Creative Chemistry Part 14

MAKING ALOXITE IN THE ELECTRIC FURNACES BY FUSING c.o.kE AND BAUXITE

In the background are the circular furnaces. In the foreground are the fused ma.s.ses of the product]

[Ill.u.s.tration: Courtesy of the Carborundum Co., Niagara Falls

A BLOCK OF CARBORUNDUM CRYSTALS]

[Ill.u.s.tration: Courtesy of the Carborundum Co., Niagara Falls

MAKING CARBORUNDUM IN THE ELECTRIC FURNACE

At the end may be seen the attachments for the wires carrying the electric current and on the side the flames from the burning carbon.]

The temperatures attainable with various fuels in the compound blowpipe are said to be:

Acetylene with oxygen 7878 F.

Hydrogen with oxygen 6785 F.

Coal gas with oxygen 6575 F.

Gasoline with oxygen 5788 F.

If we compare the formula of acetylene, C_{2}H_{2} with that of ethylene, C_{2}H_{4}, or with ethane, C_{2}H_{6}, we see that acetylene could take on two or four more atoms. It is evidently what the chemists call an "unsaturated" compound, one that has not reached its limit of hydrogenation. It is therefore a very active and energetic compound, ready to pick up on the slightest instigation hydrogen or oxygen or chlorine or any other elements that happen to be handy. This is why it is so useful as a starting point for synthetic chemistry.

To build up from this simple substance, acetylene, the higher compounds of carbon and oxygen it is necessary to call in the aid of that mysterious agency, the catalyst. Acetylene is not always acted upon by water, as we know, for we see it bubbling up through the water when prepared from the carbide. But if to the water be added a little acid and a mercury salt, the acetylene gas will unite with the water forming a new compound, acetaldehyde. We can show the change most simply in this fas.h.i.+on:

C_{2}H_{2} + H_{2}O --> C_{2}H_{4}O

acetylene _added to_ water _forms_ acetaldehyde

Acetaldehyde is not of much importance in itself, but is useful as a transition. If its vapor mixed with hydrogen is pa.s.sed over finely divided nickel, serving as a catalyst, the two unite and we have alcohol, according to this reaction:

C_{2}H_{4}O + H_{2} --> C_{2}H_{6}O

acetaldehyde _added to_ hydrogen _forms_ alcohol

Alcohol we are all familiar with--some of us too familiar, but the prohibition laws will correct that. The point to be noted is that the alcohol we have made from such unpromising materials as limestone and coal is exactly the same alcohol as is obtained by the fermentation of fruits and grains by the yeast plant as in wine and beer. It is not a subst.i.tute or imitation. It is not the wood spirits (methyl alcohol, CH_{4}O), produced by the destructive distillation of wood, equally serviceable as a solvent or fuel, but undrinkable and poisonous.

Now, as we all know, cider and wine when exposed to the air gradually turn into vinegar, that is, by the growth of bacteria the alcohol is oxidized to acetic acid. We can, if we like, dispense with the bacteria and speed up the process by employing a catalyst. Acetaldehyde, which is halfway between alcohol and acid, may also be easily oxidized to acetic acid. The relations.h.i.+p is readily seen by this:

C{2}H_{6}O --> CC_{2}H_{4}O --> C_{2}H_{4}O_{3}

alcohol acetaldehyde acetic acid

Acetic acid, familiar to us in a diluted and flavored form as vinegar, is when concentrated of great value in industry, especially as a solvent. I have already referred to its use in combination with cellulose as a "dope" for varnis.h.i.+ng airplane canvas or making non-inflammable film for motion pictures. Its combination with lime, calcium acetate, when heated gives acetone, which, as may be seen from its formula (C_{3}H_{6}O) is closely related to the other compounds we have been considering, but it is neither an alcohol nor an acid. It is extensively employed as a solvent.

Acetone is not only useful for dissolving solids but it will under pressure dissolve many times its volume of gaseous acetylene. This is a convenient way of transporting and handling acetylene for lighting or welding.

If instead of simply mixing the acetone and acetylene in a solution we combine them chemically we can get isoprene, which is the mother substance of ordinary India rubber. From acetone also is made the "war rubber" of the Germans (methyl rubber), which I have mentioned in a previous chapter. The Germans had been getting about half their supply of acetone from American acetate of lime and this was of course shut off. That which was produced in Germany by the distillation of beech wood was not even enough for the high explosives needed at the front. So the Germans resorted to rotting potatoes--or rather let us say, since it sounds better--to the cultivation of _Bacillus macerans_. This particular bacillus converts the starch of the potato into two-thirds alcohol and one-third acetone. But soon potatoes got too scarce to be used up in this fas.h.i.+on, so the Germans turned to calcium carbide as a source of acetone and before the war ended they had a factory capable of manufacturing 2000 tons of methyl rubber a year. This shows the advantage of having several strings to a bow.

The reason why acetylene is such an active and acquisitive thing the chemist explains, or rather expresses, by picturing its structure in this shape:

H-C[triple bond]C-H

Now the carbon atoms are holding each other's hands because they have nothing else to do. There are no other elements around to hitch on to.

But the two carbons of acetylene readily loosen up and keeping the connection between them by a single bond reach out in this fas.h.i.+on with their two disengaged arms and grab whatever alien atoms happen to be in the vicinity:

| | H-C-C-H | |

Carbon atoms belong to the quadrumani like the monkeys, so they are peculiarly fitted to forming chains and rings. This accounts for the variety and complexity of the carbon compounds.

So when acetylene gas mixed with other gases is pa.s.sed over a catalyst, such as a heated ma.s.s of iron ore or clay (hydrates or silicates of iron or aluminum), it forms all sorts of curious combinations. In the presence of steam we may get such simple compounds as acetic acid, acetone and the like. But when three acetylene molecules join to form a ring of six carbon atoms we get compounds of the benzene series such as were described in the chapter on the coal-tar colors. If ammonia is mixed with acetylene we may get rings with the nitrogen atom in place of one of the carbons, like the pyridins and quinolins, pungent bases such as are found in opium and tobacco. Or if hydrogen sulfide is mixed with the acetylene we may get thiophenes, which have sulfur in the ring. So, starting with the simple combination of two atoms of carbon with two of hydrogen, we can get directly by this single process some of the most complicated compounds of the organic world, as well as many others not found in nature.

In the development of the electric furnace America played a pioneer part. Provost Smith of the University of Pennsylvania, who is the best authority on the history of chemistry in America, claims for Robert Hare, a Philadelphia chemist born in 1781, the honor of constructing the first electrical furnace. With this crude apparatus and with no greater electromotive force than could be attained from a voltaic pile, he converted charcoal into graphite, volatilized phosphorus from its compounds, isolated metallic calcium and synthesized calcium carbide. It is to Hare also that we owe the invention in 1801 of the oxy-hydrogen blowpipe, which nowadays is used with acetylene as well as hydrogen.

With this instrument he was able to fuse strontia and volatilize platinum.

But the electrical furnace could not be used on a commercial scale until the dynamo replaced the battery as a source of electricity. The industrial development of the electrical furnace centered about the search for a cheap method of preparing aluminum. This is the metallic base of clay and therefore is common enough. But clay, as we know from its use in making porcelain, is very infusible and difficult to decompose. Sixty years ago aluminum was priced at $140 a pound, but one would have had difficulty in buying such a large quant.i.ty as a pound at any price. At international expositions a small bar of it might be seen in a case labeled "silver from clay." Mechanics were anxious to get the new metal, for it was light and untarnishable, but the metallurgists could not furnish it to them at a low enough price. In order to extract it from clay a more active metal, sodium, was essential. But sodium also was rare and expensive. In those days a professor of chemistry used to keep a little stick of it in a bottle under kerosene and once a year he whittled off a piece the size of a pea and threw it into water to show the cla.s.s how it sizzled and gave off hydrogen. The way to get cheaper aluminum was, it seemed, to get cheaper sodium and Hamilton Young Castner set himself at this problem. He was a Brooklyn boy, a student of Chandler's at Columbia. You can see the bronze tablet in his honor at the entrance of Havemeyer Hall. In 1886 he produced metallic sodium by mixing caustic soda with iron and charcoal in an iron pot and heating in a gas furnace. Before this experiment sodium sold at $2 a pound; after it sodium sold at twenty cents a pound.

But although Castner had succeeded in his experiment he was defeated in his object. For while he was perfecting the sodium process for making aluminum the electrolytic process for getting aluminum directly was discovered in Oberlin. So the $250,000 plant of the "Aluminium Company Ltd." that Castner had got erected at Birmingham, England, did not make aluminum at all, but produced sodium for other purposes instead. Castner then turned his attention to the electrolytic method of producing sodium by the use of the power of Niagara Falls, electric power. Here in 1894 he succeeded in separating common salt into its component elements, chlorine and sodium, by pa.s.sing the electric current through brine and collecting the sodium in the mercury floor of the cell. The sodium by the action of water goes into caustic soda. Nowadays sodium and chlorine and their components are made in enormous quant.i.ties by the decomposition of salt. The United States Government in 1918 procured nearly 4,000,000 pounds of chlorine for gas warfare.

The discovery of the electrical process of making aluminum that displaced the sodium method was due to Charles M. Hall. He was the son of a Congregational minister and as a boy took a fancy to chemistry through happening upon an old text-book of that science in his father's library. He never knew who the author was, for the cover and t.i.tle page had been torn off. The obstacle in the way of the electrolytic production of aluminum was, as I have said, because its compounds were so hard to melt that the current could not pa.s.s through. In 1886, when Hall was twenty-two, he solved the problem in the laboratory of Oberlin College with no other apparatus than a small crucible, a gasoline burner to heat it with and a galvanic battery to supply the electricity. He found that a Greenland mineral, known as cryolite (a double fluoride of sodium and aluminum), was readily fused and would dissolve alumina (aluminum oxide). When an electric current was pa.s.sed through the melted ma.s.s the metal aluminum would collect at one of the poles.

In working out the process and defending his claims Hall used up all his own money, his brother's and his uncle's, but he won out in the end and Judge Taft held that his patent had priority over the French claim of Herault. On his death, a few years ago, Hall left his large fortune to his Alma Mater, Oberlin.

Two other young men from Ohio, Alfred and Eugene Cowles, with whom Hall was for a time a.s.sociated, wore the first to develop the wide possibilities of the electric furnace on a commercial scale. In 1885 they started the Cowles Electric Smelting and Aluminum Company at Lockport, New York, using Niagara power. The various aluminum bronzes made by absorbing the electrolyzed aluminum in copper attracted immediate attention by their beauty and usefulness in electrical work and later the company turned out other products besides aluminum, such as calcium carbide, phosphorus, and carborundum. They got carborundum as early as 1885 but miscalled it "crystallized silicon," so its introduction was left to E.A. Acheson, who was a graduate of Edison's laboratory. In 1891 he packed clay and charcoal into an iron bowl, connected it to a dynamo and stuck into the mixture an electric light carbon connected to the other pole of the dynamo. When he pulled out the rod he found its end encrusted with glittering crystals of an unknown substance. They were blue and black and iridescent, exceedingly hard and very beautiful. He sold them at first by the carat at a rate that would amount to $560 a pound. They were as well worth buying as diamond dust, but those who purchased them must have regretted it, for much finer crystals were soon on sale at ten cents a pound. The mysterious substance turned out to be a compound of carbon and silicon, the simplest possible compound, one atom of each, CSi. Acheson set up a factory at Niagara, where he made it in ten-ton batches. The furnace consisted simply of a brick box fifteen feet long and seven feet wide and deep, with big carbon electrodes at the ends. Between them was packed a mixture of c.o.ke to supply the carbon, sand to supply the silicon, sawdust to make the ma.s.s porous and salt to make it fusible.

[Ill.u.s.tration: The first American electric furnace, constructed by Robert Hare of Philadelphia. From "Chemistry in America," by Edgar Fahs Smith]

The substance thus produced at Niagara Falls is known as "carborundum"

south of the American-Canadian boundary and as "crystolon" north of this line, as "carbolon" by another firm, and as "silicon carbide" by chemists the world over. Since it is next to the diamond in hardness it takes off metal faster than emery (aluminum oxide), using less power and wasting less heat in futile fireworks. It is used for grindstones of all sizes, including those the dentist uses on your teeth. It has revolutionized shop-practice, for articles can be ground into shape better and quicker than they can be cut. What is more, the artificial abrasives do not injure the lungs of the operatives like sandstone. The output of artificial abrasives in the United States and Canada for 1917 was:

Tons Value Silicon carbide 8,323 $1,074,152 Aluminum oxide 48,463 6,969,387

A new use for carborundum was found during the war when Uncle Sam a.s.sumed the role of Jove as "cloud-compeller." Acting on carborundum with chlorine--also, you remember, a product of electrical dissolution--the chlorine displaces the carbon, forming silicon tetra-chloride (SiCl_{4}), a colorless liquid resembling chloroform.

When this comes in contact with moist air it gives off thick, white fumes, for water decomposes it, giving a white powder (silicon hydroxide) and hydrochloric acid. If ammonia is present the acid will unite with it, giving further white fumes of the salt, ammonium chloride. So a mixture of two parts of silicon chloride with one part of dry ammonia was used in the war to produce smoke-screens for the concealment of the movements of troops, batteries and vessels or put in sh.e.l.ls so the outlook could see where they burst and so get the range.

t.i.tanium tetra-chloride, a similar substance, proved 50 per cent. better than silicon, but phosphorus--which also we get from the electric furnace--was the most effective mistifier of all.

Before the introduction of the artificial abrasives fine grinding was mostly done by emery, which is an impure form of aluminum oxide found in nature. A purer form is made from the mineral bauxite by driving off its combined water. Bauxite is the ore from which is made the pure aluminum oxide used in the electric furnace for the production of metallic aluminum. Formerly we imported a large part of our bauxite from France, but when the war shut off this source we developed our domestic fields in Arkansas, Alabama and Georgia, and these are now producing half a million tons a year. Bauxite simply fused in the electric furnace makes a better abrasive than the natural emery or corundum, and it is sold for this purpose under the name of "aloxite," "alundum," "exolon," "lionite"

or "coralox." When the fused bauxite is worked up with a bonding material into crucibles or m.u.f.fles and baked in a kiln it forms the alundum refractory ware. Since alundum is porous and not attacked by acids it is used for filtering hot and corrosive liquids that would eat up filter-paper. Carborundum or crystolon is also made up into refractory ware for high temperature work. When the fused ma.s.s of the carborundum furnace is broken up there is found surrounding the carborundum core a similar substance though not quite so hard and infusible, known as "carborundum sand" or "siloxicon." This is mixed with fireclay and used for furnace linings.

Many new forms of refractories have come into use to meet the demands of the new high temperature work. The essentials are that it should not melt or crumble at high heat and should not expand and contract greatly under changes of temperature (low coefficient of thermal expansion).

Whether it is desirable that it should heat through readily or slowly (coefficient of thermal conductivity) depends on whether it is wanted as a crucible or as a furnace lining. Lime (calcium oxide) fuses only at the highest heat of the electric furnace, but it breaks down into dust.

Magnesia (magnesium oxide) is better and is most extensively employed.

For every ton of steel produced five pounds of magnesite is needed.

Formerly we imported 90 per cent. of our supply from Austria, but now we get it from California and Was.h.i.+ngton. In 1913 the American production of magnesite was only 9600 tons. In 1918 it was 225,000. Zirconia (zirconium oxide) is still more refractory and in spite of its greater cost zirkite is coming into use as a lining for electric furnaces.

Silicon is next to oxygen the commonest element in the world. It forms a quarter of the earth's crust, yet it is unfamiliar to most of us. That is because it is always found combined with oxygen in the form of silica as quartz crystal or sand. This used to be considered too refractory to be blown but is found to be easily manipulable at the high temperatures now at the command of the gla.s.s-blower. So the chemist rejoices in flasks that he can heat red hot in the Bunsen burner and then plunge into ice water without breaking, and the cook can bake and serve in a dish of "pyrex," which is 80 per cent. silica.

At the beginning of the twentieth century minute specimens of silicon were sold as laboratory curiosities at the price of $100 an ounce. Two years later it was turned out by the barrelful at Niagara as an accidental by-product and could not find a market at ten cents a pound.