Kingdom.]
179
Class 1 . — MINING AND MINERAL PRODUCTS.
by its decomposition a clayey coating, they are consider-able; the thickness of the bog (for example in Knock-laid, in the county of Antrim, which is 1,685 feet high)being nearly 12 feet. The summit bogs of high moun-tains are distinguishable from those of lower levels, bythe total absence of large trees.
As turf includes a mass of plants in different stages ofdecomposition, its aspect and constitution vary verymuch. Near the surface it is light-coloured, spongy,and contains the vegetable matter but little altered;deeper it is brown, denser, and more decomposed; andfinally, at the base of the greater bogs, some of whichpresent a depth of 40 feet, the mass of turf assumes theblack colour, and nearly the density of coal, to whichalso it approximates very much in chemical composition.The amount of ash contained in turf is also variable, andappeal’s to increase in proportion as we descend. Thus,in the section of a bog 40 feet deep, at Timahoe, thoseportions near the surface contained 1J per cent, of ashes,the centre portions 3J per cent., whilst the lowest fourfeet of turf, contained 19 percent, of ashes. In thesuperficial layers, it may also be remarked, that the com-position is nearly the same as that of wood, the vegetablematerial being but little altered, and in the lower we findthe change into coal nearly complete. Notwithstandingthese extreme variations, we may yet establish the ordi-nary constitution of turf with certainty enough for prac-tical use, and, on the average specimens of turf selectedfrom various localities, the following results have beenobtained :—
The calorific power of dry turf is about half that ofcoal; it yields, when ignited with litharge, about four-teen times its weight of lead. This power is, however,immensely diminished in ordinary use, by the waterwhich is allowed to remain in its texture, and of whichthe spongy character of its mass renders it very difficultto get rid. There is nothing which requires more altera-tion than the collection and preparation of turf; indeed,for practical purposes, this valuable fuel is absolutelyspoiled as it is now prepared in Ireland . It is cut in a wetseason of the year; whilst drying it is exposed to the wea-ther; it hence is in reality not dried at all. It is veryusual to find the turf of commerce containing one-fourth ofits weight of water, although it then feels dry to the hand.But let us examine how that affects its calorific power.One pound of pure dry turf will evaporate 6 lbs. of water;now in 1 lb. of turf, as usually found, there are j lb, ofdry turf, and 1? lb. of water. The j lb. can only evapo-rate 4s lbs. of water; but out of this it must first evapo-rate the J lb. contained in its mass, and hence the waterboiled away by 1 lb. of such turf is reduced to 4J lbs.The loss is here 30 per cent., a proportion which makesall the difference between a good fuel and one almostunfit for use. When turf is dried in the air, under cover,it still retains one-tenth of its weight of water, whichreduces its calorific power 12 per cent., 1 lb. of such turfevaporating lbs. of water. This effect is sufficient,however, for the great majority of objects; the furtherdesiccation is too expensive and too troublesome to beused, except in some especial cases.
The characteristic fault of turf as a fuel is its want ofdensity, which renders it difficult to concentrate withina limited space the quantity of heat necessary for manyoperations. The manner of heating turf is, indeed, justrhe opposite to that of anthracite. The turf yields ayast body of volatile inflammable ingredients, which passinto the flues and chimney, and thus distribute the heatof combustion over a great space, whilst in no one pointis the heat intense. Hence for all flaming fires turf isapplicable, and in its application to boilers it is pecu-liarly useful, as there is no liability to that burning awayof the metal, which may arise from the local intensity ofthe heat of coke or coal. If it be required, it is quitepossible, however, to obtain a very intense heat withturf.
^h e removal of the porosity and elasticity of turf, sothat it may assume the solidity of coal, has been the ob-ject of many who have proposed mechanical and otherprocesses for the purpose. It has been found that the
elasticity of the turf fibre presents great obstacles tocompression, and the black turf, which is not fibrous, isof itself, sufficiently dense.
Not merely may we utilize turf in its natural condi-tion, or compressed, or impregnated with pitchy matter,but we may carbonize it, as we do wood, and prepareturf charcoal, the properties of which it is important toestablish. The methods of carbonization are of twokinds:—1. By heating turf in close vessels; by this modeloss is avoided, but it is expensive, and there is no com-pensation in the distilled liquors, which do not containacetic acid in any quantity. The tar is often small inquantity, and the gases are deficient in illuminatingpower, hence the charcoal is the only valuable product.Its quantity varies from 30 to 40 per cent, by weightof the dry turf. The products of the distillation of1,157 lbs. of turf were found by Blavier to be—charcoal,474 lbs., or 41 per cent. ; watery liquid, 226 lbs., or 19*3per cent.; gaseous matter, 450 lbs., or 39 per cent.; andtar, 7 lbs., or 6 per cent.; but the proportion of tar isvariable, sometimes reaching to 24*5 per cent, whencoked in close vessels.
The economical carbonization of turf is best carried onin heaps, in the same manner as that of wood. Thesods must be regularly arranged, and laid as close aspossible; they are the better for being large—15 incheslong, by 6 broad, and 5 deep. The heaps, built hemi-spherically, should be smaller in size than the heaps ofwood usually are. In general 5,000 or 6,000 large sodsmay go to a heap, which will thus contain 1,500 cubicfeet. The mass must be allowed to heat more than isnecessary for wood, and the process requires to be verycarefully attended to, from the extreme combustibilityof the charcoal. The quantity of charcoal obtained inthis mode of carbonization is from 25 to 30 per cent, ofthe weight of dry turf.
The charcoal so obtained is very light and very inflam-mable; it possesses nearly the volume of the turf. Itusually burns with a light flame, as the volatile mattersare not totally expelled. This is shown by the com-
position of a specimen analyzed with the followingresult :—
Hydrogen.1*70
Oxygen and nitrogen . . 4*20
Ashes.4-20
100-00
For many industrial uses the charcoal so prepared istoo light, as, generally speaking, it is only with fuelsof considerable density that the most intense heat canbe produced; but by coking compressed turf, it hasbeen already shown that the resulting charcoal mayattain a density of 1,040, which is far superior to that ofwood charcoal, and even equal to that of the best cokemade from coal. As to calorific effect, turf charcoal isabout the same as coal cokes, and little inferior to woodcharcoal.
It is peculiarly important, in the preparation of thecharcoal from turf, that the material should be selectedas free as possible from earthy impurities, for all suchare concentrated in the coke, which may be thereby ren-dered of little comparative value. Hence the coke fromsurface turf contains less than 10 per cent, of ash, whilstthat of the dense turf of the lower strata contains from20 to 30 per cent. This latter quantity might altogetherunfit it for practical purposes.
The above account of turf and its value, for whichwe are much indebted to the work of Sir Robert Kane ,on the Industrial Resources of Ireland, will be found toapply in an important way to many experiments latelytried with this kind of fuel, and illustrated by severalobjects exhibited by Mr. Cobbold, Mr. Reece Rees, Mr.J. Rogers, and others. The products obtained for eco-nomic use, by the more careful distillation of turf andpeat, will be fully described by reference to the body ofthe Catalogue.