In working the plant, the liquor in each vessel is kept at a fairly constant level by judicious feeding from one to the other; the first vessel is, of course, charged with treated lyes. As the liquor acquires a density of 42° Tw. (25° B.) salt begins to deposit, and may be withdrawn into one of the many patented appliances, in which it is freed from glycerine, washed and dried ready for use at the soap pans. Difficulty is sometimes experienced with the tubes becoming choked with salt, thereby diminishing and retarding evaporation. It may be necessary to dissolve the encrusted salt with lyes or water, but with careful working the difficulty can be obviated by washing out with weak lyes after each batch of crude glycerine has been run away, or by increasing the circulation.