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Niter or saltpeter , ( from which is derived potassium nitrate ) , the main component of black powder , was also mined in Virginia . STSs , which were derived largely from the end clones of cosmid contigs were first localized to a high resolution cytogenetic breakpoint map derived from 78 mouse / human somatic cell hybrids and 4 fragile sites which divide chromosome 16 into 90 intervals of average size 1 Mb . Because this trait is in all members of the ingroup but not the outgroup , we can not tell which form is primitive and which is derived . The principal use for NSCAT was in determining wind-direction , from which is derived useful information relative to ocean waves and global climate patterns .