Glycerin from Candle-Works Sweet Water: Cap's Process

The sweet water washed out of lime soap in the stearin candle works holds the fat's glycerin, with lime and fatty traces. Cap's process, given in Muspratt's Chemistry (1860), turns it into glycerin: the lime is thrown down as sulfate with sulfuric acid, the liquor is boiled down out of contact with the air, neutralised with chalk, filtered, cleared with bone black and concentrated to a colourless syrup of about 51° Twaddell.