Colza, carcel or rape-seed oil gave a clear, smokeles, odourles flame, but was too heavy to move easily to the lamp's wick. Lamps therefore employed various devices to enable the oil to reach the wick. The early example on the right contains a two-cylinder clockwork driven pump to force heavy colza oil up to an argand wick. Exces oil found its way back to the main reservoir. The 'Moderator' lamp, shown here on the left, was patented by Franchot in 1836 and forced the oil up the wick by spring presure.
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