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

96 SEA WATER DISTILLATION. TABLE L.—Conductivity of various Metals. JRatio. B.T.U Silver, .... . 100 Copper, .... . 74-0 515 Heat passed Gold, .... . 53 0 through a Zinc, .... . 28-1 225 plate 1 in. Brass, .... . 24'0 428 thick, per Tin, . 15 0 sq. ft., per Iron, .... . 120 233 hour. (See Lead, .... 9-0 113 § 57, page Platinum, 8-0 94.) German silver, 6-0 2. Galvanic Action. 59. Secondly, the composition of brass predisposes this metal to galvanic action, when used in a distilling appar- atus. The two metals, copper and zinc, of which brass is composed, are the positive and negative poles of a galvanic battery, thus predisposing the zinc to decom- pose, whilst the gases oxygen and hydrogen are given off at the poles so long as the galvanic action is going on. Brass tubes are always required to be tinned, inside and out, when used either for evaporator or distiller coils, and a very small percentage of tin is specified as part of the admixture. Zinc plates are also ordered to be fixed to the interior of the casing, in order that the galvanic action may act on these zinc plates or blocks, and not on parts of the evaporator. But in spite of it all, brass tubes do perish quicker than copper. 60. The usual way in which such galvanic action shows itself is by the brass tubes becoming pitted by small holes, through which a pin or needle can be readily passed from outside right through the tube, with the result of course, that they cease to be either steam or water-tight, as the case may be. If more tin could be added to the alloy, the above objection might be reduced, but this cannot be done, as to put more than 1 per cent, of tin