"Silica fiber" is the name given to a product being manufactured by the Crystal Chemical Works, of Alexandria, Ind., from a hydrous limestone quarried in that neighborhood. The discoverer of the process is C. C. Hall, a chemist and mechanical engineer of experience in the management of steel works. The name given the product is expressive of its substitution for the purposes for which the commercial product known as mineral wool is adapted, and differs from most articles of that character in being entirely free of sulphur or metallic slag. It is said over 90 per cent, of its composition is the limestone material. This limestone, or cement rock, as it might more clearly be denominated, carries sufficient silica, alumina, lime and magnesia to form a fluid slag, when subjected to a temperature of about 3,500 degrees Fahrenheit. The other ingredients, which are the secrets of the invention, are employed to give the "fluid slag" the desired properties to enable it to be torn into fine shreds by the action of a high-pressure steam jet. No artificial, or refuse material enters into its composition, and no corrosive, destructive or unstable elements are absorbed in its manufacture. Air, moisture or heat are powerless to add to, take away from, or modify its composition; consequently there are no chemical changes to be expected that would form corrosive compounds and break up the fibers of the material, destroying the air spaces and causing shrinkage in volume. Most mineral wools made from furnace slag contain sulphur, and this is added to from the coke used in melting the slag. Sulphur, as is well known, is corrosive of all metallic substances, and its presence in mineral wool, it is claimed by Mr. Hall, tends to disintegrate its fiber and thus impair its value as an insulating material. It was these defects which started Mr. Hall to experimenting for a process in which crude materials absolutely free of sulphur could be employed under conditions and by agencies that would exclude all possibility of introducing it into the fluid matter. After many weeks of experimentation, and the building of several furnaces, it was successfully accomplished. The limestone, of which it is almost entirely composed, is used directly as it comes from the quarry. The process employs the use of two furnaces, one of which is kept at a low temperature and the other at a high temperature. The slag-making qualities of the stone were discovered by Mr. Hall during an analysis he was making to ascertain its value as a flux in steel making.

    The manufacture of silica fiber has been carried on since the first of November last. It is white in color, light for its bulk, a cubic foot weighing when packed about eight pounds. It is soft to the touch, elastic, and warranted indestructible. A patent on it has been applied for.

From: Stone; an Illustrated Magazine, Vol. XVI, Dec 1897 - May 1898, publ. The D.H. Ranck Publishing Co (1898), page 264.  Digitized by Google (source).

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