132 



ON MAMNE BOILERS. 



1855.] 



sary to form carbouie acii.1 combines with carbon, the result 

 will be carbonic oxide, a product of imperfect combustion. A 

 certain supply of atmospheric air, therefore, is necessary ; but 

 this supply may be too copious or too scant ; it may enter the 

 furnace too rapidly or too slow ; but it cannot be too high for 

 rapid combustion. It is also evident that the quality of the 

 fuel must have a controlling influence upon these various con- 

 ditions. Wood as fuel for marine boilers is out of the ques- 

 tion ; we can only consider minei'al coals, anthracite and bitu- 

 minous, as fit for ocean steaming. It is not my intention here 

 to analyse these varieties ; I only notice them in so far as their 

 peculiar qualities require peculiar mechanical arrangements for 

 good combustion. 



Soft or bituminous coal requires more time to be consumed 

 economically than hard coal. The large bulk of hydrogenic 

 and bituminous compounds, mixed up with floating particles of 

 carbon, which resvilt from the burning of soft coal, require to 

 be thoroughly mixed with heated air before perfect combustion 

 can take place. The mechanical arrangements to efTeot this 

 are of great importance, but may be overlooked when hard or 

 anthracite coal is consumed. The fuel admits of a much more 

 rapid consumption and of a powerful blast, while the draught 

 of a soft coal furnace should not be very strong. 



Experience has not yet settled the most economical speed of 

 consumption of mineral coals. Watt's rule was to allow one 

 superficial foot of grate surface for every ten superficial feet of 

 heating surface ; and tbis rule produces good results with 

 natural draughts. The boilers of the Collins' steamers are 

 undoubtedly the most eflicient and best constructed boilers 

 now in use, either here or in Europe. According to Mr. Isher- 

 wood, those of the Arctic contain 0.357 feet of grate for 11-84 

 feet of heating surface for eveiy efieotive horse-power, or 33 

 feet of heating surface for one foot of grate. 



According to the same author, whose account of the per- 

 formance of the Arctic, published in the " Journal of the 

 Franklin Institute," appears to be reliable, the aver-ige con- 

 sumption of anthracite during six trips was 7,980 lbs. per hour. 

 The aggregate grate surface of the four boilers of that steamer 

 is 588 feet, which gives 13-57 lbs. of coal per bour for each 

 foot of grate. In boilers of ordinary construction with natural 

 draught, half the weight of soft coal would be a fair consump- 

 tion. 



Chemists who have examined the evaporative power of vari- 

 ous fuels agree that one pound of good mineral coal, perfect^ 

 consumed, will evaporate over 11 lbs. of boiling -water. Exjje- 

 riments on a larger scale will seldom evaporate more than 9 lbs. 

 to 10 lbs. The boilers of the Arctic, during those six trips, 

 evaporated 7'Hbs. of steam from water of 110° by lib. of 

 anthracite ; and this is one of the highest results that has 

 been obtained in the regular working of marine boilers. It ij 

 evident, therefore, that there is room left for improvements. 

 There is still a waste of fuel in the Collins' steamers, which 

 arises from imperfect combustion ; the result in part of a 

 faulty construction ; and, no doubt, in part is attributable to 

 imperfect stoking. Much, of course, depends upon the mode 

 of firing ; nor is it always practicable to carry on this impor- 

 tant part of the service according to the best rules. 



In attempting to improve the construction of boilers, we 

 may receive good hints from an examination of the condition 

 and working of other furnaces, in which good combustion and 

 a higb degree of heat ai'e important objects. Furnaces used 



in the manufacture of iron, such as blast, puddling, heating, 

 and annealing furnaces, may be refen-ed to. 



Perfect combustion can only take place under sucb circum- 

 stances as are favorable to the development of intense flame 

 and heat. Aside from the neces.sary quantity of air supplied 

 at a certain rate, and heat if possible, there are other contin- 

 gencies upon which success depends : a very important one is 

 the nature of the material which surrounds the lurnace, forms 

 its walls and roof, and comes into immediate contact with the 

 fire. The question then at once arises, can the process of 

 combustion be successfully carried on in a narrow furnace, sur- 

 rounded by iron walls and roof, in contact with water, which 

 absorbs the heat at a rapid rate? Most certainly not. Who 

 would undertake to heat and puddle iron in a furnace built 

 of iron plate in contact with water ? Iron water-boshes are 

 sometimes resorted to ; but they have a tendency to retard the 

 process, and should be avoided if possible. Such furnaces are 

 constructed of good fire-brick, which is a slow-absorbing and 

 slow-conducting material, and after being glazed over by the 

 strong heat will strongly reflect it. By this strong reflection 

 and non-absorption the process of combustion is supported in 

 an eminent degree ; so much so, that a degree of heat is ob- 

 tained far exceeding the temperature of any boiler furnace. 

 As little heat as possible should be absorbed by the walls or 

 roof of a boiler furnace ; every endeavour should be made to 

 reflect and concentrate the fire. Imperfect combustion in any 

 furnace most generally arises from the fact that the heat is not 

 allowed to accumulate and concentrate. The sole object of a 

 boiler furnace should be to favour combustion, and to develop 

 flame and blaze; and this can only be accomplished under the 

 influence of a highly concentrated and excited action. The 

 caloric stream thus fully elaborated, on leaving the furnace, is 

 then allowed to expand itself ; and to be absorbed by the sur- 

 face of the boiler. 



I may remark here, by way of general comment upon furnaces 

 for heating houses, that the whole tribe of patent furnaces with 

 which the country is blessed have all, more or less, grown out of 

 erroneous notions, and are the oflspring of profound ignorance 

 of the laws of combustion and of heat. Aside from the vitiated 

 air they supply, they are all wasting fuel at an enormous rate. 

 This subject is better understood in the north of Europe, 

 where long winters and scarcity of fuel have taught men to 

 build furnaces on correct principles. 



The temperature of a puddling or heating furnace has to be 

 raised to about 3,000° : this can only be accomplished under 

 the reflecting and reverbatory action of the walls and roof. A 

 concentrated blast may produce a greater heat at a certain 

 point, but it will not be diffused. Under the above circum- 

 stances, and by means of strong blast, from three to four times 

 as much fuel may be consumed on the same surface of grate in 

 in one unit of time as can be accomplished in a common boiler 

 furnace. In a well-constructed heating furnace at my rolling- 

 mill at Trenton, N. J., 8,000 lbs. of anthracite are consumed 

 in ten hours for the heating of 18,000 lbs. of charcoal hammered 

 blooms, on a grate of twenty superficial feet, which is equivalent 

 to 40 lbs. per hour on one foot of grate. This cannot be ac- 

 complished in the furnaces of the Collin's steamers, which con- 

 sume 13^ lbs. per hour to one foot of grate. 



In the above a principle is delineated which to my know- 

 ledge has been entirely overlooked, and which must be satisfied 

 before we can attain much higher results. 



Another glaring defect in all marine boilers, thc^e of the 



