Three Magic Metals (Jun, 1936)
Three Magic Metals
Producing Cold With Electricity and A “Quicksilver Heart” That Beats Are Only Two of the Amazing Tests You Can Perform Easily With Simple Substances
By Raymond B. Wailes
YOU are accustomed to seeing an electric element in a toaster or radiant heater grow red-hot when current passes through itâ€”but did you know that when electricity flows through joints of certain metals, it produces a cooling effect? Have you ever made a drop of murcury behave as if it were alive or prepared a pair of magical alloys that are solids when separate, and a liquid when mixed?
These are a few of the fascinating experiments that you can perform with metals, using three in particular that you may not have employed before in your home laboratoryâ€”mercury, antimony, and bismuth.
You may already have discovered that many of the metals needed in your experiments can be found in your home. They should be prized, bottled, and labeled like any other chemicals. The shell of an old dry cell will furnish you with zinc, and worn-out pots and pans with aluminum while the mesh scrapers used to clean them supply copper in handy form. Likewise, mercury, which is expensive to buy, may be available right at hand. It can be salvaged from a broken or discarded thermometer, provided, of course, the instrument is not one of the kind that uses alcohol colored with a dye. The quantity of mercury will be small, but it will be ample for a number of tests, and it is easy to clean and use over and over again.
Only a drop of the liquid metal is required for a striking demonstration known as the “mercury-heart” experiment. Place the mercury in a small, shallow vesselâ€” a glass caster well from the ten-cent store
will do nicelyâ€”and cover the drop with a dilute solution of sulphuric acid. One part of strong acid to six parts of water makes a suitable solution, which should be colored faintly purple by the addition of a drop of potassium permanganate solution.
Now thrust a sewing needle into the solution from the side, jabbing the point into the drop of mercury, and you will receive a surprise. The drop will hump itself up, as if alive, and retreat from the needle. No sooner has it done so, however, than it flattens out again, repeating the pulsation each time it comes in contact with the needle point.
The same materials will serve for a “tidal-wave” experiment. Only enough of the colored acid should be used, this time, to encircle the drop of mercury, leaving its upper sur-face uncovered. Hold the needle vertically and touch it to the surface of the mercury drop. Then draw the needle sideways until it just meets the solution. Immediately the mercury gathers itself up about the needle, while the solution backs away. The mercury then relaxes and flattens out as before. The pulsation will continue for a considerable time. Changes in the surface tension of the mercury, caused by the electrical action of the metals and the acid, account for the remarkable behavior of the drop of metal in these two experiments. Alloys of mercury with other metals are called amalgams and one of the most curious of these is a double amalgam known as Mackenzie’s alloy. To make it, grind together in a mortar one part of mercury and two parts of bismuth metal, by weight, until a homogenous product is obtained. This is a bismuth amalgam. Make a lead amalgam in the same way, using three parts of mercury and four parts of lead, again measured by weight. The bismuth amalgam and the lead amalgam are both solids at ordinary temperatures. Place some of each in your palm and rub them together. Presto! They are transformed into a liquid alloy that you can pour freely from hand to hand.
An amalgam of magnesium metal and mercury may be made by rubbing the two together in a mortar with a pestle. Considerable heat is liberated as the metals unite, if the magnesium is in powdered form. The magnesium alloy that results is notable for its ability to decompose water, releasing hydrogen gas. Heating the water will make the effect more marked. The magnesium interacts with the water to form magnesium hydroxide per oxide, while the mercury can usually be reclaimed at the end of the experiment.
A few hints on working with mercury in the laboratory will not be amiss. Because of its propensity for forming amalgams with other metals, a wise precaution is to remove any valuable rings from the fingers before handling it. Gold and silver, by contact with mercury, quickly acquire a silvery coating of amalgam. If a piece of jewelry is made entirely of gold, however, and contains no stone or part that might be damaged by heat, the mercury may be volatilized and driven off by heating the article gently.
Spilled mercury is elusive, but may be picked up with a thin scoop of stiff paper, if the drop is first wetted. Mercury can be cleaned by filtering it through chamois skin, applying pressure with the fingers if the quantity is small. Shaking mercury with weak nitric acid (about an eight-percent solution) is another way of purifying it. This tends to dissolve any foreign metals that may be present as impurities. Two of the most interesting metals for home experiments are antimony and bismuthâ€”a pair so alike in their properties that they might be called chemical brothers. You might search your house high and low without finding either of these elements for they appear in everyday life only in the form of a few compounds. Ask for bismuth at a drug store, for example, and you are likely to get the subnitrate or subcarbonate, which are used medicinally for certain stomach disorders. Antimony is contained in potassium antimony tartrate, more familiarly known as tartar emetic. The most striking experiments require the metals themselves, however, and these may be obtained from dealers in chemicals, usually in the form of lumps and powder mixed.
By passing an electric current through a couple or junction of antimony and bismuth, you can produce either a heating or a cooling effect at will. This strange phenomenon is known as the Peltier effect, after the French scientist who discovered it in 1834. To demonstrate it, you will need a fair-size lump of each metal. The pieces should be attached with bare copper wire to a pair of long, metal knitting needles passing through the cork of a flask or bottle and serving as supports. Adjust them so that the lumps of antimony and bismuth are in contact with each other. If the lumps available are not large enough, you can form pieces of the desired size by melting the powdered metals and casting them in a paper mold. Pass a glass tube through a third hole in the cork and place the flask tightly on the cork. The apparatus should be arranged so that the glass tube dips into a beaker or small wine glass filled with colored water. The whole arrangement will act as a thermometer.
Now connect two or three dry cells, as shown in the diagram, and attach wires from them to the knitting needles, thus closing the circuit and setting up a flow of electric current through the antimony-bismuth couple you have made. When the direction of the current is from the antimony to the bismuth, the couple will be heated, the air in the flask will expand, and you will see bubbles of air emitted from the tube that dips into the beaker. But if the current is made to flow in the opposite direction, the junction of the metals is chilled, and the air in the flask contracts, as evidenced by the water rising in the tube. You are observing a remarkable phenomenon, direct cooling by an electric current which, if it could be applied practically to a device like an electric refrigerator, would eliminate all moving parts and produce a silent, efficient apparatus that would never wear out!
Once brought to its ignition point, metallic antimony burns in the air almost as readily as paper. You can show this by heating a pellet of antimony upon a charcoal block until it begins to burn, and then tossing it upon the inverted lid of a paper box. Rolling and bouncing from side to side, it continues to burn in the air as the coating of oxide that would smother it is continually knocked off. Its temperature becomes high enough to scorch the paper of the box lid, leaving tracks that record the movement of the large globule and the smaller ones that break off from it. If the antimony is simply melted and dropped upon the box lid, it will smolder for about a minute, emitting white smoke and leaving a trail of the oxide behind it. White fumes of the oxide are also produced if antimony is heated upon a charcoal block with a pointed flame, such as that of a blow-pipe. Finely powdered antimony or bismuth burns rapidly if it is thrown into a Bunsen flame, and a pinch of antimony tossed upon molten potassium nitrate that you have heated in a tin-can lid or a crucible takes fire with a shower of sparks.
Antimony and bismuth, like iron, decompose water when heated red-hot. They react chemically when heated with sulphur or when dropped into a vessel of chlorine gas, producing heat and sometimes light. Sulphides and chlorides of the metals are formed as a result.
When you try to dissolve antimony chloride or bismuth chloride in water, you will notice that a white precipitate is always produced unless a drop or two of hydrochloric acid is also added. The acid dissolves the white precipitate, which is a basic salt of the metal being used and is known as an oxychloride. Nearly all antimony and bismuth chemicals produce precipitates of this kind unless enough acid is present to keep the oxychloride in solution.
YOU can apply this fact in an effective little chemical trick. Make a solution of the chloride or nitrate of either antimony or bismuth, using just enough acid to give a clear, waterlike liquid. Hold half a glassful of this solution under a faucet, and add enough water to fill the glass. The contents change from “water” to “milk” as the white precipitate of oxychloride appears, due to the reduced concentration of acid. To one who is not in on the secret, it looks as if you drew a glass of milk from the water faucet.
A peculiarity of bismuth oxychloride is that it is somewhat photosensitive, turning gray in sunlight. A chemical difference between the oxychlorides of antimony and bismuth can also be shown. Adding a few crystals of tartaric acid will cause a precipitate of antimony oxychloride to redissolve, while a precipitate of bismuth oxychloride is unaffected. This may be used as a test to distinguish between antimony and bismuth.
Place a strip of iron or zinc in a solution of an antimony or bismuth salt, to which a little acid has been added to prevent formation of the oxychloride, and metallic antimony or bismuth will be deposited upon the foreign metal. A strip of copper placed in a solution of antimony chloride, which has been acidified with strong hydrochloric acid, becomes covered with a curious violet-colored mass. This is known as Reinsch’s test for antimony.
Antimony may also be detected by a method closely resembling Marsh’s test for arsenic, described in an earlier issue (P.S.M., Dec. ’34, p. 56). Hydrogen gas, generated in a flask from zinc and sulphuric acid, is led through a drying tube containing anhydrous calcium chloride and then through a horizontal piece of glass tubing about eight inches long, which is gently heated with a small flame during the experiment. After hydrogen has been generated for five or ten minutes to clear the apparatus of air, admit the solution to be tested for antimony to the generating flask, through a thistle tube or a separatory funnel.
ANY antimony that is present in the chemical will combine with a part of the hydrogen, forming a gaseous compound of antimony and hydrogen called stibine. When the stibine gas reaches the heated outlet tube, it will be decomposed, and a metallic mirror of antimony will be deposited upon the inner surface of the glass. If the gas issuing from the outlet tube is ignited, a cold porcelain dish held in its path will also receive a deposit of antimony. The zinc used in this experiment, if not of high purity, may contain some arsenic, and this will produce a deposit of similar appearance. The two are readily distinguished, however, by a simple test. The antimony stain will not dissolve in a solution of bleaching powder, while the arsenic deposit will. Try the test first upon a compound that you know contains antimony, for practice. If the gases are not being burned at the end of the outlet tube, the room should be kept well ventilated while you are performing this experiment.
Stibine, formed in the test just described by the combination of antimony and hydrogen, is known as a hydride. The gas has been detected issuing from storage batteries while they are being charged, as a result of the combination of hydrogen liberated during the charging process with antimony present in the lead plates of the batteries.
Melt some bismuth in a crucible, and you can obtain a sample of the crystals produced by this metal. Let the molten bismuth cool until a hard crust forms on the surface. Then break the crust with an iron rod and pour out the remaining liquid. The crystals will be found adhering to and covering the inside walls of the crucible.
Antimony and bismuth form a variety of peculiar and interesting alloys with other metals. One, containing antimony and copper, has a beautiful purple color! Another, consisting of bismuth, tin, and lead, will enable you to “silver” the inside of a flask or a bulb blown from glass tubing.
MELT four parts of lead, by weight, in a crucible; then add six parts of tin. When all is molten, stir in ten parts of bismuth. A piece of glassware in which the resulting alloy is placed, gently heated, and swirled about, will receive a silvery inner coating and will make an interesting exhibit to add to your chemical museum.
Though their names may be unfamiliar to the layman, antimony and bismuth have a number of commercial uses. Type metal is made of about seventy-five parts of lead, twenty of antimony, and five of tin; unlike most substances, it expands upon solidifying, thus giving a clear impression of the type mold. Babbitt metal and Britannia metal are other alloys containing antimony. Bismuth alloys, which melt at remarkably low temperatures, are employed in automatic sprinkler systems for fire-fighting. Salts of bismuth are employed medically, as already noted, and are also used in the manufacture of hand lotions, cosmetics, artificial pearls, porcelain enamels, and certain paints.