It thus appears that peat which is light, loose in structure, and much mixed with clay or sand, is a poor or very poor article for producing heat: while a dense pure peat is very good.

A great drawback to the usefulness of most kinds of peat-fuel, lies in their great friability. This property renders them unable to endure transportation. The blocks of peat which are commonly used in most parts of Germany as fuel, break and crumble in handling, so that they cannot be carried far without great waste. Besides, when put into a stove, there can only go on a slow smouldering combustion as would happen in cut tobacco or saw-dust. A free-burning fuel must exist in compact lumps or blocks, which so retain their form and solidity, as to admit of a rapid draught of air through the burning ma.s.s.

The bulkiness of ordinary peat fuel, as compared with hard wood, and especially with coal, likewise renders transportation costly, especially by water, where freights are charged by bulk and not by weight, and renders storage an item of great expense.

The chief value of that peat fuel, which is simply cut from the bog, and dried without artificial condensation, must be for the domestic use of the farmer or villager who owns a supply of it not far from his dwelling, and can employ his own time in getting it out. Though worth perhaps much less cord for cord when dry than hard wood, it may be cheaper for home consumption than fuel brought from a distance.

Various processes have been devised for preparing peat, with a view to bringing it into a condition of density and toughness, sufficient to obviate its usual faults, and make it compare with wood or even with coal in heating power.

The efforts in this direction have met with abundant success as regards producing a good fuel. In many cases, however, the cost of preparation has been too great to warrant the general adoption of these processes.

We shall recur to this subject on a subsequent page, and give an account of the methods that have been proposed or employed for the manufacture of condensed peat fuel.

2.--_Density of Peat._

The apparent[10] specific gravity of peat in the air-dry state, ranges from 0.11 to 1.03. In other words, a full cubic foot weighs from one-tenth as much as, to slightly more than a cubic foot of water, = 62-1/3 lbs. Peat, which has a specific gravity of but 0.25, may be and is employed as fuel. A full cubic foot of it will weigh about 16 lbs. In Germany, the cubic foot of "good ordinary peat" in blocks,[11] ranges from 15 to 25 lbs. in weight, and is employed for domestic purposes. The heavier peat, weighing 30 or more lbs. per cubic foot in blocks, is used for manufacturing and metallurgical purposes, and for firing locomotives.

Karmarsch has carefully investigated more than 100 peats belonging to the kingdom of Hanover, with reference to their heating effect. He cla.s.sifies them as follows:--

A. _Turfy peat_, (_Rasentorf_,) consisting of slightly decomposed mosses and other peat-producing plants, having a yellow or yellowish-brown color, very soft, spongy and elastic, sp. gr. 0.11 to 0.26, the full English cubic foot weighing from 7 to 16 lbs.

B. _Fibrous peat_, unripe peat, which is brown or black in color, less elastic than turfy peat, the fibres either of moss, gra.s.s, roots, leaves, or wood, distinguishable by the eye, but brittle, and easily broken; sp. gr. 0.24 to 0.67, the weight of a full cubic foot being from 15 to 42 lbs.

C. _Earthy peat._--Nearly or altogether dest.i.tute of fibrous structure, drying to earth-like ma.s.ses which break with more or less difficulty, giving l.u.s.treless surfaces of fracture; sp. gr. 0.41 to 0.90, the full cubic foot weighing, accordingly, from 25 to 56 lbs.

D. _Pitchy peat_, (_Pechtorf_,) dense; when dry, hard; often resisting the blows of a hammer, breaking with a smooth, sometimes l.u.s.trous fracture, into sharp-angled pieces. Sp. gr. 0.62 to 1.03, the full cubic foot weighing from 38 to 55 lbs.

In Kane and Sullivan's examination of 27 kinds of Irish peat, the specific gravities ranged from 0.274 to 1.058.

3.--_Heating power of peat as compared with wood and anthracite._

Karmarsch found that in absolute heating effect

100 lbs. of turfy, air-dry peat, on the average = 95 lbs. of pine wood.

" fibrous " " " = 108 " "

" earthy " " " = 104 " "

" pitchy " " " = 111 " "

The comparison of heating power by bulk, instead of weight, is as follows:--

100 cubic ft. of turfy peat, on the average[12] = 33 cubic ft. of pine wood, in sticks.

" " fibrous " " = 90 cubic ft. of pine wood, in sticks.

" " earthy " " = 145 cubic ft. of pine wood, in sticks.

" " pitchy " " = 184 cubic ft. of pine wood, in sticks.

According to Brix, the weight per English cord and relative heating effect of several air-dry peats--the heating power of an equal bulk of oak wood being taken at 100 as a standard--are as follows, _bulk for bulk_:[13]

_Weight per _Heating cord._ effect._ Oak wood 4150 lbs. 100 Peat from Linum, 1st quality, dense and pitchy 3400 " 70 " " 2d " fibrous 2900 " 55 " " 3d " turfy 2270 " 53 Peat from Buechsenfeld, 1st quality, pitchy, very hard and heavy 3400 lbs. 74 Peat from Buechsenfeld, 2d quality 2730 " 64

These statements agree in showing, that, while weight for weight, the ordinary qualities of peat do not differ much from wood in heating power; the heating effect of _equal bulks_ of this fuel, as found in commerce, may vary extremely, ranging from one-half to three quarters that of oak wood.

Condensed peat may be prepared by machinery, which will weigh more than hard wood, bulk for bulk, and whose heating power will therefore exceed that of wood.

Gysser gives the following comparisons of a good peat with various German woods and charcoals, equal weights being employed, and split beech wood, air-dry, a.s.sumed as the standard.[14]

Beech wood, split, air dry 1.00 Peat, condensed by Weber's & Gysser's method,[15] air-dried, with 25 _per cent._ moisture. 1.00 Peat, condensed by Weber's & Gysser's method, hot-dried, with 10 _per cent._ moisture. 1.48 Peat-charcoal, from condensed peat. 1.73 The same peat, simply cut and air-dried. 0.80 Beech-charcoal. 1.90 Summer-oak wood. 1.18 Birch wood. 0.95 White pine wood. 0.72 Alder. 0.65 Linden. 0.65 Red pine. 0.61 Poplar. 0.50

Some experiments have been made in this country on the value of peat as fuel. One was tried on the N. Y. Central Railroad, Jan. 3, 1866. A locomotive with 25 empty freight cars attached, was propelled from Syracuse westward--the day being cold and the wind ahead--at the rate of 16 miles the hour. The engineer reported that "the peat gave us as much steam as wood, and burnt a beautiful fire." The peat, we infer, was cut and prepared near Syracuse, N. Y.

In one of the pumping houses of the Na.s.sau Water Department of the City of Brooklyn, an experiment has been made for the purpose of comparing peat with anthracite, for the results of which I am indebted to the courtesy of Moses Lane, Esq., Chief Engineer of the Department.

Fire was started under a steam boiler with wood. When steam was up, the peat was burned--its quant.i.ty being 1743 lbs., or 18 barrels--and after it was consumed, the firing was continued with coal. The pressure of steam was kept as nearly uniform as possible throughout the trial, and it was found that with 1743 lbs. of peat the engine made 2735 revolutions, while with 1100 lbs. of coal it made 3866 revolutions. In other words, 100 lbs. of coal produced 351-45/100 revolutions, and 100 lbs. of peat produced 156-91/100 revolutions. One pound of coal therefore equalled 2-24/100 lbs. of peat in heating effect. The peat burned well and generated steam freely.

Mr. Lane could not designate the quality of the peat, not having been able to witness the experiment.

These trials have not, indeed, all the precision needful to fix with accuracy the comparative heating effect of the fuels employed; for a furnace, that is adapted for wood, is not necessarily suited to peat, and a coal grate must have a construction unlike that which is proper for a peat fire; nevertheless they exhibit the relative merits of wood, peat, and anthracite, with sufficient closeness for most practical purposes.

Two considerations would prevent the use of ordinary cut peat in large works, even could two and one-fourth tons of it be afforded at the same price as one ton of coal. The Na.s.sau Water Department consumes 20,000 tons of coal yearly, the handling of which is a large expense, six firemen being employed to feed the furnaces. To generate the same amount of steam with peat of the quality experimented with, would require the force of firemen to be considerably increased. Again, it would be necessary to lay in, under cover, a large stock of fuel during the summer, for use in winter, when peat cannot be raised. Since a barrel of this peat weighed less than 100 lbs., the short ton would occupy the volume of 20 barrels; as is well known, a ton of anthracite can be put into 8 barrels. A given weight of peat therefore requires 2-1/2 times as much storage room, as the same weight of coal. As 2-1/4 tons of peat, in the case we are considering, are equivalent to but one ton of coal in heating effect, the winter's supply of peat fuel would occupy 5-5/8 times the bulk of the same supply in coal, admitting that the unoccupied or air-s.p.a.ce in a pile of peat is the same as in a heap of coal. In fact, the calculation would really turn out still more to the disadvantage of peat, because the air-s.p.a.ce in a bin of peat is greater than in one of coal, and coal can be excavated for at least two months more of the year than peat.

It is a.s.serted by some, that, because peat can be condensed so as to approach anthracite in specific gravity, it must, in the same ratio, approach the latter in heating power. Its effective heating power is, indeed, considerably augmented by condensation, but no mechanical treatment can increase its percentage of carbon or otherwise alter its chemical composition; hence it must forever remain inferior to anthracite.

The composition and density of the best condensed peat is compared with that of hard wood and anthracite in the following statement:--

_In 100 _Carbon._ _Hydrogen._ _Oxygen and _Ash._ _Water._ _Specific parts._ Nitrogen._ Gravity._ Wood, 39.6 4.8 34.8 0.8 20.0 0.75 Condensed peat 47.2 4.9 22.9 5.0 20.0 1.20 Anthracite 91.3 2.9 2.8 3.0 1.40

In combustion in ordinary fires, the _water_ of the fuel is a source of waste, since it consumes heat in acquiring the state of vapor. This is well seen in the comparison of the same kind of peat in different states of dryness. Thus, in the table of Gysser, (page 97) Weber's condensed peat, containing 10 _per cent._ of moisture, surpa.s.ses in heating effect that containing 25 _per cent._ of moisture, by nearly one-half.

The _oxygen_ is a source of waste, for heat as developed from fuel, is chiefly a result of the chemical union of atmospheric or free oxygen, with the carbon and hydrogen of the combustible. The oxygen of the fuel, being already combined with carbon and hydrogen, not only cannot itself contribute to the generation of heat, but neutralizes the heating effect of those portions of the carbon and hydrogen of the fuel with which it remains in combination. The quant.i.ty of heating effect thus destroyed, cannot, however, be calculated with certainty, because physical changes, viz: the conversion of solids into gases, not to speak of secondary chemical transformations, whose influence cannot be estimated, enter into the computation.

_Nitrogen_ and ash are practically indifferent in the burning process, and simply impair the heating value of fuel in as far as they occupy s.p.a.ce in it and make a portion of its weight, to the exclusion of combustible matter.

Again, as regards density, peat is, in general, considerably inferior to anthracite. The best uncondensed peat has a specific gravity of 0.90.

Condensed peat usually does not exceed 1.1. Sometimes it is made of sp.

gr. 1.3. a.s.sertions to the effect of its acquiring a density of 1.8, can hardly be credited of pure peat, though a considerable admixture of sand or clay might give such a result.

The comparative heating power of fuels is ascertained by burning them in an apparatus, so constructed, that the heat generated shall expend itself in evaporating or raising the temperature of a known quant.i.ty of water.

_The amount of heat that will raise the temperature of one gramme of water, one degree of the centigrade thermometer, is agreed upon as the unit of heat._[16]

In the complete combustion of carbon in the form of charcoal or gas-coal, there are developed 8060 units of heat. In the combustion of one gramme of hydrogen gas, 34,210 units of heat are generated. The heating effect of hydrogen is therefore 4.2 times greater than that of carbon. It was long supposed that the heating effect of compound combustibles could be calculated from their elementary composition. This view is proved to be erroneous, and direct experiment is the only satisfactory means of getting at the truth in this respect.

The data of Karmarsch, Brix, and Gysser, already given, were obtained by the experimental method. They were, however, made mostly on a small scale, and, in some cases, without due regard to the peculiar requirements of the different kinds of fuel, as regards fire s.p.a.ce, draught, etc. They can only be regarded as approximations to the truth, and have simply a comparative value, which is, however, sufficient for ordinary purposes.

The general results of the investigations. .h.i.therto made on all the common kinds of fuel, are given in the subjoined statement. The comparison is made in units of heat, and refers to equal weights of the materials experimented with.

HEATING POWER OF DIFFERENT KINDS OF FUEL.

Air-dry Wood 2800 " Peat 2500 3000 Perfectly dry Wood 3600 " " Peat 3000 4000 Air-dry Lignite or Brown Coal 3300 4200 Perfectly dry Lignite or Brown Coal 4000 5000 Bituminous Coal 3800 7000 Anthracite 7500 Wood Charcoal 6300 7500 c.o.ke 6500 7600

4.--_Modes of Burning Peat._