SOME SPECTACULAR EXPERIMENTS IN CHEMISTRY
The spectacular experiment is i n frequent demand as a n element in chemistry-club entertainments. Occasionally it may alsofind a legitimate place as a stimulus to waning classroom interest. Other things being equal the writer believes that an element of the spectacular adds to rather than detracts from the value of a demonstration. The following collection i s offered to fellow teachers with the hope that the experiments may prove useful for suck purposes as circumstances and individual good judgment may indicate. The Oxy-Hydrogen Flame First in this series is the spectacular work done with the oxy-hydrogen flame. For best results, i t is advisable to use tanks of the compressed gases instead of trying to run the flame from the ordinary laboratory generating apparatus. These demonstrations are especially impressive when petformed in a darkened room. A.-A rather unusual experiment consists in melting metals in water. For this purpose, the flame is introduced into a large battery jar of water, and by regulating the pressure, it will be found that the flame will continue to burn in the water. While this is going on, one can very successfully melt a wire in the flame. B.-Another very striking demonstration along similar lines is performed by slowly bubbling the oxygen into a large beaker of hot water containing a few small pieces of yellow phosphorus. The phosphorus ignites and brilliantly bums under the water. C.-The atomic hydrogen flame can he easily demonstrated by allowing the oxy-hydrogen flame to pass through an electric arc. D.Synthetic rubies may be made by fusing aluminum hydroxide containing one per cent of chrome alum; for sapphires, titanium oxide is substituted for the alum. In a similar manner, other jewels can be manufactured. The oxy-hydrogen flame can also be used to demonstrate the lime light, the manufacture of glass and alloys, etc. A Safe Method to Explode Large Quantities of Oxygen and Hydrogen For this purpose it will be necessary to obtain a cylindrical cardboard container of one quart capacity. These can be purchased in almost any grocery store. After removing the cap, a longitudinal slit, one-half inch wide, is made in the container, and then a long. piece of cellophane is pasted over the inside of this opening. After thoroughly coating the container with paraffin or shellac, i t is ready for use. I t is filled with water, inverted, and placed upon the shelf of a pneumatic trough of water, and then filled with one-third of oxygen and two-thirds of hydrogen. The 929
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cellophane window serves to indicate the level of the water in the container. When filled with the explosive mixture, the upper rim of the container is grasped with a pair of tongs and then carried to a flame. A tremendous explosion occurs without any of the usual hazards that accompany the use of a bottle. An Experiment to Show That Air Is Combustible This is merely a variation of the well-known reciprocal combustion experiment. The bottom of a wide, cylindrical lamp chimney, clamped vertically to a ringstand, is fitted with a two-hole cork containing an ordinary glass tube and a wide (one-half to one inch) glass tube. The narrow tube extends one-half inch above the cork, while the wide tube extends two inches above the cork. The top of the cylinder is then covered with a sheet of asbestos, containing a one-half inch hole. The illuminating gas enters the chimney through the narrow tube and is ignited above the opening in the asbestos. The gas is adjusted until the flame is about two inches high. The air can then be actually ignited by passing a burning taper up through the wide tube into the chimney. If a wooden splint is now inserted through the wide tube the burning air will ignite it. By then asking the class a question along the following lines, "Why not use air in gas stoves instead of using illuminating gas?" the idea of the experiment can be easily brought out. Spontaneous Combustion The following are six striking demonstrations dealing with spontaneous combustion. Although (B) and (D) have appeared in the JOURNAL OF CHEMICAL EDUCATION previously ( I ) , still they have been included here in order to make the collection more complete. A.-The Apparent Ignition of Alcohol with a Glass Rod. By first dipping a glass rod into a mixture of potassium permanganate and concentrated sulfuric acid, and then touching the wick of an alcohol lamp with it, the alcohol will ignite. B.-Igniting Wood with Sodium Peroxide and Water. For this purpose, a mixture of sodium peroxide and sawdust is placed in a pan in the sink. If a small amount of water is then dropped upon the mixture an intense combustion takes place, emitting a blinding yellow flame. C.-The Apparent Burning of Water. A small piece of sodium or potassium is put into a beaker. If water, containing a small amount of ether, is then poured into the beaker, the ether ignites, giving the illusion that the water is burning. D.-Pouring Red Hot Lead from a Cold Test Tube. A good pyrophoric powder is easily made by heating lead tartrate in a hard glass test
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tube until no more fumes are evolved. The tube is then tightly corked and allowed to cool. When sprinkled into the air, the colloidal particles of lead and carbon take fire spontaneously, creating the illusion that the cold test tube actually contains red hot lead. The effect may be increased by pouring the mixture on gunpowder. E.-Spontaneous Combustion of Acetylene in Chlorine. If the delivery tube of an acetylene generator is held in a bottle of chlorine, the acetylene ignites spontaneously. F.-A Safe Way to Prepare Phosphine. A two-ounce wide-mouth bottle is fitted with a two-hole rubber stopper containing a delivery tube and a wide tube (one-half inch diameter). The delivery tube is flush with the bottom of the stopper. The wide tube extends to within one inch of the bottom of the bottle, and also extends one inch above the stopper. The delivery tube leads into a pan of water from which i t should not be removed until the evolution of the phosphine has stopped. The generator is then filled to within one-half inch of the top with hot water. Small pieces of calcium phosphide are now dropped in through the wide tube, and then the tube is corked. A steady stream of phosphine is thus safely generated, resulting in the formation of the characteristic smoke rings as the gas leaves the pan of water. At the end of the demonstration, the cork is removed from the wide tube and then the tube is connected by rubber tubing t o the cold water faucet. By gradually turning on the water, the reaction mixture is washed out of the bottle.
A Simple but Effective Way to Show the Increase in Weight upon Heating Metals in Air A large bundle of iron wool is counterbalanced on a beam balance. It is then held, by means of tongs, above a small flame until it ignites. The wool is then removed from the flame until i t stops sparking. The entire process is repeated until all the iron has completely burned. Upon reweighing, the increase in weight is very apparent. One must be careful not to burn the wool too rapidly so as not t o lose too much of the iron in the form of sparks. Fusible Alloys The four components of Wood's alloy are heated separately in four test tubes of water. It will be found, of course, that none of the constituents melts in the hot water. The water is then poured out, and the four metals are fused together in a crucible. The molten mixture is then poured on the stone table-top so as to form a long, thick strip. A piece of the strip is then heated in a test tube of water into which a thermometer bas been ' inserted. It will be found that the metal strip melts around 60%
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Kindling Temperature
A burning match is inserted in a test tube full of kerosene. The flame goes out and thus the question of kindling temperature is brought up. Some kerosene is then ignited in a casserole and poured from a height of about three feet through a large, wire gauze held above a battery jar. The wire gauze effectively extinguishes the burning stream of kerosene, which thus serves as an interesting approach to the study of the miner's safety lamp. Fire Extinguishers A.-Pyrene. Two 500 cc. beakers are each filled with 50 cc. of kerosene. Both are ignited. Water is then slowly added to one of the beakers. It will be found that the water is ineffectual in extinguishing the burning kerosene, because the oil floats to the top. One-third of a test tube of carbon tetrachloride is then added to the second beaker of burning kerosene. The flame is extinguished a t once, amid a puff of black smoke. The commercial application-Pyrene-is then exhibited. B.-The Chemical Fire Extinguisher. The top of the chemical fire extinguisher is unscrewed and the bottle of sulfuric acid is removed. Some of the sodium bicarbonate solution is then withdrawn from the tank and a small amount of the sulfuric acid is added in order to show the action involved. A miniature fire extinguisher is then assembled and used for extinguishing some burning paper in a pan. C.-Foamite-Firefoam. One-half inch of kerosene is put into a trough and ignited. When the kerosene is burning strongly, the instructor calmly pours both Foamite solutions into the trough from opposite sides. The flames are extinguished almost immediately by the thick foam formed by the reaction. Solution No. 1 contains sodium bicarbonate; solution No. 2 contains alum and licorice. How to Obtain a Positive Test for Ammonia during Destructive Distillation The addition of lime to the coal-tar collector insures the test for ammonia (2). Preparation of Liquid Ammonia and Ice During the laboratory preparation of ammonia, the delivery tube is placed in a test tube standing in a wide-mouth bottle of "dry ice." The manufacture of ordinary ice is then easily illustrated by standing a small test tube of water in the test tube of liquid ammonia. If so desired the liquid ammonia may first be used to cool brine, which in turn will freeze a smaller test tube of water. In the same way, other gases may be liquefied.
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Thermite The well-known experiment on thermite can always be depended upon to arouse an intense enthusiasm for science. For this demonstration, i t is first necessary to prepare a plaster of Paris cone. This is made by coating the inside of a large funnel with vaseline. A large paper cone is placed inside, and it also is coated with vaseline. A hollow plaster of Paris cone is now made, using the prepared funnel as a mold. Before the plaster sets, a hole is made in the bottom of the cone. When the plaster is hard, it can be very easily slipped from the funnel. The cone is placed in a large ring on a ringstand, a t the base of which is a pan of sand. A piece of paper is stuffed into the opening a t the bottom of the cone so as to prevent the ignition mixture from dropping out. The cone is then filled with the mixture of aluminum powder and iron oxide. Other oxides, of course, may be substituted. To insure a good yield of molten metal, a liberal number of iron brads is added to the mixture. On top of the mixture a very small heap of an oxidizing agent is placed. A piece of magnesium ribbon is then stuck into the oxidizer, the cone is covered with a sheet of asbestos, containing a small hole for the magnesium strip, and the magnesium ribbon is ignited. This demonstration is most dazzling and impressive when shown in a darkened room. Chromium Plating Prepare some red chromium trioxide by adding concentrated sulfuric acid to potassium dichromate. Filter through glass wool and dissolve 300 g. of the trioxide in one liter of water containing 5 cc. of concentrated sulfuric acid. Clean the object to be plated and hang it on the cathode. A lead plate is used as the anode. The cell is then covered with a sheet of paper to prevent fuming. It is advisable to use a heavy current density (10-20 amp.) and also to keep the solution a t a temperature of 50°C. For the best results i t is well first to plate the object with nickel. Colloids An impressive experiment on colloids is performed in the following manner. A carbon arc is struck in a beaker of water. It will be found that the arc is much more brilliant in the water than it was in the air, due, perhaps, to the absorption of the red heat waves by the water. After the arc has been running for about ten minutes, some of the water is put into a small crystallizing dish. The dish is then placed upon the stage of a microscope and the lens is immersed in the water. By sending a strong
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horizontal beam of light through the water, the characteristic, scintillating opalescence of the Brownian movement shows up extremely well. The Claude Process for Obtaining Power from Warm Sea Water By making several slight modifications in the standard distilling apparatus, the Claude process can very easily he demonstrated. A small, efficient turbine is connected between the distilling flask and the water condenser, and the distillation is conducted under vacuum. In order to duplicate actual conditions as far as possible, the water is first heated to 70°F. This represents the warm water a t the surface of the sea, while the cold water in the condenser corresponds to the low temperature water obtained from the depths of the sea.
A Model Electric Lamp A model electric lamp can he easily made in the following manner: A th'm wire, the filament, is attached to two copper lead-ins, held in place in a Florence flask by means of a one-hole rubber stopper containing a glass tube. The glass tube is then connected to an exhaust pump and the two copper leads, a t the sides of the stopper, are connected to the lighting circuit. A rheostat must he used in order to regulate the current so as to prevent blowing out the makeshift filament. As the air is gradually exhausted, i t will be found that the filament becomes brighter and that tungsten is the only material that emits a bright light without burning out. An Experiment on the Radiation and Absorption of Heat For this demonstration it will be necessary to silver an air thermometer bulh. This is easily done by warming the bulh and then placing the tube in a beaker of the silvering solution. As the glass cools the silvering solution is drawn up into the hulb. Heat the bulb to silver it and then drive the spent solution out by reheating it. A second air thermometer bulb is then blackened by heating it in a luminous flame. Each is then clamped to a separate ringstand, bulhs upright, the open tubes resting in two separate beakers of colored water. The two indexes are then adjusted to the same level. If a luminous flame is placed midway between both bulbs, the indexes will indicate that the blackened bulb absorbs more heat than the silvered hulb. A Simple Photoelectric Cell Although the following cell is very easy to construct, still it is extremely sensitive to light (3).
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This device, a type of voltaic cell, generates current continuously, but under the influence of light, however, its output jumps up several milliamperes. The cell, which can be set up in a beaker, uses a solution of lead nitrate as the electrolyte, a lead plate as the cathode, and a copper plate, coated with cuprous oxide, as the anode. The anode is easily prepared by gently baking a clean copper plate for about one-half hour. If the temperature is carefully regulated, the plate will become coated with a thin layer of red copper oxide. A high temperature should not be used as it forms the black oxide. Under the influence of light, the cuprous oxide loses electrons and changes to cupric oxide, thus increasing the output of the cell.
Literature Cited (I) JORDY,"Explosives; a Burlesque Lecture," J. C ~ E M Eouc., . 7,653 (Mar., 1930). (2) FLETCHER AND FINE, "Destructive Distillation," ibid., 8, 151 (Jan., 1931). (3) BAYER, "Light-Sensitive Cells." Radio News, April, 1929.
