Lutes always consist of a menstruum and dissolved or suspended solids, and they must not be attacked by the gases and liquids coming in contact with them. In some cases the constituents of the lute react to form a more strongly adhering mass.

The conditions of application are, in brief:

(a) Heating the composition to make it plastic until firmly fixed in place.

(b) Heating the surfaces.

(c)   Applying the lute with water or a volatile solvent, which is allowed to volatilize.

(d)   Moistening the surfaces with water, oil, etc. (the menstruum of the lute itself).

(e)   Applying the lute in workable condition and the setting taking place by chemical reactions.

(f) Setting by hydration.

(g) Setting by oxidation.

These principles will be found to cover nearly all cases.

Joints should not be ill - fitting, depending upon the lute to do what the pipes or other parts of the apparatus should do. In most cases one part of the fitting should overlap the other, so as to make a small amount of the lute effective and to keep the parts of the apparatus rigid, as a luted joint is not supposed to be a particularly strong one, but rather one quickly applied, effective while in place and easily removed.

Very moderate amounts of the lute should be used, as large amounts are likely to develop cracks, be rubbed off, etc.

A classification may be given as follows:

(1)

Plaster of Paris.

 

(2)

Hydraulic cement.

 

(3)

Clay.

 

(4)

Lime.

 

(5) Asphalt and pitch.

 

(6)

Rosin.

 

(7)

Rubber.

 

(8)

Linseed oil.

 

(9)

Casein and albumen.

 

(10)

Silicates of soda and

oxychlo-

ride cements.

 

(11)   Flour and starch.

(12)   Miscellaneous, including core compounds.