Chemical substance identity of benzene, until the correct structure was described by Friedrich August Kekulé. Likewise, the idea of stereoisomerism – that atoms have rigid three-dimensional structure and can thus form isomers that differ only in their three-dimensional arrangement – was another crucial step in understanding the concept of distinct chemical substances. For example, tartaric acid has three distinct isomers, a pair of diastereomers with one diastereomer forming two enantiomers. An element is a chemical substance made up of a particular kind of atom and hence cannot be broken down or transformed by a chemical reaction into a different element, though it
CSX milepost prefixes Also, like the ACL, the SAL mainline ran from Richmond, Virginia to Tampa, Florida. The S Line is today discontinuous and segments of the original line have been abandoned (notable abandoned segments are between Chester, Virginia and Norlina, North Carolina, and between Riceboro and Seals, Georgia. The Seaboard main line from Richmond to Tampa, heart of its 2600-mile system in 1900, had been built by the following companies: CSX milepost prefixes Most CSX railroad lines are given lettered prefixes before milepost numbers. These prefixes are one to three letters long with the first letter usually refer to the former company.