Part 18

4. Pitch 8 parts Rosin 6 parts Wax 1 part Plaster 1⁠/⁠4 to 1⁠/⁠2 part

5. Pitch 8 parts Rosin 7 parts Sulphur 2 parts Stone powder 1 part

These compositions are used to unite slate slabs and stoneware for domestic, engineering, and chemical purposes. Various rosin and pitch mixtures are used for these purposes, and the proportions of these two ingredients are determined by the consistency desired. Sulphur and stone powder are added to prevent the formation of cracks, sulphur acting chemically and stone powder mechanically. {34} Where the lute would come in contact with acid or vapors of the same, limestone should not be the powder used, otherwise it is about the best. Wax is a useful ingredient to keep the composition from getting brittle with age.

A class of lutes under this general grouping that are much used are so-called “marine glues” (q. v.). They must be tough and elastic. When used for calking on a vessel they must expand and contract with the temperature and not crack or come loose.

Formulas:

6. Pitch 3 parts Shellac 2 parts Pure crude rubber 1 part

7. Pitch 1 part Shellac 1 part Rubber substitute 1 part

These are used by melting over a burner.

VI. Rosin, Shellac, and Wax.—A strong cement, used as a stone cement, is:

1. Rosin 8 parts Wax 1 part Turpentine 1 part

It has little or no body, and is used in thin layers.

For nitric and hydrochloric acid vapors:

2. Rosin 1 part Sulphur 1 part Fire clay 2 parts

Sulphur gives great hardness and permanency to rosin lutes, but this composition is somewhat brittle.

Good waterproof lutes of this class are:

3. Rosin 1 part Wax 1 part Powdered stone 2 parts

4. Shellac 5 parts Wax 1 part Turpentine 1 part Chalk, etc. 8 to 10 parts

For a soft air-tight paste for ground-glass surfaces:

5. Wax 1 part Vaseline 1 part

6. A strong cement, without body, for metals (other than copper or alloys of same), porcelain, and glass is made by letting 1 part of finely powdered shellac stand with 10 parts of ammonia water until solution is effected.

VII. Rubber.—Because of its toughness, elasticity, and resistance to alterative influences, rubber is a very useful constituent in lutes, but its price makes its use very limited.

Leather Cement.

1. Asphalt 1 part Rosin 1 part Gutta percha 4 parts Carbon disulphide 20 parts

To stand acid vapors:

2. Rubber 1 part Linseed oil 3 parts Fire clay 3 parts

3. Plain Rubber Cement.—Cut the crude rubber in small pieces and then add the solvent. Carbon disulphide is the best, benzol good and much cheaper, but gasoline is probably most extensively used because of its cheapness.

4. To make corks and wood impervious to steam and water, soak them in a rubber solution as above; if it is desired to protect them from oil vapors, use glue composition. (See Section IX.)

VIII. Linseed Oil.—This is one of the most generally useful substances we have for luting purposes, if absorbed by a porous substance that is inert.