398 2^^^ Philippine Journal of Science 



about 5 centavos, and the annual yield is about 100 kilograms of 

 salt. By the use of covers the average annual yield could be 

 increased to 118.7 kilograms and in exceptional seasons to 153 

 kilograms with very little additional labor. The original cost 

 of arranging movable roofs in such a way that they can be slid 

 easily over the vats when it rains would not exceed 50 centavos 

 per square meter, and the life of the roofs would be at least 

 five years. The increased output of an average season would 

 return 50 per cent of the additional outlay, and in exceptionally 

 favorable seasons this would be increased three-fold. Further- 

 more the season could be considerably prolonged, thereby still 

 further increasing the yield. No strong brine would ever be lost 

 at the end of the season, as the evaporation could be finished 

 entirely under cover, if necessary. 



The fact must be recognized that the producers, in general, are 

 not obtaining the best practical results. Many of them are un- 

 willing to change their methods, while others cannot without 

 previous study, for which they have neither time nor opportu- 

 nity. The foundation for such a study is the collection of man- 

 ufacturing statistics from the native works and their careful 

 comparison with each other and with the best results of foreign 

 practice. The results of our study thus far lead to the following 

 conclusions. 



CONCLUSIONS 



The brine should not be transferred to the crystallizing ponds 

 until the salt is ready to crystallize out (specific gravity, 1.205; 

 25 °C.), for in the evaporation reservoirs large quantities of gyp- 

 sum and other matter had precipitated before the salt settled out. 

 If there is a proper balance in the plant, in at least the last two 

 reservoirs large quantities of undesirable substances will be re- 

 moved and a purer grade of salt will result. 



The area occupied by the crystallizing ponds should be as small 

 as possible to accommodate the brine concentrated in the evapo- 

 ration reservoirs, for in that way as much salt is obtained with 

 less labor. When the strength of the brine in the crystallizing 

 ponds has attained 1.275 specific gravity (29°C.), it should be 

 drawn off and worked over for the by-products or should be dis- 

 carded. Experiments show that salt with a purity of 99.63 

 per cent sodium chloride may be obtained with these precau- 

 tions.^* Effort should be made to improve the quality of the 

 output and to develop a larger industry in the Philippines. 



'*18th Annual Rept. U. S. Geol. Surv. (1897), 5, 1311. 



