AND SUHFACE CONDENSER. 345 



tubes are concentric, through the side of which second tube is 

 an opening corresponding with that in the first tube, and the 

 flanch is screwed to the second tube so as to make one opening 

 through the sides of the two tubes. The second tube extends 

 downwards about 5 inches below the first tube, and has a flanch 

 turning inwards, to which a second round plate of iron is 

 screwed, forming the bottom of the boiler. The first tube has 

 an external flanch at the top, and the second tube an internal 

 flanch, both of the same height, and screwed to a cast-iron 

 circular plate or cap-piece, which extends wide enough around 

 the boiler to form also the cover for the air-vessel.. This plate 

 has a hole in the middle as large as the flue. The sides of the 

 con denser and air-vessel are formed of four concentric tubes, 

 each about 2 inches larger than the one within it. The inner 

 and outer of these tubes constitute the sides of the air-vessel, 

 and are each furnished with an external flanch at the top by 

 which they are screwed to the cap-piece. The two intermediate 

 tubes constituting the sides of the condenser are riveted 

 together at the top, leaving a space of about an inch between 

 their upper ends and the cap-piece, so as to allow of a free 

 communication over them between the outer and inner parts of 

 the air-vessel. The inner tube of the air-vessel extends down- 

 wards about an inch below the boiler, and is closed by a flat 

 plate screwed on to a flanch projecting inwards from the tube ; 

 the two tubes of the condenser descend about 3 inches lower 

 th.in the boiler. The inner tube has an internal flanch, to 

 which a flat circular plate is screwed to close up the tube. 

 The outer tube of the condenser is of the same length with the 

 inner, and is provided with an external flanch about 3 inches 

 broad. The outer tube of the air-vessel has an external flanch 

 2 inches broad, and is just long enough to come down upon the 

 broad flanch of the condenser last described, and these two 

 flanches are together bolted upon a bottom piece of cast iron, 

 which is a dish of 4 inches deep, and equal in diameter with 

 the diameter of the outer tube, and having a flanch the same 

 breadth as the flanch of the outer tube, and the bottom piece 

 is secured to the air-vessel and outer tube of the condenser by 

 bolts going through all the three Hanch"s. An opening is 



