If one purifies spirit through activated carbon in a pipe and pass the same spirit twice or more through the same pipe the result will be a deterioration.
This is because the pipe method, apart from giving excellent absorption of impurities, has a further function. The impurities are loosely bound to the carbon granules (activated carbon has an affinity charge) most being bound at the top of the pipe and the least at the base. This is one of the reasons why the pipe method (percolation through a thick active carbon layer) is superior to all other activated carbon filtering methods.
So if the same spirit is passed through a second time the loosely bound impurities are pulled down a bit further and some come out with the spirit. Double filtration using the same activated carbon gives inferior results.
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