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Rh salt stacks and six of the windmills, together with many smaller piles of salt. Fig. 197 is a closer view of the evaporation basins with piles of salt scraped from the surface after the mother liquor had been drained away. The windmills, which were working one, sometimes two, of the large wooden chain pumps, were some thirty feet in diameter and lifted the brine from tide-water basins into those of a second and third higher level where the second and final concentration occurred. These windmills, crude as they appear in Fig. 198, are nevertheless efficient, cheaply constructed and easily controlled. The eight sails, each six by ten feet, were so hung as to take the wind through the entire revolution, tilting automatically to receive the wind on the opposite face the moment the edge passed the critical point. Some 480 feet of sail surface were thus spread to the wind, working on a radius of fifteen feet. The horizontal drive wheel had a diameter of ten feet, carried eighty-eight wooden cogs which engaged a pinion with fifteen leaves, and there were nine arms on the reel at the other end of the shaft which drove the chain. The boards or buckets of the chain pump were six by twelve inches, placed nine inches apart, and with a fair breeze the pump ran full.

Fig. 196.—Salt stacks and salt windmills on the Taku evaporation fields at the mouth of the Pei ho, Chihli.