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 quant.i.ties 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- 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 a.s.serted by the manufacturers, effect a saving of as much as 33 per cent. in fuel.[10]
This cement, which is made from a very cheap quality of asbestos, is now in common use in Canada and the States, where, as already shown, it is found to operate with a twofold effect, viz. by lowering the temperature of the boilerhouse, to the great comfort of the engineers and firemen, and also, in a very marked degree, economising the expenditure for fuel.
It seems, therefore, strange that its use in this country has as yet made so little headway. In one of the large palatial buildings recently erected in London, where engines are required to be in constant work for pumping water for working the lifts and for general purposes, as well as for the dynamos, the heat from the boilers forms so great a nuisance, and occasions so much loss in other ways, that very considerable expense is about to be incurred, with a view to lowering the temperature. When conversing recently with an expert on this subject I asked whether the use of asbestos would not effect the desired object. Yes, he answered, it would, but it is too expensive. This certainly seems very strange, as I know that the cement composition referred to is made of the very commonest quality of asbestos, of the refuse, in point of fact, which could probably be used for no other purpose. The expense, therefore, cannot be great, and as to its mode of use, it is simply laid on with a trowel, like mortar or any similar composition, and when once done is singularly effective. I have stood in an engine-house where the boilers were covered with about two inches in thickness of this cement, which then showed a hard, dry, firm surface; and, when the engines were in full work, on placing one"s hand on the covering there was little more than a gentle warmth perceptible on the outside surface of the composition, whilst the surrounding atmosphere was scarcely, if at all, affected by the heat from the boilers. The boiler quiltings referred to on a previous page as being manufactured by a New York firm under contract with the United States Government, for use in some of their model war ships, would no doubt be as effectual for the purpose, but naturally they would be more costly, being an altogether different contrivance, and made so as to be easily removable when required, which, of course, is not the case with the so-called cement. There is little doubt, however, that, although the use of asbestos in this form does not seem to find much favour here, its use for the purpose of coating boilers and steam-pipes will presently become as general in England as it already is on the other side, where its valuable qualities seem to be so much better known and appreciated.
Improved stove pipings are now being manufactured in the States which in appearance exactly resemble cast-iron. These have the additional valuable properties of extreme lightness, combined with great strength and a capability of ornamentation un.o.btainable with the usual cast-iron pipes mostly in use; paint in the case of the asbestos pipes not scaling off under heat as it will do in the case of ordinary iron pipes. The manufacturers of these pipes claim for them that they combine the strength of steel with the lightness of paper. Tubes also are made for electrical engineers which provide them with a non-conducting covering for their wires both fire and waterproof, so as to preserve the perfect insulation of the wire.
Asbestos rope is used for fire escapes and similar purposes, as well as for the transmission of power over places exposed to heat. In dyeing and printing cloth it is frequently necessary to hang the fabric in loops from parallel rods for exposure to steam, air or ammonia. In order that it should hold upon the rods, without straining or slipping, rope or strips of cloth are usually wound around the poles, but this does not remove, although it mitigates, the difficulty, because the heat and corrosive action of the vapours will rot any covering; the first notice of the deterioration being generally the appearance of small pieces of rod covering among the cloth which is in process of finishing. Asbestos rope and cloth are now largely manufactured and used for this purpose in the United States with very beneficial results.
In commenting on the recent loss of life occasioned by the panic at the fire at the Exeter Theatre, a well-known journal, speaking of the various modes of providing for escape, mentions the case of a man of fashion, a millionaire, who died not long ago, and says that he would never go to bed in a strange house without having an apparatus of knotted rope affixed to a ring in the wall, by which he might lower himself to the ground on an emergency. But, asks the journalist, what if the rope itself took fire? The answer naturally is, let it be an asbestos rope, then it will neither burn nor rot.
The use of the fibre in the manufacture of gas stoves is too well known to need any remark.
As a lubricant it is unrivalled.
Another very important use to which it is now being applied is in the manufacture of filters. These are specially useful where the liquid to be filtered is of a caustic or strongly acid nature, or where the filter with residue is to be ignited without consuming the filter, or where the residue is to be subsequently dissolved off the filter by acids or other solvents. In many cases a very finely divided asbestos is desirable.
This is accomplished by a process recently patented in Germany by Fr.
Breyer, of Vienna. The asbestos is first coa.r.s.ely ground, and then mixed with some granular crystalline carbonate, which must be soluble in acids. The carbonate should possess a hardness between 3 and 4, 5, according to the mineralogical scale. The mixture is ultimately ground together in a mill. Afterwards the ma.s.s is treated with an acid until the carbonate has been dissolved out. The escaping carbonic gas causes the asbestos fibres to be loosened and disintegrated from each other so as to render the ma.s.s porous. Of course it must be thoroughly washed with water before being used.
Again, in the purification of foul gas, as well as for ventilating and deodorizing man-holes for cesspools, sewers, &c., its use is found to be unsurpa.s.sed by any other known material.
Mr. Boyd, in the paper so often referred to, says in regard to this, that he was some time previously asked to supply asbestos yarn spun in such a way as to have good capillary action, and, on making inquiry, found it was to be used for the above purpose. In describing the mode of using it, he says that there is placed over the opening rising from the sewer a hood of galvanized wire, interlaced with this asbestos yarn, the ends of the yarn dipping into a receptacle filled with liquid disinfectant, which, as they become saturated, form a disinfecting screen, through the meshes of which the gases rise, and in their pa.s.sage through are purified and rendered innocuous. The system hitherto previously adopted for deodorizing sewer gas has been to cause it to rise through charcoal, but it is found that the impurities soon clog this up, and simply prevent the pa.s.sage of the gas, whereas in the arrangement just mentioned (which is that of Messrs. Adams & Co., of York), the gas rises freely, and is perfectly deodorized.
There are, of course, very numerous other applications of the material which might be referred to or described, but probably those already mentioned are the most important and the most interesting; and these, it is hoped, are at any rate sufficient to indicate the great value of this singular mineral product, as well as to confirm the statement with which I started, that this is indeed one of Nature"s most marvellous productions.
FOOTNOTES:
[10] There is a Patent Removable Covering now manufactured in New York which is said to be entirely formed of pure asbestos fibre, made in cylindrical sections of three-foot lengths of the exact size of the pipes to be covered. In this the asbestos fibres are so interlaced, that the sections, whilst possessing strength and flexibility, afford so large a number of air-cells as to give the covering the very highest non-conducting quality, whilst at the same time it cannot char or be in any way injured by the most intense heat from without or within. Fire Felt sectional coverings for boilers and large surfaces are made in convenient forms in sheets, &c. The same Company also manufacture what is called a Superator Jacket, both fire and waterproof, being in fact a flexible sheet of asbestos strengthened with wire netting, the asbestos being waterproofed by a special process, and provided with patent lacings, so that the jackets may be effectually kept in place, whilst being readily removable without cutting or loss of material.