Feb. 3, 18S1 



NA TURE 



327 



the electric arc possesses advantages unrivalled by any other 

 knowii source of heat. 



Carbonaceous material such as as coal or woid is practically 

 inert to oxygen at ordinary temperatures ; but if wood is heated 

 to 295° C. (593° F.), or coal to 326° C. (617" F.), according to 

 experiments by M. Marbach, combination takes place between 

 the fuel and the oxygen of the atmosphere, giving rise to the 

 phenomenon of combustion. It is not necessary to raise the 

 whole of the combustible materials to thi, temperature in order 

 to continue the action ; the very act of combustion when once 

 commenced gives rise to a great developaient of heat, more 

 than sufficient to prepare additional carbonaceous matter, and 

 additional air for entering into combination ; thus a match 

 suffices to ignite a shaving, and that in its turn to set fire to a 

 building. 



The first effect of combustion is therefore to heat the com- 

 bustible and the air necessary to sustain combustion to the tem- 

 perature of ignition, but in dealing with the combustible called 

 coal other preparatory work has to be accomplished besides 

 mere heating in order to sustain combustion. The following is 

 an analysis from Dr. Percy's work on "Fuel" of a coal from 

 the Newcastle district : — 



Carbon 81 '41 Nitrogen 2'05 



Hydrogen ... 5'83 Sulphur 074 



Oxygen ... .. 7'90 Ash.. 2'o7 



which shows at a glince that nearly 16 per cent, of the total 

 weight consists of such permanent gases as hydrogen, oxygen, 

 and nitrogen. These gases are partly occluded or absorbed 

 within the coal, but are also combined with carbon-forming 

 volatile compounds, such as the hydrocarbons and ammonia, so 

 that v\hen coal is subjected to heat in a closed retort, as much as 

 35 per cent, passes away from tlie retort in a gaseous condition 

 and as vapour of water, partly to condense again in the form of 

 tar, and of ammoniacal liquor, and partly to pass into the gas 

 mains as illuminating gas, a mixture mainly of marsh gas (ChJ, 

 olefiant gas (C^IIj), and acetylene (CoHg), its value as an iUu- 

 minant depending upon the percentage of the last two constitu- 

 ents rich in carbon. The result of the distillition of a ton of 

 coal will be as follows, from data with which Mr. A. Upward 

 has kindly supplied me : — 



Coke 



Tar 



Ammoniacal Liquor 



Gas 



Carbonic acid 



Sulphur removed by purifying 



Loss 



13-60 



I '20 



31S 

 o-i8 

 0-30 



0'12 



So great is the loss of heat sustained in an ordinary coal fire, in 

 consequence of the internal work of volatilisation, that such a 

 fire is scarcely applicable for the production of intense degrees 

 of heat, and it has been found necessary to deprive the coal in 

 the first place of its volatile constituents (to convert it into 

 coke) in order to make it suitable for the blast furnace, for 

 steel melting, and for many other purposes where a clear intense 

 heat is required. 



In the ordinary coke oven the whole of the volatile con- 

 stituents are lost, and each 100 lbs. of coal yield only 66 lbs. of 

 coke, including the whole of the earthy constituents which on 

 a large average may tie taken at 6 lbs., leaving a balance of 

 60 lbs. of solid carbon. In burning these 60 lbs. of pure 

 carbon, 220 lbs. of carbonic anhydride (CO™) are produced, and 

 in this combination 60 x 14,500-870,000 heat units (according 

 to accurate determinations by Favre and Silbermann, Dulong, 

 and Andrews) are produced. 



The 34 percent, of volatile matter driven ofl" yield, when the 

 condensible vapours of water, ammonia, and tar are separated, 

 about 16 lbs. of pure combustible gas (being equal to about 

 I0,ooo cubic feet per ton of coal), which in combustion produce 

 16x22,000 = 352,000 heat units. The e cape of these gases 

 from the coke oven constitutes a very serious loss, which may 

 be saved, to a great extent at least, if the decarburisation is 

 .effected in retorts. The total heat producible from each 

 100 lbs. of coal is in that ca-e 870,000 + 352,000= 1,222,000 or 

 12,220 units per lb. of coal. Deduc'.ion must, however, be 

 made from this for the heat required to volatilise 34 lbs. of 

 volatile matter for every 100 lb;, of coal used, and also for 

 heating the coke to redness, or say to 1000° F. Considering 

 the multiplicity of gases and vapours produced it would be 



tedious to give the details of this calculation, the result of 

 which would approximate to 60,000 heat units, or 600 units 

 per lb. of coal treated. 



We thus arrive at 12,200-600=11,600 heat units as the 

 maximum result to be obtained from i lb. of best coal. Con- 

 sidering, however, that the coal commonly used for industrial 

 purposes contains more ashes and more water than has been 

 here assumed, a reduction of say 10 per cent, is necessary, and 

 the calorific power of ordinary coal may fairly be taken at 

 10,500 units per. lb. 



In applying this standard of efficiency to actual practice 

 it will be found that the margin for improvement is large 

 indeed. Thus in our best steam-engine practice we obtain one 

 actual HP. with an expenditure of 2 lbs. of coal per hour (the 

 best results on record being 1-5 lb. of coal per Indicated HP.) A 

 HP. represents 33,000 x 60= 1,980,000 foot-lbs. per hour, which 



is — — '- = 990,000 foot-lbs., or units of force, per lb. of fuel. 



Dr. Joule has shown us that 772 foot-lbs. represent one unit of 



heat, and i lb. of coal therefore produces 



990,000 

 772 



= 12S2 units 



of heat instead of 10,500, or only one-eighth part of the utmost 

 possible result. 



In melting steel in pots in the old-fashioned way, as still 

 practised Largely at Sheffield, 25 tons of best Durham coke are 

 consumed per ton of cast steel produced. The latent and 

 sensible Iieat really absorbed in a pound of steel in the opera- 

 tion, does nut exceed 1800 uniis, whereas •z\ lbs. of coke are 

 capable of producing 13,050 x 2'5 = 32,625 unit-s, or 18 times the 

 amount actually utiUsed. 



In domestic economy the waste of fuel is also exceedingly 

 great, but it is not easy to give precise figures representing the 

 loss of effect, owing to the m.anifold purposes to be accomplished, 

 including cooking and the heating and ventilation of apart- 

 ments. If ventilation could be neglected, close stoves such as 

 are used in Russia would unquestionably furnish the most 

 eonomical mode of heating our apartments ; but health and 

 comfort are after all of greater importance ihan economy, and 

 these are best secured by means of an open chimney. Not only 

 does the open chimney give rise to an active circulation of air 

 through the room, which is a necessity for our well-being, but 

 heat is supplied to the room by radiation from the incandescent 

 mrterial instead of by conduction from stove surfaces; in the 

 one case the walls and furniture of the room absorb the luminous 

 heat rays, and yield them back to the transparent air, whereas, 

 in the latter case, the air is the first recipient of the stove heat, 

 and the walls of the room remain comparatively cold and damp, 

 giving ri-e to an unpleasant musty atmosphere, and to dry rot 

 or other mouldy growth. The adver-aries of the open fire- 

 place say that it warms you on only one side, but this one-sided 

 radiant heat produces upon the denizens of this somewhat humid 

 countr}', and indeed upon all unprejudiced people, a particularly 

 agreeable sensition ; which is proof I think of its healthful in- 

 fluence. The hot radiant fire imitates indeed the sun in its 

 effect on man and matter, and before discarding it on the score 

 of wastefulness and smokiness, we should try hard, I think, to 

 cure it of its admitted imperfections. 



If incandescent coke is the main source of radiant heat, why, 

 it may be asked, do we not resort at once to cDke for our 

 domestic fuel ? The reasons are twofold : the coke would be 

 most difficult to light, and when lighted would look cheerless 

 without the lively flickering flame. 



The true solution consists, I venture to submit, in the com- 

 bination of solid and gaseous fuel when brought thoroughly 

 under control, by first separating these two constituents of coal. 

 I am bold enough to go so far as to say that raw coal should not 

 be used as fuel for any purpose whatsoever, and that the first 

 step toward the judicious and economic production of heat is 

 the gas retort or gas producer, in which coal is converted 

 either entirely into gas, or into gas and coke, as is the case at 

 our ordinary gas works. 



When in the early pait of the present winter London was 

 visited by one of its densest fogs, many minds were directed 

 tiwards finding a remedy for such a state of things. In my 

 own case it has resulted in an arrangement which has met with 

 a considerable amount of favour and practical success, and I do 

 not hesitate to recommend it to yon also for adoption. Its 

 general application would, as regards dwelling-houses, make 

 our tow n atmosphere as clear as that of the surrounding country. 

 If it can be shown that the arrangement nay be easily and 



