SOME PROJECTS IN CHEMISTRY
Chemistry, like physics, is essentially a laboratory science. Most of what we know about either subject has been learned by careful experimentation, close observation, and thoughtful reasoning about the observed results. I t would appear that a similar procedure should be an acceptable method for the beginner. Nobody, of course, expects the neophyte to rediscover Avogadro's Principle, the Law of Gay-Lussac, or the rate of diiusion of gases, but there is much knowledge which be might uncover for himself under suitable conditions. Our textbooks in chemistry give in considerable detail the properties of the common elements and their chief compounds. The student who goes to the laboratory to prepare one of these substances knows in advance what results he should obtain. He knows that the carbon dioxide he is presently to prepare will be colorless, odorless, will not bum, and will turn lime water milky. He knows that the ammonia gas about to be made will be colorless, extremely soluble in water, and will not support combustion. It seems a pity that our textbook writers should thus, by telling the student everything which he might find out for himself, destroy that joy of discovery which otherwise might be his. Knowing, as he does, what results are to be obtained in almost any of the ordinary experiments, the student sinks from the r81e of a discov&er into that of a verifier and under such conditions laboratory work may become more or less a perfunctory performance deriving much of its value from the acquisition of certain manipulative skills. With the thought of providing some experimental work in which the results of experiment would not be known in advance, certain projects were devised for use in our chemistry classes. In casting about for material, several propositions were considered. At last we decided upon the projects involving the conversion of crude materials into finished products. What can be more interesting for the student of chemistry than to start with a sample of some ore, say witherite, and proceeding under direction finally produce the beautifully white crystalline product, barium chloride? There are many such projects which are within the ability of the student and which provide an avenue of escape from the usual procedure of the laboratory. There is also the added incentive of preserving samples of the original and the finished product; these samples are tangible substances of distinct color or crystalline form quite different from the monotonous similarity which a series of samples of the ordinary gases would have. Recently we gave one of our students some magnesite to be worked up into Epsom salt. The ore was crushed in an iron mortar and the 1656
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powder was slowly added t o fifty cubic centimeters of dilute sulfuric acid with constant stirring until effervescence ceased. The sirupy product was heated with addition of a little more of the powdered ore until i t was evident that the acid had been completely converted into the salt. Water was then added, the liquid was well stirred and filtered into a clean crystallizing dish. The dish was set aside and after some days when most of the liquid had evaporated, crystals of the salt were seen in abundance. The mother liquor was drained off, the crystals were dissolved again in as little hot water as possible, the liquid filtered and recrystallized. Glassy crystals of the salt were produced. These were filtered off, dried on hlotting paper, and a sample put up. A specimen of the anhydrous salt was obtained by gently heating the crystals. The student may now write a little book telling the story of how his product was obtained and this, with his various samples, can he made into an attractive poster. Such work as this enlists a t once the interest and effort of the student. Another student, starting with malachite ore, produced specimens of copper and the chief copper salts. Another one produced antimony chloride solution from stihnite. The ore was powdered and treated under the hood with concentrated hydrochloric acid until no further evidence of hydrogen sulfide was noted. Too large an excess of the acid was avoided. The product was then filtered and you should have seen the student's eyes open when he let a drop of the liquid fall into a graduate full of cold water. If interest is a thing t o he desired certainly nothing we have ever tried has given us more satisfaction in the interest evoked and the effort put forth in this kind of work. Another project was: What shall we do with the marble dust that we find in considerable quantity in the calcium carbonate we buy? The dust was sifted out, treated with dilute hydrochloric acid till nearly dissolved, the liquid heated to expel carbon dioxide, and then evaporated to dryness t o expel any excess of acid. The residue was taken up with water and any iron present precipitated by cautious addition of ammonium hydroxide. The iron hydroxide was filtered off, and the filtrate evaporated to dryness, using a small flame along toward the end and keeping the material well stirred. A lumpy white product was thus obtained which answers well enough for our use as calcium chloride. We use specimens of this preparation to show the rapid absorption of ammonia gas over mercury and always state that the material used was prepared by student So-and-so. Teachers who may desire occasional experimental material somewhat different from that of the usual laboratory manual may do well to undertake some work of the kind outlined above, Our experience has been that students will respond eagerly to an occasional proposition like this: "We are running low on barium chloride, Jack. Would you like to make
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one hundred grams of it for us?" There are few students, I think, who would not jump a t such a chance. When a student has completed a project of this kind, say the preparation of one hundred grams of lead nitrate from litharge or cerussite, he finds much satisfaction in seeing his product put into a bottle on a shelf in the laboratory for general use and labeled "Made by . . . . . . . . . . . . . . ." That his product is not chemically pure is true but i t is good enough for general use. It may be argued that this is advanced work which ought not to be taken up until the pupil has finished the usual course in general chemistry. In reply, we may ask: "In what way is this advanced work? Are the processes of solution, filtration, evaporation, and crystallization any different than they are in the preparation of the usual substances? Are the chemical equations for the reactions involved any more complicated than are those of our customary experiments? Is the reaction between lead oxide and nitric acid as difficult to understand as is that between copper and nitric acid? Is the decomposition of copper carbonate in the preparation of copper oxide any more difficult to comprehend than is that for the decomposition of potassium chlorate? Should you think that the pupil who understands the reaction between calcium carbonate and hydrochloric acid ought to have any difficulty in understanding the reaction between cerussite and nitric acid?" It does not seem so. Obviously experiments of the type described above ought not to displace those which are required in the usual course. But wherever opportunity of time and ability on the part of the individual student seems to warrant, work of this type may be undertaken with the assurance that there will develop a new interest and enthusiasm not equaled by that shown toward the ordinary preparational work.
