428

MODERN STEAM PRACTICE.

the ring, and the nut being placed over the tube when in Posi-tion, it is screwed up, then the cone is forced through the indiarubber and expands it for the reception of the tube; in this waythe ring is spread out, tightly filling the recess, and binding thetube firmly; the nut is screwed hard up on the tube plate, againsta washer, or simply metal to metal, having a little red lead inter-posed. By this plan the tubes can be readily and quickly madetight, and the elasticity of the ring allows of free movementfor expansion and contraction. Whenindia rubber is used the tube ends shouldbe tinned to prevent the deteriorationwhich takes place when brass and indiarubber are in contact. In some ar-rangements when the water is forcedthrough the tubes, their ends are madetight with a simple flat ring washer ofindia rubber, placed over the tubetightly, the flat end surface bearing onthe tube plate, which is recessed for itsreception, and in others wooden plugsare used, driven over the tubes, andfirmly held in the tube plate, the expan-sion of the wood when wetted makinga very good joint.

The arrangement of the refrigerat-ing surface now falls to be noticed. 1%. 312.—Packing Ring for Tubes.When the water passes through thetubes and the steam all around them,

we obtain a larger amount of surface than when the steam isCondensed inside of the tubes; but in the former case any incrus-tation that takes place tends to choke up the spaces betweenthe tubes, and so far renders them useless, as there is no pos-sibility of getting them cleaned; whereas, when the steam is Con-densed inside of the tube, the surface can be cleansed occasionally.Again, should any of the tubes require repacking at sea, with thewater circulating around them, the large covers which form part ofthe condenser require to be taken off, and should any leakageoccur through the joint being imperfectly re-made, air finds its wayinto the chamber and impairs the vacuum; whereas, when thewater passes through the tubes, with any leakage occurring, the