Popular Science Monthly/Volume 36/February 1890/Canadian Asbestus: Its Occurrence and Uses
|CANADIAN ASBESTUS: ITS OCCURRENCE AND USES.|
ASBESTUS is a singular mineral, whose characteristics are well indicated in the various names by which it is known. The French Canadian miners call it pierre à coton i. e., cotton-stone. The Germans speak of it as Steinflachs, stone-flax; and amianto, the Italian name, indicates that which is undefiled, in allusion to the fact that it may be cleansed by fire. Asbestus, the name by which it is generally known, is a Greek word, signifying endless, ceaseless, and points to its fire-resisting properties.
Asbestus is, then, a mineral occurring in a fibrous form, the fibers being so fine and flexible that they may be spun and woven as cotton and flax are; and, moreover, the fabric so obtained is capable of resisting a very high temperature. Some varieties are said to have resisted a temperature of 5,000° Fahr. It must be noted, however, that although this mineral is infusible, except at extremely high temperatures, its fibers lose their flexibility and become brittle at a temperature only sufficiently high to deprive it of the water which forms a part of its composition.
By the mineralogist the term asbestus was originally applied to a finely fibrous form of hornblende; but, as Dana adds, much that is so called is a fibrous form of serpentine. Most if not all the asbestus of commerce is fibrous serpentine. A recent analysis made in the writer's laboratory showed the following composition:
|Oxide of iron||2·41||"|
This mineral has been known from very early times, but it is only within recent years that it has found any extensive application in the various industrial arts. In ancient Greece the bodies of those who were to be burned upon the funeral pyre were wrapped in asbestus cloth, that their ashes might be kept separate from those of the pyre. In the eighth century Charlemagne is said to have had an asbestus table-cloth, with which, when the feast was over, he was wont to amuse his rude warrior guests by throwing it into the fire, and in a short time withdrawing it cleansed and uninjured.
On the other hand, the first Canadian deposit was opened only in 1878, and the owners experienced considerable difficulty in disposing of their output, which for the season did not exceed fifty tons. In 1889, with a Canadian output for the year of nearly five thousand tons, the demand is in excess of the supply, and is increasing, with prices showing an upward tendency.
The asbestus of commerce is the product of two widely separated countries—Italy and Canada. The Italian article was first in the market, but the Canadian product soon made for itself a place and a name, and the mineral is now shipped from Canada to Italy; while toward the close of 1889 the United Asbestus Company, Limited, of London, England, which controls the Italian mines, acquired property in the Canadian field, and is equipping the same with a complete plant preparatory to operations on a large scale. It is very evident, then, that the Canadian fiber is, to say the least, no mean factor in the asbestus industry.
Canadian asbestus occurs in serpentine, being, as already explained, a fibrous form of this mineral. In two great geological formations represented in Canada there are extensive areas of serpentine, viz.—the Laurentian, which, beginning on the coast of Labrador, stretches westward beyond the Great Lakes; and the Quebec Group, a formation occupying a large portion of the province of Quebec lying between the river St. Lawrence and the United States boundary. In the serpentine of both these formations asbestus occurs, but as yet it has not been proved that the asbestus veins of the Laurentian serpentines are sufficiently persistent to warrant mining operations. It is not improbable that productive areas may yet be found in the Laurentian rock, as prospectors are now turning attention in this direction. But at present it is only in the serpentine of the Quebec Group that productive mining is carried on.
In this formation there is a belt of serpentine rock "which extends with tolerable directness, though with frequent breaks, northeastward from the Vermont boundary to some distance beyond the Chaudière River," which flows into the St. Lawrence near the city of Quebec. Throughout the whole of this belt there are indications of the occurrence of asbestus, but the present productive area comprises only a very small portion of this extensive belt. Although good workings occur elsewhere, the great majority of the mines are along the line of the Quebec Central Railway, which runs from the city of Quebec to Sherbrooke, the capital of the so-called Eastern Townships of Canada, and cluster around two points a short distance apart and about midway between the two cities. In this district the serpentine forms a very rugged country, rising into bold peaks and ridges, the ruggedness and boldness being enhanced by numerous faults and dislocations of the rock. Bush-fires have recently passed over much of it, and the partially burned trees, with the scarred and seamed rocks as a back-ground, constitute a somewhat drear and dismal scene.
In the serpentine the asbestus forms irregular veins, varying from mere threads to four, six, and occasionally even more inches in width. The fiber is always at right angles to the sides of the vein, unless thrown otherwise as a result of faults. In some cases the mineral has been found concentrated in pockets, from which several tons have been taken. The color of the asbestus in the veins is white, greenish, or yellow, but near the surface the veins are frequently more or less discolored from infiltration through the shattered rock of water carrying oxide of iron. At a depth, and where solid rock is reached, this trouble usually ceases. The asbestus veins are frequently traversed by bands of foreign matter, such as compact serpentine, chromic and magnetic iron, and these, of course, lessen the value of the veins in which, they occur, since they cut up the fiber and must be removed at considerable trouble.
Associated with the asbestus one usually finds a considerable quantity of coarsely fibrous mineral, for which, as yet, no use has been found, together with foliated and slaty forms of serpentine. Some of the latter are of very singular appearance. To use the words of an English gentleman who spent some time in the Canadian asbestus region, "Many of these fragments, as they lie on the ground after blasting, have so much the appearance of a wood-cutter's choppings that, if placed side by side with actual choppings from rough timber, exposed to the weather, the one could in no way be distinguished from the other except, of course, by handling." Others, again, in color and shape very much resemble strips of fancy confectionery.
Still another singular associate of the asbestus is a mineral of a white or green or yellow color, occurring in thin veins. When first exposed it is so soft that it may be easily indented by the finger-nail, but on contact with the air it soon hardens and assumes an appearance somewhat like porcelain. Analysis shows it to be closely related to serpentine.
Mining is carried on by cutting down the hills of asbestus-bearing serpentine, much as a farmer cuts down a stack of hay or straw, or by open quarrying on the level. The rock is blasted out and the asbestus, separated from the containing rock, is "cobbed"—i.e., separated by hammering from adhering foreign matter. This "cobbing" is a comparatively easy matter in the case of the finer quality, as it usually separates readily from the gangue, but in the lower grades much difficulty is experienced in separating the fibrous matter from the non-fibrous. At best there is great waste. Much of the asbestus is in thin or narrow veins, and is wasted, as by the present mode of operating it does not pay to separate this from the serpentine. A machine that will enable these narrow veins to be utilized is a desideratum.
When "cobbed" the asbestus is graded according to purity, color, and length of fiber into three grades and bagged for shipment. The finest quality or "firsts" finds ready sale at prices ranging from $80 to $110 per ton; "seconds" fetch from $50 to $70 per ton; while "thirds" may be valued at $13 to $15 per ton. In good mines the yield of asbestus is from three to five per cent of the rock quarried, and the cost of mining may be put down at $25 to $30 per ton. Returns obtained by the Geological Survey of Canada show that, for the year 1888, Canada's output was 4,404 tons, valued at the mines at $255,000, and this the output of nine different mines. Over three fourths of the whole was shipped to the United States; small quantities going to Great Britain, Germany, France, Belgium, and Italy, and being used in domestic manufacturing.
Judging from the results obtained in the mines now worked, and the indications in other parts of the serpentine belt, it may be safely said that the asbestus deposits of Canada are well-nigh inexhaustible. There is every prospect that the industry will rapidly expand, as capitalists are turning attention to it, the work hitherto done "proving conclusively that mining for asbestus, when properly conducted, shows a more steady return for the money invested, with less elements of risk, than mining for any other known mineral."
Upon its non-conducting power and its ability to resist high temperature depend the many varied uses of the mineral. First and most important are its applications in connection with the steam engine and boiler. For packing pistons, flange joints, hot-air joints, cylinder-heads, and similar purposes, asbestus has proved itself invaluable, and for these purposes it is spun into yarn or wicking or rope, or made into mill-board. A large quantity is manufactured into a kind of felt, either alone or, in some cases, along with other fibrous material. Much of this asbestus felt is used as a non-conducting covering for steam-pipes. It is made into sections to fit any size of pipe, and into rolls and sheets for large surfaces. It is in use on the war-ships of the United States Navy, and has there and elsewhere been demonstrated to be superior to hair-felt as a non-conductor. By preventing radiation of heat from steam and hot-air pipes, this felt effects a large saving in fuel and gives dry steam at long distances from the boiler, and, by preventing excessive warmth of the boiler-house, adds much to the comfort of the workmen. The felt also finds application as a sheathing for covering wood-work in positions exposed to heat, and for fire-proofing flooring, shelving, partitions, and the like.
As far back as 1850 the Chevalier Aldini of Milan, experimented with asbestus, mainly with the object of turning it to account in the manufacture of asbestus cloth, but little success was met with until twenty years later. The unctuous character of the substance and the extreme fineness of the ultimate fiber are obstacles in the way of making asbestus cloth that shall be strongly coherent and not pull asunder easily. These difficulties appear to have been overcome to a great extent, and now in the form of woven fabrics there are many important applications of asbestus. To one of these, in particular, the attention of the public is frequently directed, because of the numerous fatal fires reported in theatres, music-halls, and similar places of entertainment. In the great majority of theatre fires the flames begin in the stage curtains or drapery. When these are made of asbestus, of course they are incombustible; or, if the curtain alone be of asbestus it affords a means of separating the stage from the body of the theatre, and, in case of fire in the former, prevents its spread to the auditorium. Asbestus curtains are now in use in the principal Roman theatres, and in many theatres in German, English, and American cities, much to the advantage of the theatre-going public. The mineral is also made into gloves, stockings, and other garments; in fact, complete suits of asbestus clothing can be obtained. In Paris the firemen of the city have recently been furnished with entire suits of asbestus cloth, and it is said to be probable that London will soon follow the example of the French capital.
In the form of gloves it is of much service to stokers and furnace-men, and as salvage blankets it is of great value. It is announced that mail-bags will, in the near future, be of asbestus. The frequent loss of mail matter by fire, in connection with railway accidents, renders it desirable that some incombustible material be used for this purpose.
Much of the lower grade of asbestus is ground up with other materials and made into cement and paint. The former is extensively used as a non-conducting covering for boilers and steam-pipes. Being a cement, it can not be readily removed without much labor and loss, so that it is somewhat less convenient than the felt, which, as already mentioned, is used for the same purpose. It is, however, very much cheaper; and this, in the estimation of many, more than compensates for the less convenient form. Certain it is that much more cement than felt is used as a non-conducting covering.
The paint finds extensive application; a layer of it, while not rendering a wooden surface absolutely fire-proof, is yet proof against sparks and slight flames, and thus prevents the spread and increase of many an incipient fire.
In the form of rope it is used in the construction of fire-escapes and supports that may have to withstand fire. We have also asbestus paper. As a wall-paper it aids in rendering a building fire-proof. In the form of writing and printing paper it presents a fire-proof paper that may be used in valuable legal and commercial documents.
Not only does our mineral resist high temperatures, but it is also proof against the action of the majority of chemicals. It therefore forms a very valuable substance for use in filtering apparatus, especially where acid and alkaline liquids which corrode ordinary filtering paper and cloth have to be dealt with. As a filtering medium it is used not only in chemical laboratories, but in manufacturing establishments as well.
Though the asbestus industry is only in its infancy, many other uses might be mentioned; but, bearing in mind that it is possible to produce from it fire-proof fabrics of any form or shape, there will readily occur to the mind of the reader many other possible applications of this curious product of Nature's laboratory which has waited so long for an opportunity to minister to the comfort, convenience, and safety of man.