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

THE EVAPORATOR. 129 ating surfaces have assumed various shapes and forms, the brine level has to be adjusted by experience, so that the greatest effect can be obtained without causing priming to set in. 140. In this respect, coils, when they are laid hori- zontally, do not act in quite the same way as a vertical sheaf of tubes. Thus, in the vertical sheaf, the only method of stopping a tendency to prime is to lower the level of the brine until the priming ceases. To such an extent does the brine have to be lowered that, when dealing with some sea waters, the level has to be reduced to less than half its usual height before any primary steam can be turned into the sheaf. A set of horizontal coils, however, shows that if they are entirely immersed in the brine, a tendency to priming is created, that this tendency decreases as the level of the brine is lowered, and that when the level gets too low priming begins again. 141. Numerous experiments have been made to ascer- tain what is the best level to work at, with the present form of separate coils (usually lying more or less hori- zontally in the brine). Apparently it is that at which the top coil only is not immersed, which would indicate that the top coil has the effect both of dealing with the frothy matter at the top of the brine surface, and possibly acting also as a baffle. All the coils appear, however, to do their work equally, if one may judge from the amount of scale deposited on the coils when they are taken out to be cleaned. 142. As it is important to keep the brine level steady, an automatic discharge, which compels the brine to escape at a constant level, is a great advantage; for no amount of care and watching can possibly ensure so steady a level.