A Practical Manual On Sea Water Distillation
With A Description Of The Necessary Machinery For The Process

146 SEA WATER DISTILLATION. Similar sheaves of copper tubes show no such inclination to perish. Note.—It is thought advantageous to have brass tube plates and brass tubes, so as to have all of same metal; but copper tubes with gun-metal plates would seem to offer practically the same advantages. (2 ) With regard to the conductivity of the two metals, what has already been said when dealing with the heating surfaces of the evaporator need not be repeated here, to show that a copper sheaf is about 20 per cent, more effective than a similar sheaf made of brass tubes (see p. 96). 24. The form of the surfaces varies with distiller makers. The most usual form is that of a set of tubes (copper or brass, as the case may be) either straight or coiled, but still of ordinary pipe shape. This is the most usual, but some makers prefer tubes that are flattened either at specified distances, or in such a manner as they think most scientific. 25. The size of tubes usually put in distilling con- densers is f or I inch in outer diameter, and the thickness 18 I.S.W.G. The tubes (tinned throughout) are best expanded in the plates. The test pressure is usually 30, 40, or 50 lbs. per square inch. 26. The space between the tubes varies from about (4 inch, in small size tubes, to 1| inch, in tubes of larger diameter. The object, of course, is to put the tubes as close together as possible, in order to get the maximum of surface in the minimum of space, consistent with the water circulating freely, and the easy removal of the scale formed outside the tubes.