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

THE EVAPORATOR. 127 134. This matter of a sufficient delivery area can be illustrated by comparing the boiling of ordinary water in a narrow test tube and in an open beaker. Fill a test tube about half full of water, and hold it over a Bunsen gas flame. When the water boils the ebullition will be very violent, and probably be sufficient to shoot the water out of the test tube. Next, fill a small beaker about half full of water, hold it over the same flame, and it will boil quietly, without anything like the agitation that was seen when using the test tube. This difference is due to the small area on the top of the water in the test tube, as compared with that in the beaker. In the test tube there was not sufficient area for the steam that was being generated to deliver itself freely, and the consequence was that the water was shot out by the steam being unable to get through to the surface. As the beaker had sufficient area for its steam to escape, the delivery was quiet, without any sudden discharge of boiling water. 135. Applying this to the area of the brine in an evap- orator, it shows that it is a most important point to have a sufficient surface area for the gentle delivery of the steam. 136. To a small extent this delivery area is affected by the pressure over the brine, because when under high pressure the same weight of steam has a smaller volume, and, therefore, a smaller area should be sufficient for the amount of water that is being evaporated ; below atmo- spheric pressure, the same weight of steam would have a larger volume. The question of more or less pressure has, however, less effect on the sufficiency of brine area than one would expect. 137. The exact amount of brine area for a given output of steam is difficult to determine, as so many considera-