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

STEAM. 47 sea water as steam at 10 lbs. pressure will do, and steam at 75 lbs. pressure will (in point of time) evaporate twice as much sea water as steam at 25 lbs. pressure will do. 24. Therefore, with the same amount of coil surface for each case, the 25 lbs. pressure steam will be able to evaporate 2 lbs. of water in the same time that the 10 lbs. pressure steam would take to evaporate 1 lb., and the steam at 75 lbs. pressure will be able to evaporate 4 lbs. of water in the same time as it would take the steam at 25 lbs. pressure to evaporate the 2 lbs. of water. Or, put in another way, it would take the above pressures of 25 lbs. and 75 lbs. half and quarter of the time it takes the steam at 10 lbs. pressure to evaporate 1 lb. of water. This is due to the proportionate intensity of the heat of the steam (at each of the above pressures) above that of the sea water it has to evaporate. 25. In comparing the economy of the above three pres- sures of steam—viz., 10 lbs., 25 lbs., and 75 lbs. pressure— the latent heat required inside the coil has to be kept up so as to be sufficient to meet the latent heat required to evaporate the water owfeide the coil, so that the ratio in each case will be as follows :— As 946 : 966 :: 1 lb. (weight) of steam : 1021 in case (1) As 927 : 966 :: 1 „ „ . : L042 „ (2) As 889 : 966 :: 1 : 1*087 „ (3) which is the same ratio of 1, 2 and 4. Sensible Heat in Primary Water. 26. It must not be forgotten that there is sensible heat still remaining in the primary water produced wiside the coil, after the latent heat has been abstracted, and that this has not yet been counted. When this is taken into