The process of manufacture consists in mixing about 25 per cent. of asbestos fibre with about 25 or 35 per cent. of powdered sulphate of alumina. This mixture is moistened with an aqueous solution of chloride of zinc. The mixture is washed with water and then treated with an aqueous solution of ammoniacal gas. The mixture is again washed and then treated with a solution composed of one part of resin soap and eight or ten parts of water mixed with an equal bulk of sulphate of alumina, which should be us pure as possible. The mixture thus obtained should have a slightly pulpy consistency. Finally, there is added to it 35 per cent. of powdered asbestos and 5 to 8 per cent. of white barytes. This pulp is treated with water in an ordinary paper machine, and worked just like paper pulp.
In order to manufacture a solid cardboard from asbestos which shall be proof against fire and water and capable of serving as a roofing material, sheets of common cardboard, tarred or otherwise prepared, are covered with the pulp. The application is made in a paper machine, the pulp being allowed to flow over the cardboard. Among other uses, the asbestos paper has been recommended for the manufacture of cigarettes, though its applicability for this purpose is not so readily seen.
Manufactured into paint, the demand for it is continually increasing. It is used in the Houses of Parliament, as it was in very large quantities at the several recent exhibitions at South Kensington.
In the form of cement there is nothing equal to it as an efficient covering for boilers, steam pipes, hotblast furnaces, stills, &c. For this purpose it is made of about the consistency of mortar and spread on with a trowel in the ordinary way. Certain chemical ingredients have to be added, which, while not injurious to the metal, cause the asbestos to adhere firmly to the plates, so that when dry it becomes quite hard and can be walked over without being injured. With a boiler carrying say 80 lbs. steam pressure, the application of from 1-½ to 2 inches of this composition so well retains the heat in the boiler, that a thermometer with the bulb held close to the outer surface of the covering will not indicate more than 80° to 85° Fahrenheit. Boilers, steam pipes, &c., covered in with this composition will, it is asserted by the manufacturers, effect a saving of as much as 33 per cent. in fuel.[10]