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

MULTIPLE DISTILLATION. 223 —viz., the boiler pressure, the water level in boiler and in each evaporator, and the speed of the pump should all be as at starting—otherwise the trial will not be of much value. This applies most to the boiler pressure being the same (certainly not lower) when the trial ends, for if the boiler pressure is less at finish than at start, an obvious advantage is given to the apparatus, which it cannot maintain in general working. In a short trial, the temporary advantage cannot be spread over a sufficient length of time to minimise it. Note.—The advantage gained by thus working the boiler is the uncounted supply (before commencing the trial) of the amount of coal used for getting up steam, from the low pressure recorded at finish to the higher pressure at which the trial commenced. This spread over a short trial would be of con- siderable value, and the shorter the trial, the more pronounced would be the saving ; therefore, an economy based on such a record would be somewhat misleading, as a quantity of coal is used to advantage without being counted. (4) As it is very easy to get into a state of confusion as to the quantity of coal actually consumed, a good way of recording the same is to have several lots of coal (if coal is the fuel used) weighed out in separate lots of, say, 100 or 200 lbs. each, and to keep a double record (1) of the quantity taken from each lot, and (2) the quantity when the last shovelful of coal is put into the boiler furnace. (5) At the conclusion of the trial the total weight of water delivered should be taken as against the weight of the coal consumed, and the latter should include the