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

I 20 SEA WATER DISTILLATION. can enter at the bottom part of the heater casing, rise up in between the tubes, and escape at the upper part of the shell into the evaporator. The feed-water can run or be pumped through the heater as may be arranged. The primary water should be blown into the heater tubes, preferably at the top end, so as to force itself downwards, imparting its heat to the feed-water as the primary water passes to the lower outlet of the sheaf, which should be connected to the pipe leading it to the feed-tank, or where else desired. Economy on Steam Ships. 115. On steam ships the only way in which the economy of a distilling apparatus can be counted is by measuring the weight of primary water against the weight of the secondary water produced. By doing this the coal con- sumption is indirectly got at, because we know that the heat absorbed to convert every lb. of water into 1 lb. of primary steam is the same (waste excepted) as the heat that the 1 lb. of primary steam will impart on its being re-con- verted into primary water. Therefore, if 1 lb. of coal will yield 10 lbs. weight of primary steam, and it takes 1'2 ]bs. of primary steam to evaporate 1 lb. of gained steam, the 1 lb. of coal will yield the following proportion of gained steam :—As 1’2 : 1 :: 10 : 8'33—i.e., 8*33 lbs. of gained steam per 1 lb. of coal. In “ multiple ” distil- lation this ratio of water to coal will be dealt with more exhaustively. 116. It should also be noted that the economy of using “ exhaust ” steam instead of “ live ” boiler steam is further enhanced by the fact that the exhaust steam has done its work—i.e., it has no further useful purpose, but simply goes into, and out of the surface condenser as so