B L O 



B L O 



Air-vaults were conftrufted both at the Clyde and Muir- 

 kii'k iron works in Scotland, and a conftaut current of air 

 produced ; but nearly one half the quantity lifted bv the air- 

 pump efcaped through the walls and arches of the building. 

 This was at any time made vifible by rubbing foapy water 

 upon the external walls. 



At Devon iron works in Scotland, an air-vaulf was ex- 

 cavated from the folid rock, 72 feet long, 14 feet wide, 

 and Ij feet high ; equal to 13,000 feet of cubical meafure- 

 ment. This ijnmenfe excavation was made comparatively 

 air-tight, by cauking the feams and fiffures of the rock, 

 plailering and then covering the whole with alternate layers 

 of pitch and elofe wove paper. 



This was the n'ofi: perfeft experiment ever tried upon 

 the air-vault ; and if an opinion is to be formed of the 

 perfeiflion of the apparatus by the quantity of iron at 

 one time manufactured, a very trifling portion of air in- 

 deed mud have been loft. 



It has been frequently noticed in Scotland, that at works 

 where the materials were in any degree fimilar, 3000 

 to ,5500 cubical feet of air per minute will, in the courfe of a 

 week, produce from 30 to 35 tons of pig iron, whatever may 

 be the denfity at which it is thrown into the furnace. 



The Devon furnace at one time averaged 33 tons weekly 

 for 9 months running, and confumed of air, per data fur- 

 tiifhed by Mr. Roebuck in his paper publifhed in Nicholfon's 

 Journal, vol. iv. nearly 340c cubical feet per minute, under 

 a preffure of 2|- lbs. per fquare inch. Notwithltanding 

 this powerful demonftration, ilrong prejudices were enter- 

 tained to its difadvantage ; and many behcved, that had any 

 other mode of regulator been attached to the blowing ma- 

 chine, abundance of air would have been obtained to have 

 blown two furnaces equally well. That this idea was incor- 

 reft, may be eafily gathered by calculation from the area of 

 the air-pump, the length of the working ftroke, and the 

 number of ftrokes per minute, all of which are particularly 

 ftated by Mr. Roebuck. 



For the general conftruflion of an air-vault formed by 

 building, fee Plate XV. {Chemljlry.) 



Fig. I . is a fe£lion of the vault conftrufted under the 

 bridge-houfe, or place where the materials are proportioned, 

 previouily to their being thrown into the furnace. One half 

 a blafl furnace outline, is feen as connected in point of fitiia- 

 tion and blaft to the air magazine. 



A, the termination of the blaft pipes that convey the air 

 from the blowing cylinder into the receiver, 3 feet diameter ; 

 the length depends upon the contiguity of the engine to the 

 vault. 



B B B B, four vaults, i,j feet wide each, 25 feet deep, 

 and 10, XI, 12, and 13 feet high to the fpringing of the 

 arches ; total height to the crown of the arches, 165, 17I, 

 i8|, and 195 feet. Thefe cells communicate with each 

 other by arched openings in the crofs-walls, which may be 

 dillinftly feen in the ground plan at L. 



C C, the eduftion pipes that carry the air to the furnace ; 

 18 inches diameter. 



D, end view of the range of laying pipes at the tuyere of 

 the furnace. The dotted lines betwixt D and C are meant 

 to reprefent the horizontal range of the pipes. 



E, part of the outline of a blaft furnace to fltew its pro- 

 per fituation to the air vault. 



F F F F, floor of the refpeftive vaults, compofed of a 

 mixture of two parts of boring dull, two of fine riddled 

 lime, aud one part of fine roafted iron flone, mixed up iuto 



plafter with water tontaining a confiderable portion of 

 fait. 



G G, end walls of bricks or ftone, four feet thick. 



H H H, lining of brick-work, built in the moft acciJ* 

 rate manner, with fine riddled mortar, and run every fecond 

 or third courfe with mortar made thin and very liquid. 

 Thefe walls are two feet and a half in thicknefs, are care- 

 fully plartered, and afterwards covered with feveral layers 

 of ftrong paper and pitch, to prevent the efcape of air. The 

 roofs of the vaults are finifhed in the fame manner. 



I, door arch into the vaults ; entrance obtained by means 

 of a ladder or wooden ftairs fufpended within. 



K, fpace above the arches, filled with rubbifh, to prevent 

 any fpring, and to raife the floor to the level of the 

 furnace top. 



L, the range of the floor, or acclivity to the furnace 

 mouth. 



Fig. 2. is a ground plan of the bridge-houfe containing 

 the air-vaults, and exhibits one half the ground plan of the 

 furnace through the centre of the tuyere arches. 



B B B B, correfponding to the fame letters in the ele- 

 vation. 



C C, pipes for taking off the blaft; into the furnace. 



D, correfponding to the fame letter in the feftion. 



E, main pillar of the furnace, fame as E in the feclion. 

 GGGG, and H H H, correfpond with the fame letter* 



in the elevation. 



I, fquare for receiving the furnace hearth. 



K, part of the ground view of the hearth, and the ap- 

 proaching blaft pipes. 



L L L, openings of the crofs arches, which communicate 

 the vaults with each other. 



Tlie cubical contents of a vault, conftrufted according 

 to thefe dimenfions, will amount to 20,000 feet. 



In general, it may be remarked upon the conftruftion of 

 the blowing machine, that fince the period of the intro- 

 duftiou of Mr. Watt's engine, the air-pump, or blowing cy- 

 linder, has been conftrnfted fo as to difcharge a cylinder full 

 of air every afcent and defcent of the pifton. This, inftead 

 of travelling 4 to 5 feet per ftroke, more generally moves S 

 feet ; and the number of cylinders per minute are feldom 

 under 24. 



Formerly, in the common atmofpheric engine, the move- 

 ment of the pifton from top to bottom, and back again, 

 produced only one cylinder full of air from the air-pump, 

 and the number of cylinders dlfcharged per minute feldom 

 exceeded 16. A fteam cylinder of 40 to 44 inches diame- 

 ter, and an air-pump of 6 feet diameter, the pifton moving 

 about 5 feet per ftroke, were deemed fufncient in the con- 

 ftruftion of a blowing machine for two blaft furnaces. The 

 quantity of air pumped up and thrown into the furnaces by 

 fuch an engine feldom exceeded 3000 cubical feet per mi- 

 nute. This, and even a larger quantity, is now thrown into 

 one furnace, and the produce by fuch means increafed frora 

 15 to 3 J tons weekly. 



The firft fet of tables following are calculated to fliew 

 the quantity of air that would be difcharged by blowing 

 cylinders of various diameters, the length and number of the 

 ftrokes being given. 



The fecond fet, to fhew what diameter of blowing cyJin- 

 der is requifite, with a given fteam power, to raife the air to 

 a certain denfity per fquare inch. See Engine, Water 

 Reculatorj and Hegulatinc Vavlt. 



TABLE 



