issue from the soil, sometimes under water, which can be lighted and burn with a luminous flame. The "eternal fires" of Baku belong to this class. In coal-mines frequently similar streams of gas issue from the coal; these are called "blowers," and when they are of somewhat regular occurrence are sometimes conducted away in pipes and used for underground lighting. As a regular source of heating power, however, natural gas is employed only in some parts of the United States, especially in Pennsylvania, Kansas, Ohio and West Virginia, where it always occurs in the neighbourhood of coal and petroleum fields. The first public mention of it was made in 1775, but it was not till 1821 that it was turned to use at Fredonia, N.Y. In Pennsylvania natural gas was discovered in 1859, but at first very little use was made of it. Its industrial employment dates only from 1874, and became of great importance about ten years later. Nobody ever doubted that the gas found in these localities was an accumulation of many ages and that, being tapped by thousands of bore-holes, it must rapidly come to an end. This assumption was strengthened by the fact that the "gas-wells," which at first gave out the gas at a pressure of 700 or 800, sometimes even of 1400 lb. per sq. in., gradually showed a more and more diminishing pressure and many of them ceased to work altogether. About the year 1890 the belief was fairly general that the stock of natural gas would soon be entirely exhausted. Indeed, the value of the annual production of natural gas in the United States, computed as its equivalent of coal, was then estimated at twenty-one million dollars, in 1895 at twelve millions, in 1899 at eleven and a half millions. But the output rose again to a value of twenty-seven millions in 1901, and to fifty million dollars in 1907. Mostly the gas, derived from upwards of 10,000 gas-wells, is now artificially compressed to a pressure of 300 or 400 lb. per sq. in. by means of steam-power or gas motors, fed by the gas itself, and is conveyed over great distances in iron pipes, from 9 or 10 to 36 in. in diameter. In 1904 nearly 30,000 m. of pipe lines were in operation. In 1907 the quantity of natural gas consumed in the United States (nearly half of which was in Pennsylvania) was 400,000 million cub. ft., or nearly 3 cub. m. Canada (Ontario) also produces some natural gas, reaching a maximum of about $746,000 in 1907.

The principal constituent of natural gas is always methane, CH4, of which it contains from 68.4 to 94.0% by volume. Those gases which contain less methane contain all the more hydrogen, viz. 2.9 to 29.8%. There is also some ethylene, ethane and carbon monoxide, rarely exceeding 2 or 3%. The quantity of incombustible gases--oxygen, carbon dioxide, nitrogen--ranges from mere traces to about 5%. The density is from 0.45 to 0.55. The heating power of 1000 cub. ft. of natural gas is equal to from 80 to 120 lb., on the average 100 lb., of good coal, but it is really worth much more than this proportion would indicate, as it burns completely, without smoke or ashes, and without requiring any manual labour. It is employed for all domestic and for most industrial purposes.

The origin of natural gas is not properly understood, even now. The most natural assumption is, of course, that its formation is connected with that of the petroleum always found in the same neighbourhood, the latter principally consisting of the higher-boiling aliphatic hydrocarbons of the methane series. But whence do they both come? Some bring them into connexion with the formation of coal, others with the decomposition of animal remains, others with that of _diatomaceae_, &c., and even an inorganic origin of both petroleum and natural gas has been assumed by chemists of the rank of D.I. Mendeleeff and H. Moissan.

II. _Gases obtained as By-products._--There are two important cases in which gaseous by-products are utilized as fuel; both are intimately connected with the manufacture of iron, but in a very different way, and the gases are of very different composition.

(a) _Blast-furnace Gases._--The gases issuing from the mouths of blast-furnaces (see IRON AND STEEL) were first utilized in 1837 by Faber du Faur, at Wasseralfingen. Their use became more extensive after 1860, and practically universal after 1870. The volume of gas given off per ton of iron made is about 158,000 cub. ft. Its percentage composition by volume is:

Carbon monoxide 21.6 to 29.0, mostly about 26%
Hydrogen 1.8 " 6.3, " " 3%
Methane 0.1 " 0.8, " " 0.5%
Carbon dioxide 6 " 12, " " 9.5%
Nitrogen 51 " 60, " " 56 %
Steam 5 " 12, " " 5 %
-----
100 %

There is always a large amount of mechanically suspended flue-dust in this gas. It is practically equal to a poor producer-gas (see below), and is everywhere used, first for heating the blast in Cowper stoves or similar apparatus, and secondly for raising all the steam required for the operation of the blast-furnace, that is, for driving the blowing-engines, hoisting the materials, &c. Where the iron ore is roasted previously to being fed into the furnace, this can also be done by this gas, but in some cases the waste in using it is so great that there is not enough left for the last purpose. The calorific power of this gas per cubic foot is from 80 to 120 B.Th.U.