The United States, the largest consumer of mica among the nations of the world, has relied upon imports to supply a considerable part of the consumption and will probably continue to do so in the future, although steady development of domestic sources of supply may be expected. Brazil offers the most promising foreign field for the development of an independent source of supply for American markets.
CHAPTER XXIV
ASBESTOS
By Oliver Bowles
USES OF ASBESTOS
Asbestos is useful because of its incombustibility, insulating qualities, and fibrous structure. High-grade asbestos is spun or woven into ropes and fabrics, the fabrics being used for many purposes, such as safety curtains, mats, mattresses, upholstering, firemen’s suits and gloves. Of late years much high-grade asbestos has been used for friction facings in brakes and for packings. Low-grade asbestos is used for a great many purposes, which may be classed in three groups—building, insulating, and miscellaneous.
For building purposes asbestos is employed in many ways. A mixture of asbestos and cement is used to make fireproof shingles or slates. Asbestos is also used with Portland cement to make a protective surface on metal sheathing; asbestos paper is used for weather and sound proofing and also for fire-protection purposes. It is used widely for plaster, which not only is fireproof but also improves the acoustic properties of auditoriums, churches, etc. Asbestos is also used for floor tiling and in the manufacture of paints. Asbestos lumber and millboard are employed for many structural purposes.
Asbestos cement, a mixture of asbestos fiber and clay, is much used as a covering for boilers and steam pipes to prevent heat radiation. Other coverings are made from a mixture of asbestos and magnesia. Varieties of asbestos having a low iron content are useful for electrical insulating purposes.
Some of the many miscellaneous uses of asbestos are for fire brick, acid filters, lead-fume collectors, stove mats, cooking-utensil linings, etc.
The most essential of the above uses are those in which the long-fiber asbestos is employed. For fireproof ropes and fabrics nothing can take its place. Its use in friction facings for brakes is essential in all motor vehicles.
The uses for which low-grade asbestos is employed may be regarded as less essential and might be eliminated in case of necessity, though such elimination would no doubt involve many serious difficulties. Fire risk would thereby be increased and many boilers and heating plants would be rendered less efficient and more wasteful, though these difficulties could be overcome to some degree by the use of substitutes.