Aluminum is fast becoming an important article of commerce, and it is destined to become more and more so on account of its extreme lightness as compared to other metals.
It is found to be valuable also when used as an alloy with many of the other metals. One of the great drawbacks to its more extensive use lies in the fact that as yet no satisfactory method has been devised for soldering it. Undoubtedly in time this difficulty will be solved, when its use will be greatly increased. It is estimated that in its various compounds aluminum forms about one-twelfth of the crust of the earth.
CHAPTER XXVIII.
ELECTRICAL PRODUCTS—CALCIUM CARBIDE.
Another important use to which electricity is put at Niagara Falls is the manufacture of a new product, called calcium carbide. Like carborundum and aluminum, this product could not have been produced in commercial quantities in advance of a means for producing electricity in enormous volume.
Calcium carbide is a compound of calcium and carbon. Calcium is a white metal not found in the natural state, but exists chiefly as a carbonate of lime, which is ordinary limestone, including the various forms of marble. As a pure metal it is hard to obtain and very hard to maintain, as it readily oxidizes when in contact with the air. The symbol for calcium carbide is CaC2, which means that a molecule of this carbide is compounded of one atom of calcium and two atoms of carbon. Ca stands for calcium and C for carbon. When the symbol has no figure following it, it means that one atom only enters into the compound; but if a figure follows, it means that as many atoms enter in as the figure represents.
The process of manufacturing calcium carbide is as follows: Ordinary lime before it is slacked is ground to a fine powder; then it is mixed with powdered coke or carbon in the proper quantities, so that when a chemical union takes place the proportion will be as before stated, one atom of calcium to two of carbon. As is well known, lime is procured by exposing ordinary limestone to a red heat for some hours together. The heat disengages the carbon dioxide, leaving only a combination of calcium and oxygen, which is common lime.
The mixture of ground lime and coke is put into a crucible that surrounds the arc of an electric light of enormous dimensions; the carbon conductors amounting to an area of one square foot or more. In order to cause the carbon to unite with the calcium a very intense heat is required, such a heat as can be obtained only in the arc of an electric light. When the enormous current is turned on (amounting to over 3000 horse-power) the mixture is melted, and after an exposure to this intense heat for a given length of time the oxygen of the unslacked lime is thrown off and the carbon unites with the calcium, which remains in the proportions of one atom of calcium to two of carbon, as before stated. This, it will be noted, is purely a heat process, and an intense one at that. No electrolytic action being required, the alternating current is used without transformation to the direct current, as is necessary in the manufacture of bleaching-powder and aluminum, both of which are electrolytic processes.