category of safe oils. The engine exhibited was very like an ordinary Otto gas-engine, and worked in exactly the same cycle. A pump at the side of the engine forced air into a small receiver at a few pounds pressure to the square inch. The compressed air, acting by means of a small injector, carried with it the oil in the form of fine spray, which issued into a jacketed chamber heated by the exhaust, in which the oil was vaporized. The mingled air and oil was thus raised to a temperature of about 300°, and was then drawn, with more air, into the cylinder, where, after being compressed by the return stroke of the piston, it was exploded by an electric spark, and at the end of the cycle the products of combustion were discharged into the air.after encircling the spray chamber and parting with most of their heat to the injected oil. The results of careful experiments made by Sir William Thomson and myself on different occasions were, that 1.73 pounds of petroleum were consumed per brake horse-power per hour; but the combustion was by no means perfect, for a sheet of paper held over the exhaust pipe was soon thickly spattered with spots of oil.

The enormous consumption of petroleum and of natural gases frequently raises the question as to the probability of the proximate exhaustion of the supply; and without doubt many fear to adopt the use of oil, from a feeling that if such use once becomes general the demand will exceed the production, the price will rise indefinitely, and old methods of illumination, and old forms of fuel, will have to be reverted to. From this point of view it is most interesting to inquire what are the probabilities of a continuous supply; and such an investigation leads at once to the question, "What is the origin of petroleum?" In the year 1877, Professor Mendeléef undertook to answer this question; and as his theory appears to be very little known, I trust you will forgive me for laying a matter so interesting before you. Dr. Mendeléef commences his essay by the statement that some persons assume (without any special reason excepting perhaps its chemical composition), that naphtha, like coal, has a vegetable origin. He combats this hypothesis, and points out, in the first place, that naphtha must have been formed in the depths of the earth. It could not have been produced on the sur

face, because it would have evaporated; nor over a sea bottom, because it would have floated up and been dissipated by the same means. In the next place he shows that naphtha must have been formed beneath the very site on which it is found,-that it can not have come from a distance, like so many other geological deposits, and for the reasons given above, namely, that it could not be water-borne, and could not have flowed along the surface, while in the superficial sands in which it is generally found no one has ever discovered the presence of organized matter in sufficiently large masses to have served as a source for the enormous quantity of oil and gas yielded in some districts; and hence it is most probable that it has risen from much greater depths under the influence of its own gaseous pressure, or floated up upon the surface of water, with which it is so frequently associated.

The process of the formation of petroleum seems to be the following: It is generally admitted that the crust of the earth is very thin in comparison with the diameter of the latter, and that this crust incloses soft or fluid substance, among which the carbides of iron and of other metals find a place. When, in consequence of cooling or some other cause, a fissure takes place through which a mountain range is protruded, the crust of the earth is bent, and at the foot of the hills fissures are formed; or at any rate the continuity of the rocky layers is disturbed, and they are rendered more or less porous, so that surface waters are able to make their way deep into the bowels of the earth, and to reach occasionally the heated deposits of metallic carbides, which may exist either in a separated condition or blended with other matter. Under such circumstances it is easy to see what must take place. Iron, or whatever other metal may be present, forms an oxide with the oxygen of the water; hydrogen is either set free or combined with the carbon which was associated with the metal, and becomes a volatile substance that is, naphtha. The water which had penetrated down to the incandescent mass was changed into steam, a portion of which found its way through the porous substances with which the fissures were filled, and carried with it the vapors of the newly-formed bydro-carbons, and this mixture of vapors was condensed wholly or in part as soon as it reached the cooler strata. The chemical composition of the hydro-carbons produced will depend upon the conditions of temperature and pressure under which they are formed. It is obvious that these may vary between very wide limits, and hence it is that mineral oils, mineral pitch, ozokerit, and similar products differ so greatly from each other in the relative proportions of hydrogen and carbon. I may mention that artificial petroleum has been frequently prepared by a process analogous to that described above.

It is needless to remark that Dr. Mendeléef's views are not shared by every competent authority; nevertheless, the remarkable permanence of oil-wells, the apparently inexhaustible evolution of hydro-carbon gases in certain regions, almost forces one to believe that the hydro-carbon products must be forming as fast as they are consumed, that there is little danger of the demand ever exceeding the supply, and that there is every prospect of oil being found in almost every portion of the surface of the earth, especially in the vicinity of great geological disturb ances. Improved methods of boring wells will enable greater depths to be reached; and it should be remembered that, apart from the cost of sinking a deep well, there is no extra expense in working at great depths, because the oil generally rises to the surface or near it. The extraordinary pressures, amounting to 300 pounds per square inch, which have been measured in some wells, seem to me to yield conclusive evidence of the impermeability of the strata from under which the oil has been forced up, and tend to confirm the view that it must have been formed in regions far below any which could have contained organic remains.

ALUMINUM.*

By H. C. HOVEY.

The formal opening of the great works of the Aluminum Brass and Bronze Company, at Bridgeport, Connecticut, makes it desirable, as a preliminary, that we state a few facts about the unalloyed metal itself. Quite learned men have indulged in wild talk about the metal, which is more widely distributed over the globe than any other, being known to exist in two hundred different minerals, including all granites and common clays.

The problem has been to extract the metal cheaply, and chemists of every land have labored for a solution. Ersted suggested a process of obtaining aluminum by treating the chloride with an alkali metal. Adopted by Woehler, and modified by Deville, the process was "a reduction of the double chloride of aluminum and sodium by means of metallic sodium in the presence of cryolite." It was thus that Deville was able to show at the Paris Exhibition in 1855, as the greatest of modern chemical wonders, a bar of what he styled "silver-white metal made from clay." He sold aluminum first at $15 an ounce, but in 1857 he reduced the price to $2 an ounce. Improvements cheapened the product still further, so that Colonel Frishmuth, who cast the tip of the Washington Monument in 1884, was able to furnish the metal in bars at $15 a pound. In that year however he made only 1,800 ounces, and the entire import was but 590 pounds.

Prior to 1887, the entire amount manufactured annually was but 10,000 pounds, and it sold that year at $10 a pound. To get even this small amount required the annual manufacture of 100,000 pounds of the double chloride and 40,000 pounds of sodium. To cheapen these two preliminary processes was essential to the cheap production of aluminum.

Hence the importance of the process patented by Mr. Hamilton Y. Castner, June 1, 1886, which was the first patent ever granted for an aluminum process in the United States. Its special feature was a cheap way of getting sodium. He reduced and distilled it in large iron crucibles, raised automatically through apertures in the bottom of the furnace, where they remain until the reduction is completed and the sodium * From the Scientific American. -46

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distilled. Through tubes in stationary covers the distilled metal passes to condensers, where it is solidified. When the process is completed, the crucible is lowered and a new one with a fresh charge is substituted and raised into the furnace. The residues are carbonate of soda and metallic iron, both of which can again be utilized. The process is as simple as it is ingenious, and the temperature required is very moderate, the sodium distilling as eazily as zinc. One charge requires about an hour, and a battery of four furnaces can yield a ton of sodium a day. The metal is kept from oxidation by a covering of mineral oil till used.

The Deville-Castner process takes the double chloride finely divided and mixed with thin slices of sodium, and empties the mixing cylinder on the hearth of a reverberatory furnace, where the mass quickly melts, and a re-action takes place that finally liberates a silvery stream of molten aluminum, that is drawn out from below, while the melted slag runs off from above. The first run is purest and contains about threefourths of the charge. The remainder is scraped off from the hearth, or found entangled with the slag, from which it has to be separated. The aluminum is finally re-melted in plumbago crucibles, and cast into ingots, bars, or plates.

The Journal of the Society of Arts, from whose very extended account the foregoing is abridged, adds that day by day, as the manufacture progresses, improvements are made which either enhance the economy of production or the purity of the product, and speaks in the highest praise of the skill, energy, and perseverance of Mr. Castner and his assistants, by whom, more than any others, aluminum has been brought into the market on commercially practicable terms and in a condition of almost perfect purity.

Grabau's process may be briefly described. Powdered cryolite put into a solution of the sulphate of aluminum gives by re-action the fluoride of aluminum, which is then heated till ready to evaporate. The heated fluoride is pulverized and thrown upon melted sodium contained in a vessel lined with cryolite. The heat generated by the violent re-action melts the aluminum as well as the cryolite; and the molten mass being poured out, the pure aluminum settles at the bottom, while the cryolite is at the top. The main advantage of this method over the Castner process is that it goes on at a lower temperature and is extremely simple. Numerous other processes are described by Richards in his exhaustive work on the subject; e. g., reduction by cyanogen, by hydrogen, by carburetted hydrogen, by carbon and carbon-dioxide, concerning all of which Dr. T. Sterry Hunt remarks that "there has been no pure aluminum made commercially save from the chloride by the use of sodium." Webster is the chief manufacturer in England on his own patents, and large works have been erected in France on Bunsen and Deville's process by electrolysis.

But after all, the only true rival of the Castner-Deville process seems to be the Hall process, on patents of Charles M. Hall, and carried on by

the Pittsourgh Reduction Company, who are now selling pure aluminum at a rate cheaper than nickel; and tons of metal are rolled by the Scoville Manufacturing Company, of Waterbury, into sheets, bars, rods, and tubing at a price less than German silver. Briefly, the Hall process is this: A flux being discovered that at a moderate temperature takes the aluminum ore into solution, and that is of lighter specific gravity, and that also is unaffected by the passage of an electric current, he fills a series of carbon-lined steel pots with the flux, which is kept in a melted condition. Carbon electrodes are plunged into these baths, through which passes the electric current, which acts to send the aluminum to the sides and bottom of each pot. The baths are constantly replenished with ore, and the process thus goes on for an indefinite period, night and day, at small cost, and demanding but little attention.

Aluminum, whether pure or in combination, deserves to rank with the noble metals;-although in certain forms it makes the basis of our common clay, every cubic yard of which is said to contain 800 pounds of the metal; in other forms it is massed in mountains; and in others still, it shines among the most precious stones, entering into the compo sition of the ruby, sapphire, topaz, garnet, lapis lazuli, and tourmaline. Cryolite, found in Greenland, and beauxite, first found at Beaux, in France, but since in Austria, Ireland, and elsewhere, are the ores relied on for the manufacture of aluminum. Cryolite is a snow-white mineral, though often tinged red or yellow by impurities. Beauxite is a hard white clay, occurring in beds many feet thick. Corundum, found in Georgia, is the material relied on in America especially for making the alloys. It varies from dull blue to black, and exists in massive form, well as in crystals. The cost at the factory of these different minerals varies from $60 to $140 a ton.

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The properties of aluminum are now generally known. Its color is white delicately tinged with blue, and it resembles silver more than any other metal. It takes a brilliant polish, and may be rolled or forged as easily as gold or silver, and may be beaten into very thin leaves. It can be pressed or stamped into all sorts of shapes, or drawn into very fine wire. Its elasticity and tenacity are about the same as virgin silver, but change greatly under the hammer. It is said to resist the graving-tool till properly varnished, when it may be cut like copper. Its sonorous. ness is very curious. Cast in bell form its sound is sharp, and not prolonged; but struck as a bar, it is remarkably sweet, pure, and resonant. Its sound is resolved into two tones, related to each other as are D and A. For a musical instrument, fine effects might be had from a series of chromatic bars.

In estimating the relative cost of aluminum as compared with other metals, we must take its specific gravity into the account. A bar of aluminum weighing 1 pound would be about four times as large as a simi lar bar of silver, brass, bronze, tin, or iron. Hence, at an equal price, aluminum would be four times as cheap as silver, but as it now costs by