X. A, 6 Cox and Da?' Juan: Salt Industry and Resources 397 



of six months it rained on thirty-two days ; on eighteen of these 

 days more water fell into the ponds than was evaporated from 

 them. Even in the most favorable four months of this season 

 more than one fifth of the water evaporated from the ponds was 

 returned by rain and therefore the effective evaporation was only 

 four fifths of the apparent. If the ponds had been covered 

 during the whole period, four fifths as much water would 

 have been evaporated as was evaporated in free exposure; in 

 other words, if the ponds had been covered during the whole 

 season, the evaporation would have been at the rate of the ef- 

 fective evaporation during the most favorable month, but with 

 the proper system it would have been unnecessary to cover them 

 except on the days when there was precipitation. 



Solar salt is manufactured at Syracuse, New York, and other 

 places by evaporating brine on so-called covers — shallow wooden 

 vats provided with light, movable roofs arranged in such a way 

 that they can be easily shoved over the vats when it rains. The 

 improved process consists in the use of "aprons," or very wide, 

 shallow troughs, in complete exposure to the sun, air, and wind, 

 which convey the brine from the wells to the salt fields; these 

 are 5 to 6 meters wide by 6 or 7 centimeters deep. Upon this 

 the brine, kept at a depth of from 1 to 2 centimeters, flows slowly, 

 depositing the gypsum and being delivered in a saturated con- 

 dition to the covers. The grade is usually from 1 centimeter to 

 10 meters. Under the aprons are deep rooms or tanks so placed 

 that, in case of rain, the brine on the apron can be discharged 

 into the deep room, where it is protected from dilution, remain- 

 ing there until the return of fair weather, when it is pumped 

 back into the apron, from which all rain water has been drained. 

 With this improvement the efficiency of a cover has been in- 

 creased over 80 per cent in many instances."^ Natural brines, 

 which are sometimes very dilute, are often concentrated by drip- 

 ping over extensive ricks composed of twigs. In the Philippines, 

 where nipa and grass roofs are so cheap and comparatively 

 durable, we believe a great deal might be done in the adaptation 

 and utilization of these ideas. 



The following illustration will serve to show the saving to be 

 effected by the use of covered vats. A crystallizing pond one 

 meter square originally costs about 1 peso ; the annual upkeep is 



-^Annual Rept. Supt. Onondaga Salt Springs, N. Y. (1851), 27; ibid. 

 (1869) ; Goessmann, C. A., Rept. on the manufacture of solar salt, Syracuse 

 (1864); Carrignes, S. S., Statistics relating to the silica interests of 

 Michigan, Lansing (1881), 23; Chatard, T. M., 7th Annual Rept. U. S. 

 Geol. Surv. (1886), 506. 



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