1840.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



423 



Faraday and Mr. Stodflart) ; aiid Mr. Pepys liaving obligingly sujiplied Capt. 

 Johnson ^\'ith specimens of similar kinds of steel lo those used by them, these 

 examples, together with pivots made of the ordinary kind of steel, and har- 

 dened and tempered in the manner recommended by eminent instrument- 

 makers, were placed in a frame for experiment ; and to these again Captain 

 Johnson added certain contrivances of his own, such as rubbing a steel pivot 

 with sal-ammoniac, then dipping it into zinc in a state of fusion, and after- 

 wards changing the extreme point. Some specimens he coated with a mix- 

 ture of powdered zinc, oil of tar, and turjieutine ; and others again were set 

 in zinc pillars, having small zinc caps, through which the extreme point of 

 the pivot protnided after the manner of black lead through pencil tubes. 

 The whole of the specimens were then placed in a cellar, occasionally exposed 

 to the open air, examined from time to time during more than half a year, 

 and their several states, as respected oxidation, duly registered. Without 

 going into the details of this register, the general result was, that not any of 

 the kinds of steel pivots used in this trial, except such as were coated with 

 zinc, remained free from rust, while the ])ivot made of the "native alloy'' 

 which is found with platinum, completely retained its brilliancy. Captain 

 Johnson then applied a more severe test to this singular substance, first, by 

 placing sulphuric acid, and then nitio-muriatic acid upon it ; but even under 

 this trial he could not observe that any change had been effected, although 

 the blade of a penknife, subjected to a similar process, was rusted to the cen- 

 tre. Having enumerated the facts respecting the trials to which he had sub- 

 jected this curious material, Capt. Johnson stated the conclusion that he had 

 come to, namely, that it is sufficiently tough not to break, and hard enough 

 not to bend, under the trials to which it would he fairly exposed; and that 

 being alike free from magnetic properties and liability to oxidation from ex- 

 posure to the atmosphere, it possesses the requisite {pialities for the iiivot of 

 the mariner's compass ; and he could not but anticipate that, when fitted 

 with a ruby cap to cori'espond, it would lie found greatly to improve the 

 working. Besides the application of this substance for compass pivots, Capt. 

 Johnson stated that it might probably be found advantageous for other in- 

 struments, and especially for the points of the axes of the dipping needles 

 fitted, on Mr. Fox's plan, for use on board ship. 



Mr. Hawkins has used this "native alloy" for several years in tipping the 

 points of pens, and not a single instance exists of any of these pens showing 

 the least symptom of wear. He tried native alloy on a cap, in comparison 

 with ruby, when he found that in the same circumstances, the ruby was 

 ground away with diamond dust twice as rapidly as the native alloy. He had 

 made engravers' tools of the same metal, and when made too sharp they can- 

 not be blunted on the Turkey stone, but only by diamond dust.— Su- J. 

 Kohison could bear testimony to one of Mr. Hawkins's pens, which he had 

 used for years, not being at all changed. — Mr. Hawkins stated that this alloy 

 consists of native crystals of osmium and iridium in conjunction with plati- 

 num. 



Mr. Lang " On an Improvement on the Air Pump." A letter from this 

 gentleman was read, but from some mistake, the paper itself had not been 

 received. 



INSTITUTION OF CIVIL ENGINEERS. 



" On the Properties and Chemical Constitution of Coal, with Remarks on 

 the ]\/ethods of increasing its Calorific Effect, and prevent iuf/ the Loss which 

 occurs duririrj its Combustion." By Charles Hood, F.R.A.S., &c. 



It appears that, previous even to the invasion of the Romans, coal was 

 used as a fuel in Great Britain ; but such was the prejudice against it, that 

 wood was the fuel generally in use among the higher classes until the 

 eighteenth century, when the supply of it diminished so considerably as to 

 render necessaiT the substitution of coal ; and from that time the increase in 

 its consumption has been immense. 



Previously to the seventeenth century, the smelting of iron and all other 

 metals was performed by charcoal ; but the attempts of Sturtevant and Ra- 

 venson in 1612-13, and of Dudley in 1619, to introduce the use of coal or 

 coke in blast furnaces having proved the possibility of success, the progress 

 of the innovation, though slow, was certain, and led to the transfer of the 

 iron works from many of the original positions in the midst of forests to the 

 coal districts where they are now placed. 



The author considers his subject under three heads :— -1st, The chemical 

 character and composition of coal ; 2ndly, Its properties as a combustible ; 

 and 3dly, The nature and application of its various gaseous products. 



1st. The opinion that coal is a compound of carbon and bitumen has been 

 objected to by some chemists, on the gi'ound that Ijy no process hitherto 

 pursued in analyses has it been possible to resolve it entirely into these two 

 substances ; even at a low temperature a quantity of gaseous matter is thrown 

 oif, and at an elevated degree of heat an evident decomposition of the bitu- 

 men takes place. Even anthracite contains a small portion of volatile matter, 

 its coniiionent parts being carbon, oxygen, hydrogen, and nitrogen; the hy- 

 drogen being either combined with the oxygen to form water, or with a 

 small portion of carbon to form carburetted hydrogen, which exists in a 

 gaseous state in the pores of the coal. In bituminous coal, the hydrogen is 

 combined with a larger proportion of oxygen and nitrogen ; the mechanical 

 difference being, that the bituminous and free-burning coals (more particu- 

 larly) melt by heat when the bitumen reaches the boiling point, whereas 



anthracite is not fusible, nor will it change its form, until it is exposed to a 

 much higher degree of temperature. 



Two tables of the analyses of different coals are given from the authorities 

 of Jfuslict, Thomson, Vannxem, Daniel], Ure, aud Keynault ; No. 1 showing 

 the proportions of carbon, ashes, and volatile matter, with the specific gravity 

 of the coal and of the coke ; and No. 2 showing the proportions of carbon, 

 hydrogen, azote, and oxygen. These tables show that the lai-gest quantity of 

 carbon (92'87) is contained in llie Kilkenny anthracite, and the least quan- 

 tity (61-72) in Cannel coal ; and that the nature of the volatile matter greatly 

 afi'ects the quantity of coliC — the aggregate quantity of the gaseous products 

 of coking, splint, and cherry coal, being very nearly similar; while the quan- 

 tity of coke obtained from these different species varies more than 45 per 

 cent. 



The author then points out the continual presence of azote, which quits 

 the base with the greatest difficulty ; and also the affinity of sul])hu]', not 

 only for the coal, but for the coke, as it is rarely found to have been com- 

 pletely expelled, even from the most jierfectly made coke ; the only coal 

 found to be even partially free from it being anthracite, in some species of 

 which no traces of its presence are found. 



2dly. The application of coal as a fuel depends on the chemical change 

 which it undergoes in uniting, by the agency of heat, mth some body for 

 which it possesses a powerful affinity. In all ordinary ease? this effect is 

 produced by its union with oxygen. AThen coal is entirely consumed, the 

 carbon is wholly converted into carbonic acid gas and carbonic oxide, and 

 the hydrogen into water in a state of vapour. The atmosphere supplies the 

 necessai-y oxygen for this puqjosc ; and in this state the products of the com- 

 bination are nearly or quite invisible, both of them being almost colourless 

 fluids ; if, therefore, any smoke be visible, it is the result of imperfect com- 

 bustion. Some calculations are given to ascertain the amount of loss that is 

 sustained when the smoke escapes unconsumed; from which it appears, that 

 with bituminous coal about 37 or 38 per cent, more heat is produced when 

 the smoke is consumed than when it escapes freely. Many modes of con- 

 suming smoke have been attempted ; those which appear to have been at- 

 tended with the greatest success are — 1st. Causing the smoke from the fresh 

 coals to pass through or over that portion of the fuel which is more perfectly 

 ignited; 2dly. Supplying heated air to the top of the fuel, as well as admit- 

 ting cold air through the ash-pit in the usual manner; and 3dly, Throwing 

 a jet of steam into the furnace or into the chimney. The various modes of 

 earning into effect these plans are briefly alhuled to ; from them a few may 

 be selected. Robertson's plan was to use inclined furnace bars, where the 

 fresh coals were placed close to the fire-door, and lieing there partially car- 

 bonized, gave out the gas, which, in passing over the mass of incandescent 

 fuel, was ignited, and became active flame, thus economizing fuel aud pre- 

 venting smoke. In this and similar cases, by the slow distillation of the coal, 

 a gas is jiroduced, which not only inflames at a lower temperature than the 

 dense defiant gas produced by rapid distillation, but which only requires for 

 its combustion a quantity of oxygen never exceeding double its own volume, 

 or ten times its bulk of atmosjilieric air, wliile defiant gas requires three 

 times its own volinne of oxygen, or fifteen times its bulk of atmospheric air. 

 The elimination of a gas which burns with so small a portion of oxygen is, 

 therefore, the principal cause of the non-production of smoke in furnaces of 

 this description. The second mode of consuming smoke is founded on the 

 necessity which exists for a large supply of air being requisite to inflame the 

 gases given oflT from coal by a rapid and intense heat ; and this is accom- 

 plished by introducing a qiiantity of heated air above the burning fuel. When 

 a qua)itity of fuel is thrown into a funiace, the increased thickness of the 

 mass opposes additional resistance to the passage of air through the bars ; 

 the temperature of the furnace is lowered, and an increased volume of gas is 

 at the same time given out. If at this moment a quantity of air, heated to 

 the temperature of the gas, be admitted, the gas immediately inflames, and 

 that which would have produced a dense black smoke passes oft' in the in- 

 visible state of carbonic acid gas and vapour of water. Different gases re- 

 quire dift'erent degrees of heat to inflame them ; and this explains the easy 

 combustibility of the volatile products of coal when the heat is so managed 

 as to produce those gases which inflame at the lowest temperature. A larger 

 quantity of air is required at the time that the coal is first thrown on than at 

 a subsequent period ; therefore, when economy is studied, the supply of air 

 should be gradually diminished as the mass approaches an incandescent state. 

 The use of heated air has produced most important results in the manufacture 

 of iron with bituminous coal, and also with anthracite; the latter fuel having 

 been almost neglected until the recent application of this principle of era- 

 ploying heated air to promote its combustion, although it is known to be 

 capable of producing perhaps a more intense heat than any other carbo- 

 naceous fuel. The rationale of the third plan of consuming smoke by in- 

 jecting a jet of steam into the fire or the chimney, is less obvious than the 

 others. In 1805, Mr. Danes Gilbert observed, that whenever the waste 

 steam of one of Trevithick's engines was permitted to escape into the chim- 

 ney, the smoke from the coal was rendered invisible. Subsequent expeii- 

 ments confirmed this fact; and it was supposed that the steam, being 

 decomposed, furnished oxygen to support combustion. The author combats 

 this opinion, and accounts for the efl'ect by the increased draught of the 

 furnace caused by the jet of steam into the chimney, by which means a larger 

 portion of air is brought into contact with the burning fuel ; thus supplying 

 the previous deficiency of oxygen to the fire, and promoting the combustion. 

 As steam is only about half the weight of air at a like temperature, and the 



