Abstract: The invention involves visbreaking heavy oil under mild conditions in a vertical vessel containing a vertical elongate ring spaced inwardly from the vessel wall to form an outer open-ended annular chamber and an inner open-ended soak chamber. Heavy oil at 220.degree.-600.degree. F. is fed to top of annular chamber. A mixture of visbroken residuum and heavy oil at 730.degree.-800.degree. F. is fed to top of soak chamber. There is heat transfer through the ring from the soak liquid to the annulus liquid to assist in maintaining mild temperature in the soak chamber. The two streams mix in the base of the vessel whereby the visbreaking reaction is quenched. Part of the product is recycled and heated to provide the feed to the soak chamber.

Abstract: An improved stationary nut for a harp, for adjusting the position of a harp string relative to sharpening pins of an action plate, includes: an annular collar defining a central bore and, on its outer surface, a generally circumferential groove sized and adapted to be engaged by the harp string, and an elongated shaft sized and adapted to extend through the central bore for fastening the annular collar to the harp. The relative axes of the elongated shaft and the generally circumferential groove defined about the collar are different, and relative rotation between the collar and the shaft is effective to change the radial distance of a segment of the groove surface supporting the harp string from the axis of the shaft in a manner to change the position of the string relative to the sharpening pins, whereby the harp string may be centered on the action plate, between the sharpening pins, for improved playing tone. A harp employing the improved stationary nut is also described.