388 ^^6 Philippine Journal of Science 1916 



are the only ones which exist. With proper manipulation the 

 Bait produced by the Chinese method will have as high a per- 

 centage of purity and a whiter color than that produced by 

 the Filipino method. 



So far as we have been able to determine, the area devoted 

 to crystallizing ponds in plants using the process introduced by 

 the Chinese is one sixth to one fifth (excluding the fish pond), 

 or even more, of the area covered by the evaporation reservoir. 

 However, taking into consideration the fact that for the more 

 complete separation of the less soluble salts the volume of the 

 brine should be reduced more than is done in common practice, 

 the above ratio is much larger than is necessary. 



In order to carry on the process of evaporation in the most 

 efficient way, the following facts should be given due consid- 

 eration : 



1. The rate of evaporation for any solution decreases as the con- 

 centration is increased. Accordingly, in order to counteract retarded 

 evaporation in the various steps of the process a slightly greater than 

 proportional surface area is needed in succeeding concentration reservoirs. 

 This fact is almost negligible except in fairly concentrated solutions 

 and is probably more than compensated by seepage. The latter varies, 

 depending on the nature of the soil, and the average should be determined 

 and taken into consideration in the construction of a plant. 



2. The capacity and surface area of the evaporation resei'voirs of any 

 Tovr should be proportional to the quantity of brine delivered from the 

 reservoirs of the preceding row. 



3. The specific gi-avity of the brine should be controlled in such a way 

 that each row of evaporation reservoirs should receive and deliver a brine 

 of definite specific gravity. 



4. The area occupied by the crystallization vats should be as small 

 as possible to accommodate the brine concentrated in the evaporation reser- 

 voirs, for in that way as much salt can be obtained with less labor. 



If we neglect the effect of the precipitation of the less soluble 

 salts (calcium sulphate, calcium and magnesium carbonates, 

 oxides of iron and alumina, etc.) on the density of the brine 

 during the process of concentration, we can establish for prac- 

 tical purposes the principle that the density of the brine varies 

 inversely proportional to its volume and for a given depth in- 

 versely proportional to the superficial area." 



The salt supply of Mountain Province for the greater part 

 comes from Cervantes and is sold to the people at exorbibant 

 prices. The people of Mountain Province also produce a very 



" On this basis the approximate volume of the brine at any given den- 

 sity may be determined and the corresponding size of the concentration 

 reservoir to contain it may be calculated. 



