The purification of seal oil

The oil, in its raw state, is filtered through bags about 41 inches long, with circular mouths extended by a wooden hoop about 15 inches in diameter, fixed thereto. These bags are made of jean lined with flannel, between which jean and powdered charcoal is placed, throughout, to a regular thickness of about 1/2 inch, for the purpose of retaining the glutinous particles of the oil and straining it from impurities; and the bags are quilted, to prevent the charcoal from becoming thicker in one part than another, and to keep the linings more compact. The oil is pumped into a large funnel made of tin, annexed to the pump through a perpendicular pipe, and passed from the funnel into another pipe placed over the bags horizontally, from whence it is introduced into them by cocks. The oil runs from the filtering bags into a cistern about 8 feet long by 4 feet broad, and 4 1/2 deep, made of wood and lined with lead and containing water at the bottom about the depth of 5 or 6 inches, in which are dissolved about 6 oz. of blue vitriol, for the purpose of drawing down the glutinous and offensive particles of the oil which have escaped through the charcoal; and thereby rendering it clean and free from the unpleasant smell attendant upon the oil in the raw state; and in order to enable the oil thus to run from the bags, they are hung in a frame or rack made like a ladder, with the spokes or rails at sufficient distances to receive the hoop of the bag between two; and such frame or rack is placed in a horizontal position over the cistern. The oil is suffered to run into the cistern until it stands to the depth of about 2 feet in the water, and there to remain for 3 or 4 days, (according to the quality of the oil), and is then drawn off by a cock which is fixed in the cistern a little above the water, into a tub or other vessel, when it will be found to be considerably purified and refined; and the oil after having undergone this operation, may be rendered still more pure by passing a second or third time through similar bags and cisterns. But the oil after such second and third process, is drawn off into and filtered through additional bags made of jean lined with flannel, inclosed in other bags made of jean, doubled, when the process is complete.

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