; P we& 8th New England Association of Chem
C. R. Hammondl
Emhart Manufacturing Co. Hartford, Connecticut
chers
Collecting the Chemical Elements
A n y person who scans the advertising pages of the current technical magazines in the physical sciences cannot fail to be impressed by the increasing number of chemical elements that once were considered rare but today are commercially available, in quantity, with a high degree of purity. One bit of information these advertisements do not often provide, however, is the price. The enthusiasm of a scientist with a limited budget toward the use of an exotic element may well be shattered when he learns that the price of the form he needs is $100 per gram, with a minimum order of 10 grams, and delivery several weeks away. With the vast sums being spent on space research, there can be no doubt that much of the glamour is off the once-rare elements. We now hear of workers in local defense plants who are regularly machining large ingots of beryllium, or are using germanium, niobium, or indium for space vehicle applications. I n spite of this, there are still many chemistry and physics teachers who have yet to lay their eyes on an elemental piece of common lithium, calcium, boron, or strontium. Only a few have ever seen, let alone handled, scandium, europium, lutetium, or rhenium in their pure states. Like many other students, when the author was first introduced to chemistry a number of years ago, he attempted to make an element collection as a science project. After considerable effort about 25 elements were assembled, a t which point the project abruptly ended. Yo new sources of supply could be found, and the remaining elements that might have been obtained were fantastically rare and expensive. Further interest in the collection lay dormant until about two years ago. Then it was realized that now, for the first time, it might be possible to complete or to enlarge greatly the set a t a moderate cost. Such a collection would make an interesting exhibit for an astronomy course the author has been teaching for several years. I n this course, considerable attention is given to the cosmological abundance of the elements, for this sub,ject has great bearing on the problem of the creation of the solar system and the universe. We know that hydrogen accounts for about 76% of the mass of the universe, helium for a little less than 23%, and all the 1 Manager of Library, Emhart Mfg. Co., and Adjunct Instruc+or of Astronomy, University of Hartford, Hartford, Conn.
other elements for only a little more than ITo. Some of the elements of higher atomic weight that are rare on an earthly scale are rare beyond imagination on a cosmological scale. On our planet we are indeed fortunate to have (or to have had) samples-though some are very minute--of almost every one of the known 103 chemical elements. There are probably few stars or planets in the universe that could boast of this fact. Making the Collection
Just how many elements could be assembled could not be ascertained without making the attempt,? but the author thought that it might be possible for h i to show his students a collection of more than 70 elements. This would be several more than the number so far identified in the sun, the supposed parent of the earth. It was decided, tentatively, that whenever possible, a t least one gram of the element would be obtained. However, it was realized that in some cases, because of cost and rarity, it would be necessary to settle for much less. After some 18 months of correspondence with suppliers, the end of the trail has again been reached. This time, however, the collection contains appreciable amounts of some 86 elements, 83 of which are in isolated form. It would be possible to add several more isolated elements or compounds containing them, but AEC permits would be required, and the substances would be expensive, radioactively unstable, toxic, or generally dangerous for a small exhibit. It was therefore decided to stop the project a t this point. Much of the time required for making the collection was spent going down blind alleys or trying to locate sup~ l i e r who s would furnish minimum amounts so that the cost would not get out of hand. There is no doubt that such a collection could have been made in a fraction of The Museum of Science and Industry in Chicago has in its Hall of Elements 70 isolated elements. It haa recently been learned that plans are being made to enlarge the collection. This collection was originally made in 1933 for the Century of Progress Expositionby the late Dr. Henry Crew and Dr. Irving E. Muskat. The U.S. Atomic Energy Commission through the Oak Ridge National Laboratory produces and offers to licensed customers more than 300 different isotopes of some 55 elements. It is doubb ful, however, that these have ever heen assembled or arranged as a collection for educational purposes. Volume 4 1, Number 7, July 1964
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the time taken had unlimited funds been available. It was easier, for example, to find a supplier who would furnish hafnium in 100-lb quantities, than it was to find one who would supply it in one-gram lots. Many suppliers will not accept an order for less than $50 or they have added service charges that make the cost of small quantities unreasonable. However, by careful selection of sources, it was possible to keep the cost of the collection down to a m o d s t amount-about $250. It is not possible to list the sources of supply hem, for some elements were the kind donations of various individuals and companies; others were furnished only as a courtesy of the ~ u p p l i e r . ~ Some Facts and Figurer
The collection, shown in Figure 1, fits neatly into a small box that is easily transported. Because of the interest of audiences to which it has been displayed, some potentially useful notes and observations concerning the unconmlon elements and their compounds are presented here. It is hoped that these notes may help others who are interested in making similar collections or in acquiring a given element.
Figure 1 .
Collecfion of 'hemirol elements.
Hydrogen (Deuterium). Deuterium gas (99.5y0) is readily available without an AEC permit a t a cost of about $1 per gram plus container charge. Heavy water, the oxide of deuterium, is also available without permit a t prices ranging from 12 to 95C per gram, depending on quantity. Five grams of heavy water are included in the collection. Rubidium and Cesium. Both of these elements are available at about 83 to 7 per gram in evacuated, sealed ampoules. They should not be exposed to air for they rapidly oxidize and may ignite. Rubidium contains about 28% of a naturally occurring radioactive isotope, which is a sufficiently strong source of radiation to produce a radiograph of itself in 3-6 months. Francium. l'rancinm, missing from the collection, has the distinction of being the most unstable of all the a The author can supply more detailed information on sources of supply t o readers who request it. A stamped self-addressed envelope should be provided. Correspondence should be directed to Mr. C. R. Hammond, 17 Greystone Rd., West Hartford 7, Conn.
elements, up to californium (at. no. 98). The half life of its longest-lived isotope is only 21 min. Beryllium. I n small quantities, beryllium may cost anywhere from 50b per gram in ingot form to 9640 per gram in sheet form. Special handling must be provided, for this element is toxic in very small quantities to certain sensitive individuals. It is considered to be one of the most toxic in the collection. Radium. I n the isolated form, this element is probably ]lot commercially available anywhere in the world. As radium bromide, it can be obtained in aqueous solution in sealed ampoules a t a cost of about $35 per millicurie plus service charges. Radium buttons containing about 2.5 microcuries (also as radium bromide) are available as calibration sources for instruments measuring radioactivity. It is strange that the price of radium remains about the same as it was three decades ago, despite the great advances that have been made in the processing of radioactive ores. Scandium and, Yttrium. Though it is not especially rare on the earth, being widely distributed in over 800 mineral species, scandium is one of the most costly and difficult elements to obtain. The metal is sometimes available from chemical specialty houses a t prices ranging from $30-650 per gram depending on the quantity and purity desired. It was found that a number of companies who advertise scandium metal as being available were unable to supply it on demand. The author finally purchased 100 mg for $10. Scandium oxide (99.5-99.9%) is available from several suppliers a t prices ranging from $8.50490 per gram. This provided the largest price range encountered for the same substance with approximately the same degree of purity. Scandium is also represented in the collection by a gram of 99.5% scandium oxide, a white powder. Yttrium of 99+% purity is available from several suppliers a t a cost of about $1 per gram. At least one supplier furnishes ultrapure yttrium. Boron. This elemcnt is available in two forms. For several years electrolytic, amorphous boron (9097%) has been available in quantity commercially in a variety of mesh sizes. Amorphous boron is about $1 per gram; crystalline is about $6 per ounce. The Rare Earths. As has often been said, the rare earths are not earths, nor are they rare. But until recently, because of the great difficulty in separating one from another, many of them in their pure elemental form have indeed been rare. As recently as four years ago lutetium oxide of 96% purity was available only a t prices of about $150 per gram. I n 1954 terbium oxide sold for as much as $500 per gram. However, breakthroughs in ion exchange reactions and other processing techniques have greatly improved the availability and price of these elements. It is now possible to obtain all the rare earths, except for promethium, in elemental form with purity of 99+% a t mod& price. Figure 2 shows samples of all the rare earth metals, except promethium, which is missing from the collection. Typical prices for the metals are as follows: cerium, lanthanum, praseodymium, and neodymium, SO-65C; gadolinium, dysprosium, erbium, and holmium, $11.25; samarium and ytterbium, $1.,50-2.00; thuliumand terbium, $6-7; and lutetium and europium, $13-14 per gram. Eventually it is thought that the more abundant
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rare earth metals may cost from $5-20 per pound; the door is opening toward a much greater use of these elements. Zirconium, Hafnium, Vanadium, Niobium, and Tantalum. Except perhaps for hafnium, these elements are readily available through chemical specialty houses. I n small quantities, the cost of some of these elements has been quoted as follows: niobium, 85,d per gram; 95% vanadium, hafnium, and zirconium, 50.d per gram. Vanadium has been commercially availahle with a purity of 99.5'% a t a price of about $40 per pound. Vacuum, electron-beam melted hafnium is availahle a t about $175 per pound. Tungsten, Molybdenum, Manganese, and Rhenium. Elemental tungsten, molybdenum, and manganese are readily available in large quantities a t moderate cost. Rhenium is more difficult to locate. The author was able to acquire several grams from the Chemistry Department of a Southern university, some rhenium wire from a chemical specialty house, and he was also presented with two pieces of sheet rhenium, about 3 X 1 X 0.001/0.002 in., from a large producer. I n 1928 rhenium cost as much as $10,000 per gram, but small quantities are now availahle in the form of shot, a t a cost of about 82 per gram. Purity is about 99.8%. One company is now supplying rhenium powder of 99.99% purity a t a cost of $580-650 per pound, and rhenium strip of about 0.060-0.001-in. thickness a t a cost of $815-1580 per pound. Gallium and Indiunt. As recently as 1924 it was almost impossible to locate a gram of indium in the United States. Today, 99.99+7& indium is availahle a t a cost of $3-5 per ounce. Gallium, 99.999% pure, is available a t $2-3 per gram. Silver, Gold, and the Platinum Metals. Silver is readily available with a purity of 99.999%. Small quantities of pure gold are available through dental supply houses or suppliers of precious metals. Obtaining the platinum metals is considerably more difficult-not only because of their high cost, but also because of the fabrication charges that are usually added. A troy ounce is usually considered about the minimum order that can be accepted, although suppliers were eventually found who would accept small orders without adding other charges. The price for these metals, excepting platinum (which is available through scientific houses) are as follows: palladium, $2; ruthenium, 84; osmium, iridium, and rhodium $7.50 per gram. The author had hoped to obtain a piece of sheet osmium, thinking that it would make a n interesting piece to exhibit as the heaviest known metal, as reported by some handbooks. He discovered, however, that osmium is difficult or impossible to fabricate and that no supplier could be found. Furthermore, it now appears that we are not sure whether osmium or iridium is the densest metal. Some authorities give a density of 22.57 g/cc for osmium and 22.42 g/cc for iridium. Calculation of the specific gravity of these elements, based on X-ray photographs, has given values of 23.15
for iridium and 22.98 for osmium. Specific gravities as high as 22.8361 have been reported for natural octahe dral crystals of iridium. Figure 3, which shows samples of osmium, iridium, and lithium, includes the heaviest and the lightest metallic elements. Fluorine. Fluorine as a free element is missing from the collection; it is represented by a piece of crystalline fluorite. The most active of all elements, this gas caused injury and death to several of the pioneer investigators. Davy, Gay-Lussac, and Thenard all suffcrcd from the cffccts of inhaling small quantitics of hydrogen fluoride. The Knox brothers, who tried t o study and isolate the element, also suffered from hydrofluoric acid poisoning. I n spite of the fact that liquid fluorine can now be shipped by tank truck in sizable amounts, the author intends to keep his fluorine safely locked up in the form of a beautiful crystal. Astatine, element 85, is also n~issingfrom the collection. Its longest-lived isotope has a half life of only 8.3 hours.
Figure 3.
Heaviest and lightest metollis elements.
The Noble Gases. These are represented in the collection by discharge tubes along with oxygen and nitrogen. The tubes, except for those containing xenon and radon, are available through scientific apparatus houses. The author had a special matching tube containing xenon gas made up a t nominal cost. All the rare gases except radon are available in sealed flasks. I n addition to the discharge tubes, 100 cc of xenon and 250 cc of krypton were purchased for the collection a t a cost of $6 and 7.50 respectively. The excitimg new compound, xenon tetrafluoride, has been offered for sale commercially a t $85 per gram. Thorium gives off a radioactive decay product known as thoron, an isotope of radon, the heaviest of the inert gases. Thoron has a half l i e of 54 sec. Radon-222 has a slightly longer period of 3.85 days. The quantity of radon generated by radium and thorium, while not large, is considered sufficient to let radon be listed as one of the elements of the collection. Thmium, Uranium, Actinium, Polonium, and Prolactinium. The author was fortunate in being able to purchase a very small quantity of thorium and uranium Volume 47, Number 7, July 7 9 6 4
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metals. Depleted uranium, in small quantities, sells for about 50b per gram, and thorium for about $2 per gram. I n large quantities, depleted uranium sells for about $5 per pound, and enriched 235Ufor fuel elements costs about $12 per gram. An AEC permit is usually required for these metals. Actinium has a sufficiently long half life to make it worth while t o add to a collection (28 years for some isotopes), but no source of supply has been found. Polonium in the form of the chloride or nitrate is available commercially a t a cost of about $6 per millicurie plus service charges. An AEC permit is required. The author solved the polonium problem, and gladly so in view of its toxicity, by the purchase of a StaticMaster brush. This contains polonium salts in a carefully sealed compartment under the brush. The maximum body burden for ingested polonium is only 0.03 microcuries, which represents a particle weighing only 6.8 X 10-la g. Weight for weight, i t is about 2.5 X 10" times more toxic than hydrocyanic acid. Protactinium, with a half life of 34,300 years, is also missing from the collection. The bulk of the world's supply is believed to be in the hands of Great Britain's
Atomic Energy Authority. The present cost is about $2800 per Technetium. An AEC permit is required for possession of this element: it is therefore missina from the collection. The cost is presently about $goper gram. Transuranic Elements. The collection contains none of these elements although much interesting data regarding their availability and properties was uncovered. Toxicily and Handling of the Elements in the Collection
The author must admit that several times in the course of preparing the collection he was sorely tempted to give up the project because of the toxicity and dangerous nature of some of the elements. He found the reference work by N. I. Sax, "Dangerous Properties of Industrial Materials" (Reinhold Publishing Corp., New York, 1957) to be very helpful in determining the proper means of handling certain elements. In addition to the radioactive elements, there are some 15-20 others that deserve special attention because of toxic properties. The rare earth metals, scandium, indium, yttrium, and certain others should also be handled carefully because information is still lacking concerning their toxicity.
