Creative Chemistry: Descriptive of Recent Achievements in the Chemical Industries

by Edwin E. Slosson

I shoot the hippopotamus with bullets made of platinum,
Because if I use leaden ones, his hide is sure to flatten 'em.

Along in the latter half of the last century chemists had begun to perceive certain regularities and relationships among the various elements, so they conceived the idea that some sort of a pigeon-hole scheme might be devised in which the elements could be filed away in the order of their atomic weights so that one could see just how a certain element, known or unknown, would behave from merely observing its position in the series. Mendeléef, a Russian chemist, devised the most ingenious of such systems called the "periodic law" and gave proof that there was something in his theory by predicting the properties of three metallic elements, then unknown but for which his arrangement showed three empty pigeon-holes. Sixteen years later all three of these predicted elements had been discovered, one by a Frenchman, one by a German and one by a Scandinavian, and named from patriotic impulse, gallium, germanium and scandium. This was a triumph of scientific prescience as striking as the mathematical proof of the existence of the planet Neptune by Leverrier before it had been found by the telescope.

But although Mendeléef's law told "the truth," it gradually became evident that it did not tell "the whole truth and nothing but the truth," as the lawyers put it. As usually happens in the history of science the hypothesis was found not to explain things so simply and completely as was at first assumed. The anomalies in the arrangement did not disappear on closer study, but stuck out more conspicuously. Though Mendeléef had pointed out three missing links, he had failed to make provision for a whole group of elements since discovered, the inert gases of the helium-argon group. As we now know, the scheme was built upon the false assumptions that the elements are immutable and that their atomic weights are invariable.

The elements that the chemists had most difficulty in sorting out and identifying were the heavy metals found in the "rare earths." There were about twenty of them so mixed up together and so much alike as to baffle all ordinary means of separating them. For a hundred years chemists worked over them and quarreled over them before they discovered that they had a commercial value. It was a problem as remote from practicality as any that could be conceived. The man in the street did not see why chemists should care whether there were two didymiums any more than why theologians should care whether there were two Isaiahs. But all of a sudden, in 1885, the chemical puzzle became a business proposition. The rare earths became household utensils and it made a big difference with our monthly gas bills whether the ceria and the thoria in the burner mantles were absolutely pure or contained traces of some of the other elements that were so difficult to separate.

This sudden change of venue from pure to applied science came about through a Viennese chemist, Dr. Carl Auer, later and in consequence known as Baron Auer von Welsbach. He was trying to sort out the rare earths by means of the spectroscopic method, which consists ordinarily in dipping a platinum wire into a solution of the unknown substance and holding it in a colorless gas flame. As it burns off, each element gives a characteristic color to the flame, which is seen as a series of lines when looked at through the spectroscope. But the flash of the flame from the platinum wire was too brief to be studied, so Dr. Auer hit upon the plan of soaking a thread in the liquid and putting this in the gas jet. The cotton of course burned off at once, but the earths held together and when heated gave off a brilliant white light, very much like the calcium or limelight which is produced by heating a stick of quicklime in the oxy-hydrogen flame. But these rare earths do not require any such intense heat as that, for they will glow in an ordinary gas jet.

So the Welsbach mantle burner came into use everywhere and rescued the coal gas business from the destruction threatened by the electric light. It was no longer necessary to enrich the gas with oil to make its flame luminous, for a cheaper fuel gas such as is used for a gas stove will give, with a mantle, a fine white light of much higher candle power than the ordinary gas jet. The mantles are knit in narrow cylinders on machines, cut off at suitable lengths, soaked in a solution of the salts of the rare earths and dried. Artificial silk (viscose) has been found better than cotton thread for the mantles, for it is solid, not hollow, more uniform in quality and continuous instead of being broken up into one-inch fibers. There is a great deal of difference in the quality of these mantles, as every one who has used them knows. Some that give a bright glow at first with the gas-cock only half open will soon break up or grow dull and require more gas to get any kind of a light out of them. Others will last long and grow better to the last. Slight impurities in the earths or the gas will speedily spoil the light. The best results are obtained from a mixture of 99 parts thoria and 1 part ceria. It is the ceria that gives the light, yet a little more of it will lower the luminosity.

The non-chemical reader is apt to be confused by the strange names and their varied terminations, but he need not be when he learns that the new metals are given names ending in -um, such as sodium, cerium, thorium, and that their oxides (compounds with oxygen, the earths) are given the termination -a, like soda, ceria, thoria. So when he sees a name ending in -um let him picture to himself a metal, any metal since they mostly look alike, lead or silver, for example. And when he comes across a name ending in -a he may imagine a white powder like lime. Thorium, for instance, is, as its name implies, a metal named after the thunder god Thor, to whom we dedicate one day in each week, Thursday. Cerium gets its name from the Roman goddess of agriculture by way of the asteroid.

The chief sources of the material for the Welsbach burners is monazite, a glittering yellow sand composed of phosphate of cerium with some 5 per cent. of thorium. In 1916 the United States imported 2,500,000 pounds of monazite from Brazil and India, most of which used to go to Germany. In 1895 we got over a million and a half pounds from the Carolinas, but the foreign sand is richer and cheaper. The price of the salts of the rare metals fluctuates wildly. In 1895 thorium nitrate sold at $200 a pound; in 1913 it fell to $2.60, and in 1916 it rose to $8.

Since the monazite contains more cerium than thorium and the mantles made from it contain more thorium than cerium, there is a superfluity of cerium. The manufacturers give away a pound of cerium salts with every purchase of a hundred pounds of thorium salts. It annoyed Welsbach to see the cerium residues thrown away and accumulating around his mantle factory, so he set out to find some use for it. He reduced the mixed earths to a metallic form and found that it gave off a shower of sparks when scratched. An alloy of cerium with 30 or 35 per cent. of iron proved the best and was put on the market in the form of automatic lighters. A big business was soon built up in Austria on the basis of this obscure chemical element rescued from the dump-heap. The sale of the cerite lighters in France threatened to upset the finances of the republic, which derived large revenue from its monopoly of match-making, so the French Government imposed a tax upon every man who carried one. American tourists who bought these lighters in Germany used to be much annoyed at being held up on the French frontier and compelled to take out a license. During the war the cerium sparklers were much used in the trenches for lighting cigarettes, but—as those who have seen "The Better 'Ole" will know—they sometimes fail to strike fire. Auer-metal or cerium-iron alloy was used in munitions to ignite hand grenades and to blazon the flight of trailer shells. There are many other pyrophoric (light-producing) alloys, including steel, which our ancestors used with flint before matches and percussion caps were invented.

There are more than fifty metals known and not half of them have come into common use, so there is still plenty of room for the expansion of the science of metallurgy. If the reader has not forgotten his arithmetic of permutations he can calculate how many different alloys may be formed by varying the combinations and proportions of these fifty. We have seen how quickly elements formerly known only to chemists—and to some of them known only by name—have become indispensable in our daily life. Any one of those still unutilized may be found to have peculiar properties that fit it for filling a long unfelt want in modern civilization.