1845.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



343 



nished to tlie Government at full prices did not answer the expecta- 

 tions of those concerned in their consumption. While paying the 

 highest prices for fuel, the efficiency of our steam vessels was some- 

 times impaired by its inferior quality, and the large amount of its im- 

 purity. 



While so large an amount of both labour and capital is embarked in 

 the mining and transportation of coal, and so many branches of industry 

 depend on it for the successful prosecution of their labours ; while so 

 much of domestic comfort and so mucli of national wealth are, even 

 nom, in the infancy of our mining operations, made to rely on this 

 material; and while steam navigation upon the ocean, and, eventually, 

 that upon our internal waters, must all be performed by its aid, we are 

 warranted in the assertion that few subjects of a practical nature are 

 more deeply and immediately interesting to the public. 



In this view we are snst lined by observing how essentially it has 

 contributed to the power and influence of one of the must commercial 

 nations of the world. The coal deposits ol a small island, which would 

 itself scarcely cover one of the United States, have aflror<led the chief 

 means of carrying her conquests to the remotest parts of the globe. 



Different standards 0/ heating power. 



The heating power of combustibles has, heretofore, been sought to 

 be determined by several dilfereiit methods. 



(1.) The standard proposed by Lavoisier, and adopted by other 

 chemists, was, the weight of ice milled htj the combustion, either in at- 

 mospheric air, or ia pure oxygen gas, of a given weight of the com- 

 bustible body. 



(2.) The standard adopted by Mr. Marcus Bull, who some years 

 since gave to the world a valuable series of experiments on the heating 

 power of wood and coal, was the Unglh of time during ishich a given 

 difference could be maintained between an interior apartment in which 

 combustion was conducted, and an exterior one which was exposed to 

 the cooling effect of the surrounding air, by the consumption of a given 

 weight of each kind of fuel. 



(3.) The mining engineers of Cornwall, and other parts of Great 

 Britain, have formerly used, as a measure of healing power, the weight 

 of water which could be raised one foot high by thi' consumption of a 

 given bulk of coal, when burned under steam boilers which supplied 

 the pumping engines at their mines. 



(4.) The distinguished mining engineer, Berthier, of Paris, pro- 

 f>osed the employment of the oxide of lead as a material from which 

 to obtain oxygen to effect the combustion of different substances, and 

 made the rceight of lead reduced from the state of oxide, by a given 

 weight of each combustible, a standard of its heating power. 



(5.) The German and other European chemists have sought to 

 attain a knowledge of the lieating power of fuel by ascertaining the 

 precise chemical composition of the combustible portion, and thence 

 inferring the weight of oxygen which must enter into chemical com- 

 bination with it during combustion. 



Method here employed. 



None of the above described methods appeared to fulfil the condi- 

 tions required in a practical determination of the evaporative power 

 of the several kinds of coal. Preference was therefore given to that 

 which had, to a limited extent, been employed by Mr. Fyfe, of Edin- 

 burgh ; Mr. Schauf hauti, Messrs. Parkes and Manby, in England ; aTicl 

 by Dr. Dana, Mr. Hayes, and Mr. Francis, in this country. This 

 method consists in burning the coals under a steam boiler, so arrangi'd 

 and furnished with apparatus as to be capable of complete regulation. 

 The water delivered to the boiler, and the coals supplied to the fur- 

 naci», are determined both by weight and measure. 



" The supply of air, the rate of combustion, the pressure and tem- 

 perature of steam, the proportion and character of the products of 

 combustion, both fixed and volatile, whether hft on the grate or pas- 

 sing through the flues, are subject to careful observation and experi- 

 ment. Here, the standard by which we measure the heating power 

 of different coals is the weight of water which a given rueight of each can 

 evaporate from the temperature of 212° Fahrenheit. This standard is 

 probably as constant as any in nature. 



With experiments conducted on this principle, the practice of ge- 

 nerating heat for steam navigation, and for many other useful pur- 

 poses, will be found to correspond in all essential circumstances. 



List of the samples of coals examined. 



The number of samples of coal on which trials of evaporative 

 power have been made, is forty-one. 



01 these, nine were anthracites from Pennsylvania. 



Oi {he free-burning or semi-bituminous coals /;t6/« samples have 

 been tried for evaporative power. 



The next class of coals is that from the bituminom coal fields in the 



neighbourhood of Richmond and Petersburg, in Virginia; of which 

 tltven simples were examined. 



0( foreign bituminous coals six varieties were tried, viz., one 

 from Sydney, Nova Scotia, sent by the Cunard Coal Mining Company ; 

 one of Picton coal, sent by the same ; also, one sample of Scotch, one 

 of Newcastle, one of Liverpool, and one of Picton. 



Two mixtures of anthracite and bilumiuous coal, in certain pro- 

 portions, and two species of coke, (one from the Midlothian coal of 

 Virginia, and the other from Neff's Cumberland coal,) were also tried. 



Tlie mean weight per cubic foot of these artificial cokes, was 

 found to be 32'iJ7 pounds. 



The series of experiments on evaporation was terminated by a 

 single trial of the eH'ct of dry pine wood, of which a quantity had 

 been used daily in heating up tlie apparatus and preparing it for the 

 reception of coal. 



iN'alure of the experiments. 



On each sample of coal were made from one to six trials, accord- 

 ing to the quantity furnished. The coal consumed in one trial never 

 exceeded 15G7 pounds — this being the greatest quantity which the 

 apparatus could receive in the period allotted to each experiment, 

 including (he time requisite for cle.iring out the residua, making the 

 necessarv adjustments, and preparing for a new trial. The total 

 weight of coal consumed in the trials of evaporative power has been 

 nearly ()24 tons; and the weight used, on an average, 978 pounds per 

 trial. This statement may be sufficient to indicate that the experi- 

 ment have been made on a scale unobjectionable on the score of mag- 

 nitude. 



Including the trial of wood, the whole number of experiments oc- 

 cupied 141 days. On each day continuous observations were made 

 during a period averaging from 12 to 14 hours, according to the re- 

 quisitions of the experiment. 



General Characters of the Anthracite Class. 

 The anthracites have specific gravities varying from 1'39 to l-GI ; 

 retain their form when exposed to a heat of ignition, and undergo no 

 proper intumescence while parting with the small portion of volatile 

 matter which they contain ; or, if changed at all, are only disintegrated 

 into angular fragments. Their flame is generally short, of a blue 

 colour, and consequently of little illuminating power. They are ig- 

 nited with difficulty ; give an intense concentrated heat; but generally 

 become extinct while yet a considerable quantity remains unburnt on 

 the grate. 



It appears that the anthracites proper weigh, on an average, 53-35 

 pounds per cubic foot ; and, consequently, require 42 cubic feet of 

 space to stow 1 ton. The natural coke of Virginia requires 48, and 

 the artificial coke from Midlothian and from Cumberland coal an ave- 

 rage of 69-7 cubic feet to accommodate the same weight. The average 

 effect of 1 pound of anthracite was to convert into steam, from water 

 at 212°, 9'5GJ pounds. 



Weight of Cokes compared with Coal. 

 The weight lost by coal in the operation of coking varies according 

 to the various modes in which the operation is effected. The princi- 

 pal methods are as follows : — 



1. By coking in uncovered heaps of coarse lumps, (as at many of 

 the iron works in Great Britain, France, and elsewhere,) and only 

 covering up the ignited mass when flame ceases to be emitted, the 

 loss in weight at Plymouth is stated to be 17, at Pcnn-y-darran 2U, 

 and at Dowlais 34 per cent. This last is, no doubt, far greater than 

 is necessary, owing to the cheapness of coal, and the consequent neg- 

 lect of economy in the management of the coking process. The coals 

 at Dowlais and at Penn-y-darran bear a strong analogy to that of Cum- 

 berland, but have rather less volatile matter. Highly bituminous coals, 

 coked in uncovered heaps, lose from 55 to GO per cent, of their weight, 

 and those of medium quality from 45 to 50, and those of still lower 

 bituminousness from 30 to 40 per cent. In all these cases, a consider- 

 able loss occurs from burning away some portion of the solid carbon 

 on the exterior of the heap, before the slack and cinders are placed 

 upon the coke to extinguish the fire. 



2. By coking in stacks, (that is, in well-covered heaps of coal 

 from 10 to 15 feet in diameter,) as followed in Staffordshire, coals of 

 high bituminousness lose from 50 to 55, and those of a drier nature 

 from 35 to 4i) per cent. 



3. By coking in close ovens, the coal of Rive-de-Gier yields 69 

 per cent, of coke, whereas by the first of the above methods it gives 

 but 45 or 50. In the close oven, the gain of bulk is from 22 to 23 per 

 cent. In the close oven, highly bituminous coals yield from G5 to 66 

 per cent. ; but in the open heap only from 40 to 45, and this with an 

 actual diminution of bulk. 



4. By coking in gas retorts, the Deane coal of Cumberland (Eng- 



32* 



