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TABLE of 30 obfervations of the fame nature made in 

 the winter months. 



There can aiife no dotibt but that heat is extricateti by 

 comprcfTion from atmofphcric air ; and that it is further pro- 

 bable, that the quantity of heat diftngagud is in proportion 

 to its condeiifation. If, therefore, we are allowed to reafon 

 upon this fubjeft, we (liould thite the following as a confide- 

 rable approximation towards truth. It is univcrfally believed 

 ar.d ftlt, that combuflion in the blaft furnace in June, July, 

 and Angnft, is confiderably diininifhed, as a confequence of 

 the incrcaftd temperature of the air. The metal, in thefe 

 months, is frequently debafcd in point of carbonation, and 

 diminifhed nearly one half in point of quantity. We fhall 

 fiippofe that this takes place at a temperature of 100, which 

 has been proved to exiil imder a preffure of 21 pounds. The 

 reverfe of this happens in the cool fcafon of the year, and 

 particularlv in the winter months. The furnace then yields 

 the largcll quantity of iron, and in the moll profitable man- 

 ner. Tliis, with the fame probability, talces place at a 

 temptratnrt ot ^c found in the table. 



It would therefore appear to refult from thefe, that two 

 thirds, or one half of the iron only, is manufactured at a 

 temperature of J 00, than in winter at 50. The difference 

 between thefe degrees of temperature amounts to 50, and 

 mod probably in combuflion afledls the operation as fenfibly 



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as the huT.an frame is affefted by a tranfition of temperature 

 equal or fimilar. It is not neceftary now to Hate the difler- 

 ence between fummer and the denfer air of our winter, the 

 circumllances of evaporation and aqueous folution ; thefe 

 fhall be particularly attended to in the general proccfs of 

 manufafluring iron. The great difference of temperature 

 orifing fiinply from comprefQon feems to us adequate to ex- 

 plain many phenomena regarding the blaft furnace. Our 

 knowledge, however, upon this fubjeft can only be for- 

 warded by a general colleftiou of fafts well afcertained, 

 {hewing what are the various degrees of heat made fenfible 

 by the comprcfTion of the blowing machine under every den- 

 fity ; what the difference in temperature, the denfities being 

 alike, when tlie air is received over water, in the air-vault, 

 or in the regulating cylinder. From thefe it might mod 

 probably refult, that the higher the denfity of the air, the 

 greater would be the degree of heat manifcilcd ; and it might 

 alfo follow, that in the ratio of this denfity, or temperature, 

 when the air was received over water, fo would be the eva- 

 poration or quantity of water fufpended in the air, and of 

 courfe difcharged into the furnace. 



This article may be concluded by the following remarks : 

 — Ttiat all iron works are not alike afleited by the heat of 

 the fummer months. Many iron works prefervc the qua- 

 lity of the iron, though at the expence of fuel, and with 

 lofs of quantity ; but at other places no extra quantity 

 of fuel will compenfate, either as to quality or quantity, for 

 the want of cool air. Neither fituation nor denlity of blall 

 will explain this curious circumdance ; for with blafls of 

 equal denfity and quantity, works fituated not 50 feet above 

 the level of the fea have been found to manufacture a greater 

 quantity of foft iron in fummer, than at a fimilar work, not 

 ten miles diflant, fituated at leall 250 feet higher. At both 

 of thefe works the air is received over water; and no material 

 alteration in the ufe of that air is or can poffibly be applied. 

 The caufcs of this difference mufl be fought for in the na- 

 ture of the coal and iron-ftone ufed at both works, the in- 

 vefligation of which, however interefling, would prove a 

 mofl laborious undertaking. 



Blast Furnace, a large conical or quadrangular building 

 ufed at iron-works for fiuelting iron-Hones and ores. 

 Blast Furnace, Defcriplion of. 



Plate {Chcmi/lry) W. fg. I. reprefents a blall furnace, and 

 part of the b'owmg machine conflrutted upon what at one 

 time was the general plan at ii'on-works. 



A, the regulating cylinder, eight feet in diameter, and 

 eight feet high. B, the floating piflon loaded with weights 

 proportioned to the power of the machine. C, the valve by 

 which the air is paffed from the pumping cylinder into the 

 regulator ; its length 26 inches, and breadth 1 1 inches. D, 

 the aperture by whicli the blafl is forced into the furnace. 

 Diameter of this range of pipes 18 inches. The wider thefe 

 pipes can be with convenience ufed, the lefs is the friclion, and 

 the more powerful are the efftfts of the blaft. E, the blow- 

 ing or pumping cylinder, fix feet diameter, and nine feet 

 high ; travel of the pifton in this cyli\ider from 5 to 7 feet 

 per flroke. F, the blowing pillon, and a view of one of the 

 valves, of whicli there art fometimes two, and fometimes 

 four, dillribnted over the furface of the pillon. The area 

 of each is proportioned to the number of valves, commonly 

 they are 12 — 16. G, a pile of folid ftone building, on 

 which the regulating cylinder refts, and to which the flanch 

 and ftilts of the blowing cylinder are attached. H, the 

 fafety valve, or cock, by the fimple turning of which the 

 blail may be admitted to or fliut from the furnace, and paffed 

 off by a collateral tube on the oppofite fide. I, the tuyere 



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