Demons in Demonstrations' ELBERT C . WEAVER Phillips Academy, Andover, Massachusetts
T
HE demons in demonstrations are five malevolent monsters: money, minutes, mystery, monotony, and
muss.
The money monster can never be muzzled completely, but he can be kept in check. Whenever practical we can order chemicals in large lots, and apparatus in case lots. Also, we can check the grade of chemicals to be sure that the quality specified in our order is not too good for the purpose for which the substance is to be used. For example, commercial (technical) quality copper sulfate contains some ferrous sulfate, but this grade of the compound is perfectly satisfactory for introductory electroplating and replacement experiments. For quantitative determinations of the percentage of moisture in the hydrated crystals, however, we find that a better quality with small crystal size is desirable. Recoverable residues and by-products may be saved from some experiments. We know that in such cases the labor cost of the recovery of a small quantity far exceeds the money value of the product. If, however, the instructor selects the right pupil and suggests that crystals can be coaxed from an unlikely-looking mass of material, the results may be valuable in terms of education. A satisfactory method of dispensing solids to pupils in the laboratory consists of the following procedure: Two-inch squares of used paper are cut,,and the proper amount of solid reagent is placed on the paper by the instructor or assistant, one paper for each member of the class. This eliminates waste and the messy effect so often noticed around the supply shelf. For dispensing small quantities of liquid reagents, several glass tubes are put into an open jar of the liquid. The pupil covers the top of the tube with his thumb or finger and transfers the proper small amount of liquid within the tube to a test tube. For volatile liquids, the glass tube is inserted through a stopper of the jar or bottle, the same dispensing technique that is used in semimicro work.
The first demon of this exhibit is an S-shaped creature with a green back. He has two broad stripes down his back, a coppery tail, and a silvery head. He is a constant annoyance, but he becomes especially obstinate once or twice a year. The most frequent habitat of this demon is the offices of school superintendents, principals, and purchasing agents. He is the demon known to us all-the expense demon, money. In most cases we have a limited or a shriveled budget for supplies. The cost per pupil for apparatus and supplies in science courses brings many a raised eyebrow in the purchasing department. T h e published catalogs of scientific supply houses disappoint the bar: gain hunter, and somehow the most desirable pieces of apparatus and the most interesting chemicals seem to have an almost prohibitive price tag. A few methods of subduing the expense demon are suggested. We all use glass jars and containers for gascollecting bottles, generators, and for holding specimens. Today many foods come packed in glass jars which have wide mouths and are the size needed for collecting gases. Pupils will supply these jars from their homes if requested, for usually they are thrown. away after use. For cover plates, cut squares from pieces of scrap window glass. Trimmings can be obtained from a local pidnre-framer or glazier to serve this purpose. Labels can be made inexpensively from a sheet or a roll of gummed paper, and a protective varnish coating can be made by dissolving old toothbrush handles in acetone. Some chemical supplies can be obtained a t local stores a t reasonable prices, and the "red tape" of a formal order in triplicate with priority statements attached may be Tl -avoided, perhaps. Chemicals that sometimes may be pompous^ and verbose The second demon is a purchased locally to advantage include Epsom salts, lye, common salt, Glauber's salt, blue vitriol, triso- creature. He bas the habit of changing his attention dium phosphate, bicarbonate of soda, washing soda, from one subject to another. His procrastination is borax, cream of tartar, saltpeter, tincture of iodine, famous. He is called lack of time, .or the minutes , - - ~auu -..A . . . . w . . . .u ~ . monster. He comes out of his haunt and prowls when sugd~"1c irdu, x u the principal extends himself at schooi assemblies, An audience-participating demonstration given at the Sixth whed poli&al rallies, athletic events, quasi-patriotic Summer conference of the New England Association of Chunisand performances try Teachers, Connecticut College, New London, Connecticut, meetings, air-raid interfere with the time regularly allotted to classroom August 25, 1914.
Tom Sawyer in whitewashing the fence in Mark Twain's famous story while the pupils learn by actual performance. IV
Beware of the monotny monster, especially on the day before a rainstorm. The author of a well-known texhook sent these suggestions: "The teacher has to be something of a born actor and enter into the experiment with the pupil's enthusiasm, forgetting for the moment that he has done the experiment many times. Often the teacher rushes through the experiment and doesn't stress the points illustrated. Also he fails to call on the class to assist in the demonstration and the pupils take little interest in it. Scatter the demonstrations along as they come in 'pat.' Pupils soon forget what we tell them, but they often remember what they do or see us do, especially if the experiment didn't go as expected. But experimental failures must not happen often or the class loses interest in chemistry or its confidence in the teacher's ability." Various means are available to avoid monotony. Among them are the injection of humor, a change of pace, a change of voice, the use of color in both experiments and blackboard crayon, changing'the temperature of the room, and, most important of all, an attitude of contagious enthusiasm on the part of the demonstrator. Examples of advantageous application of color in blackboard diagrams include the Sicilian and the Frasch methods of obtaining sulfur, Lavoisier's classic experiment in which he proved the part played by the air in ordinary burning, Priestley's preparation of oxygen from mercuric oxide, and equations for the formation of colored precipitates such as antimony sulfide, arsenic sulfide, and silver chromate. Actually plunge a red-hot silica or Vycor crucible into cold water and find out what happens. A green-edged flame about two feet high from a flask containing boilmg alcohol, sulfuric acid, and borax is an arresting sight, demonstrating the test for the borate radical. Quotations read from original sources are helpful to vary the classroom program. But among all these means, the greatest aid to overcome monotony is pupil participation. v The demon muss is a mocking monster. When the dismissal bell rings and the teachers beat the pupils in the race for the schoolroom door in the rush to get the big wages at the defense factories, then the chemistry teacher is left alone to prao~le .. with the monster, muss. Not only must chemistry apparatus be taken out, assembled, and set up, but i t must also be washed, cleaned, and put back into the storeroom. In this respect, chemistry demonstrattng is unique, in fact, uniquely unpleasant. Some of the most enlightening experiments make quite a little muss, and they spatter, especially if they get out of control. The thermit reaction is well worth the trouble it takes
-
to demonstrate, even if sometimes a crucible cracks and molten steel and slag coming through mar the top of the lecture desk. Even the simplest reaction of double replacement calls for the use of a t least one vessel which must be cleaned afterwards. But the billowy garnet clouds of silver chromate, or the brilliant yellow dense precipitate of lead chromate are well worth all the muss they make. Demonstrating relative vapor pressure calls for careful adjustment and construction of manometers. Three equivalent bell jars have rubber stoppers a t the top through which a manometer partially filled with colored water projects. The bell jars are placed over evaporating dishes containing, respectively, equal quantities of water, alcohol, and ether at the same temperature. For demonstrating equilibrium, a large vessel is required. Bismuth trichloride is placed in water and stirred. The reaction
is made to go either way by the addition of water or by the addition of hydrochloric acid. The settling of muddy water by a floc of ferric hydroxide or aluminum hydroxide needs a large vessel and a lot of material for a really effective demonstration. This is very mussy to clean. Tops in muss is the demonstration of fire foam. A dish of burning gasoline is shown to be unextinguishable by pouring in water. Then a mixture of sodium bicarbonate and licorice powder in water is stirred with concentrated aluminum sulfate solution. The resulting suds is allowed to roll over the edge of the beakers holding the solutions onto the gasoline fire, but often i t doesn't stop a t the edge of the dish containing the burning gasolbe. Like "ole man river," it just keeps rolling along. Coagulating warm milk by acetic acid leaves a grabaceous residue, and the many Dry Ice experiments can result in considerable muss. These experiments are well worth the discomfort of cleaning up. Here, then, is a demon which must he endured, but he can be subdued by skill and industry. Following is a list of references on lecture demonstrating in chemistry. REFERENCES BENEDICT,F. G., "Chemical Lecture Experiments," Macmillan Company, New York, 1901. VANKLOOSTEK, H. S., "Lecture and Laboratory Experiments in Phvsical Chemistry." .. Chmical Publishinn- C o m.~ a n ..v .Easton. pa:, 1925. DAYISON,H. F., "A Collection of Chemical Lecture Experiments," Chemical Catalog Company, New York, 1926. NEWTH.G. S.. "Chemistrv Lecture Exoeriments." Lonmans. and ~ b m p a n y~, e York, & 1922. ' FOWLES, G., "Lecture Experiments in Chemistry," The Blakiston Company. Philadelphia, 1939. ARTHUR,P., "Lecture Demonstrations iu General Chemistry," AkGraw-Hill Book Company. Inc., New t o r k , 1939. E ~ o m A. , L., "Demonstrations and Experiments in General Chemistry," Harper and Brothers, S c w York, 1937.
ree en
