Traditionally, canal locks were made waterproof by the use of a hydraulic  cement
               composed in part of  volcanic ash.  This ash, known as trass, was effective but
               expensive because the ash was imported from the Rhine river or from Pozzuoli, Italy.
               When the canal committee found that a similar ash was available from the Dutch
               West Indies it commissioned Josiah Banks, captain of the sloop Industry, to return
               with a cargo of forty tons of trass, or Dutch Terras as it was called.

               The accepted procedure in forming the hydraulic cement had been to mix the trass
               with lime and water and then to beat it for a long time - the longer the mixture was
               beaten the harder the cement set. Loammi Baldwin found that by pulverizing the
               trass to a very fine powder before mixing, the time-consuming beating process was
               overcome and the mortar set just as hard as with the old system.
     
     
     	
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