BLO 



618 



BOA 



Blowing 

 Engine. 



the engine. The air above the piston will obviously 

 be condensed, and forcing open the hanging valves in 

 the neck G, will rush through them into the pipe 

 L, and thence into the receiver O P. While the 

 piston thus rises and condenses the air above it, there 

 is a vacuum below the piston, and the external air 

 rushes through the valves in the neck F, and fills the 

 space below the piston. When the piston descends 

 from the top to the bottom of the cylinder, the air 

 below it is condensed, and forced through the valves 

 in the neck H into the pipe L, and thence into the 

 receiver O P, while the space above the piston is a 

 vacuum, and is instantly filled by the rush of the ex- 

 ternal air through the valves in the neck B. This 

 operation is repeated at every stroke of the engine ; 

 the cylinder-full of air, which is inhaled at the necks 

 B and F, being forced through the opposite necks 

 G and H. When the piston reaches the top or bot- 

 tom of the cylinder, there would evidently be a short 

 cessation in the blast of air that passes into the fur- 

 nace, were it not for the regulating receiver O P. 

 When the air is forced into this receiver, the water 

 within it is pushed out or displaced, and rises in the 

 cistern, so that the surface of the water in the cistern 

 is often six, seven, or eight feet higher than the sur- 

 face of the water in the receiver. The air in the re- 

 ceiver, therefore, is pressed upwards by a column of 

 water, six, seven, or eight feet high, so that if there 

 should be any intermission in the supply of air from 

 the cylinder, the blast will be kept up by the extru- 

 sion of the air in the receiver. The receiver O P, as 

 shewn in the Figure, is composed of a great number of 

 cast iron plates, united by screws and (launches. Its 

 size in the drawing is purposely diminished, in order 

 to comprise it within the limits of the Plate. The 

 general size is forty feet in length, twelve feet in 

 depth, and twelve feet in breadth. The water cis- 

 tern is then forty-seven feet long, fourteen feet deep, 

 and nineteen feet broad. The receiver is supported 

 upon blocks of wood and masonry ; its lower edge 

 being two feet from the floor of the cistern, to allow 

 a free passage for the water. The buoyancy of the 

 receiver is overcome by a great quantity of masonry 

 placed upon the top of it ; but we have omitted this 

 in the figure, for the purpose of shewing the manner 

 of uniting the plates of which it is composed. 



A valve, loaded with a weight, is placed at T in 

 the horizontal pipe. The weight is sufficient to keep 

 the valve shut when the engine works with a proper 

 velocity ; but when it works too hard, the excess of 

 air will escape through the valve. When this hap. 

 pens, the velocity of the engine must be diminished. 



The horizontal pipe N M, after bending down- 

 wards, is divided into two branches X, Y, which, by 

 a series of pipes, convey the air round the furnace, 

 so as to introduce the blast at opposite sides of the 

 hearth ; a practice which is now pretty generally 

 followed. 



In the construction of a blowing machine the 

 greatest caution is necessary. The pipes should be 

 carried at such a height above the cistern, that there 

 is no possibility of the water, when at its highest 

 point, being forced through the pipe.s into the fur- 

 nace. 



o 



The cylinder A A is made of cast iron, with a 

 (launch at each end. The upper necks G, B are cat 

 in the same piece with it, but the lower ones, H, F, 

 are screwed to the under (launch of the cylinder. 

 The vaWes within the necks B and F open inwards. 

 They are made of leather, covered with plates of iron, 

 and are screwed, bv a projecting part of the leather, 

 against the external piate a of the chamber, so as to 

 cover three corresponding aperturos in the plate (See 

 Fig. 2.) xy, which is screwed to the neck by a num- 

 ber of bolts, shewn in tfie Figure. This plate is re- 

 moved when the valves require any material repairs ; 

 but any trifling adjustments may be made, by the 

 workman's thrusting his hand through one of the 

 valves to repair the adjacent one. The plates which 

 carry the valves in the chambers I, K, are not move- 

 able ; but apertures are left above to give access to 

 the valves. These apertures, when the engine is at 

 work, are covered by the lids h h, which are fixed 

 down by screws at each end. 



The piston is rendered air tight by means of a ring 

 of leather screwed on the upper and one on the under 

 side of the piston, which, in consequence of their 

 elasticity, press gently against the inside of the cylin- 

 der. In order to renew these rings when worn out, 

 there is a hole in the lid, and another in the bottom 

 of the cylinder, sufficient to admit a man for that 

 purpose. In some cases a moveable lid is made in 

 the piston. 



The cylinder is held down by four large bolts, two 

 of which are seen in the figure at d ^.passing through 

 a massive pier of brickwork or masli^Jfcufficiently 

 stable to keep the cylinder steadily in Ws place. The 

 cistern R S is placed at a much greater distance from 

 the cylinder than is represented in the Figure, lest 

 the tremulous motion produced by the violent concus- 

 sion of the included air should make the cistern leak. 

 An accident of this nature ought to be carefully pre- 

 vented ; as the water which escapes may insinuate it- 

 self into the sand of the casting-house, and occasion 

 the most perilous explosions, when the hot metal is 

 introduced into the moulds. 



The internal diameter of the cylinder A A is five 

 feet two inches, and the stroke seven feet. It is ca- 

 pable of blowing one furnace, when working at the 

 rate of six strokes per minute, (q) 



BLUBBER, the name of the tat which lies un- 

 der the skin of all large fish of the cetaceous kind. 

 See Phil. Trans. N 77. See also Oil and Whale. 



0") 



BLUE colour of the sky. See Atmosphere. 



BOA, a genus of serpents. See Herpetology and 

 Serpent. 



BOADICEA, Boudicia, or Bunduica, a queen 

 of the Iceni, and famous for the formidable resistance 

 which she opposed to the Roman arm9 in Britain. 

 Prasutagus, the king of the Iceni, had submitted 

 with an unworthy humility to the Roman power, 

 and bequeathed his estates to his two daughters and 

 to the Emperor Nero. In carrying this will into exe- 

 cution, Catus Decianus, the procurator, seized upon 

 all the property of the king. Boadicea remonstra- 

 ted against this iniquitous proceeding ; but her bold- 

 ness was punished by the most intolerable outrage? 



Blowing 

 lii.gine 



I 



Boaditea. 



Pl.ATE 

 LX11I. 



Fig. 2. 



