Lute, Or Luting, (Lat. Lutum clay), a soft adhesive mixture used in chemical operations for making tight the joints of an apparatus. Its ingredients vary according to the kinds of vapors to be confined, and the temperatures to which it is to be exposed. Fire-brick clay, finely pulverized and made into a paste with water, withstands the highest degrees of heat, and makes tight joints when carefully applied and gradually dried and baked. Fibres of as-bestus are advantageously intermixed with the clay. Fat lute is very generally used where the temperature is not excessively high, and where the vapors to be confined are corrosive. It is made of pipe clay worked to a soft and ductile paste with linseed oil. It must be applied to perfectly dry surfaces, and may be strengthened by binding over it slips of bladder. Common putty may often be substituted for it. Hydraulic lime and plaster of Paris make very useful lutes for many purposes, especially when rendered impervious by washing them over with oil, or a melted mixture of equal parts of wax and oil. Caustic lime thoroughly worked into the white of an egg, laid on slips of cloth and thus applied over the junctions to be luted, firmly adheres like a cement.

White lead and oil laid on slips of cloth, and paste and paper, or glue and paper, and linseed meal made into a paste with water, milk, lime water, or weak glue, all serve as lutes for special operations.