The Fractionation still is outside the north-west corner of the Chemist's house in western Rimmington. It is "a still for fractionating oils".
Fractionation still location

The location of fractionation still

It is required in the Regicide and Mourning's End Part I quests to change a Barrel of coal-tar to a Barrel of naphtha.

How to use Fractionation still

First, use the barrel of coal-tar with the Fractionation still.

Fractionation still operate

Operating the fractionation still

Then, click the right side of the valve to the right twice; the tar should be flowing at maximum. One should see the 'pressure' indicator on the left rise. When the indicator reaches the green region, click the right side of the valve on the left once to let out pressure. This should stall the indicator on the left. Now you can start adding coal (you need 6-8 per barrel). This will raise the indicator on the right. If the heat gauge is below the green region, add more coal. If it's above, don't add coal until it gets lower. The bar on the bottom will start turning green, when it's full you can stop adding coal and close the window on the top right to get your barrel of naphtha.

Making naphtha

Making Naptha

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