VOL.4, NO. 12
QUALITATNB ORGANIC ANALYSIS
1529
QUALITATIVE ORGANIC ANALYSIS IN THE ELEMENTARY ORGANIC COURSE A.
T.BAWDEN, BAYLORCOLLEGE, BELTON, TEXAS
In teaching general chemistry, qualitative analysis is rather generally used only as a means of reviewing principles already studied and in training the student in careful manipulation. A few teachers recognize in qualitative analysis a method of teaching general chemistry. Qualitative analysis can be made to aid materially in organizing and storing up the facts of general chemistry, and nothing better can be found to teach the physical principles included in the usual general chemistry text. Several authors of qualitative analysis texts have shown that it can also be used to teach the fundamentai principles of quantitative analysis. Qualitative analysis is exceedingly valuable in that it interests the students. A few teachers have considered qualitative analysis to be so valuable as a teaching tool that they have the students gradually build up their own schemes of analysis, rather than furnish them with a finished scheme. Since inorganic qualitative analysis is not taught for its own sake, but is employed as an aid in teaching general chemistry, why should not organic qualitative analysis be used as a tool in teaching organic chemistry? Among all of the courses in inorganic chemistry, general chemistry has had the blackest name among the students. There is probably no subject which requires more teaching ability, with thepossibleexceptionof pandemic chemistry. In the organic field there is no course that has such a black name, as the first course. In our meagre experience there is no course in chemistry which is more sinned against. Methods of teaching organic chemistry have not been developed by the majority of teachers. The purpose of the laboratory work in organic chemistry may be stated as follows:
1. To give a first-hand study of the preparation and properties of typical organic compounds. 2. To make the relation between classes, and members of classes of organic compounds more real. 3. To give the student knowledge and skill in the fundamental operations carried out in the organic laboratory. Qualitative analysis will do all that the usual seed-catalog type of laboratory manual does in giving the student first-hand knowledge of organic compounds. The usual course in organic chemistry takes up fist the separation and purification of organic compounds, studying such operations as solution. filtration, the use of immiscible solvents, crystallization, sublimation,
fractional distillation, steam distillation, tests of purity and determination of melting and boiling points. A course in organic qualitative analysis must necessarily cover these same items in the first few laboratory periods. The usual course then spends some time on qualitative organic analysis studying the detection of organic substances, of C, H, N, and the halogens, but seldom relates this work to any that follows. So far our two courses are identical. By the proper selection of from ten to fifteen unknowns from the preparations generally studied in the laboratory in aliphatic chemistry such as hydrocarbons, halogen substitution products, alcohols, ethereal salts, ethers, aldehydes, ketones, acids, esters, carbohydrates, and nitrogen derivatives, we find that most of the substances generally prepared in the laboratory are actually prepared as derivatives. By using the substances generally employed as the starting point for the common preparations as unknowns, the student will very likely prepare the usual compounds, using the procedures given in the ordinary laboratory manual. Qualitative analysis is found to have the following advantages: 1. It fulfils the purpose of laboratory work, in that it gives the student a first-hand study of the preparation and properties of typical organic compounds. 2. It not only gives the student a knowledge of the fundamental operations, but it develops a valuable technic which tends to counteract the tendency towards carelessness and sloppiness in the organic laboratory, since the preparations are made on a small scale. 3. Yields may be emphasized in this course as well as in the usual one. I n fact, little emphasis is needed on this part of the work, since the unknown must be used to produce a t least two derivatives in sufficient amount to be turned in as a part of the student's report. 4. It gives unusual emphasis to the fact that the library is an important part of the laboratory. We have never seen anything which stimulates as much searching of the literature as such a course does. 5. Just as in inorganic chemistry, the student is taught through qualitative analysis that the cations may be separated by the use of the properties which depend on the structure of the atom, so in organic qualitative analysis, the student is taught the fundamental conception that he is dealing with the architecture of molecules. Since group reactions precede specific tests, the student learns the r61e that each group plays in determining the properties of the molecule. When he begins to see organic chemistry from this viewpoint he is beginning to see the real thing. Many students will complete a course in organic chemistry, without having even glimpsed the marvelous relations between the compounds which go to make up what has been properly called a system of organic chemistry. When the student learns that entirely new compounds may be prepared by
using a few simple general principles, organic chemistry ceases to be to him a plaything of the immortals. 6. The student's whole attitude is changed, so that even the fine print in his text is carefully read over, to see if it will not shed some light on his immediate problem. 7. The student's interest is enlisted. The laboratory work is no longer a proposition of filling so many bottles and banding them to the instructor a t the end of the course. It now becomes a series of projects, a great game which appeals to such primitive instincts as hunting and ambition. The student is never satisfied until he has completely gratified his curiosity about the contents of his unknown bottles. His curiosity is soon replaced by a feeling of power in handling problems in organic chemistry.
Some Practical Points We use Clarke's "Handbook of Organic Analysis" as the laboratory text. MuUiken's "Identification of Organic Compounds" is almost indispensable for reference work. Every book that we can obtain on organic chemistry is eagerly examined by students who are looking for clues that will help them as they pursue their unknowns. All of the important laboratory manuals should be available, and as many other books of reference as library funds will permit. Ten unknowns are issued in the study of aliphatic chemistry during the first half of the course, and ten unknowns'are issued in the study of aromatic chemistry. The more ambitious students are allowed to analyze one or more mixtures a t the close of the course, if time permits. It is of course understood that such a course in organic qualitative analysis, should not be made too complicated. This is largely controlled by the type of unknowns selected.
Moth-Prookg Solutions Tested by Scientist. Clothes moths really'do have a hard time chewing up woolen cloth and other fabrics of animal origin that have been impregnated with one of the various mothproofing solutions now in wide use, according to Dr. E. A. Back of the bureau of entomology of the U. S. Department of Agriculture. It is misleading, however, t o offer an absolute guarantee of protection, he states, and the common method of merely spraying the fabrics confers but little protection. The only way to do the job thoroughly is to wet the cloth through while it is still in the whole piece, and many manufacturers have installed special machinery for this purpose. One of the favorite and most widely advertised moth-repellants consists of 97 per cent of water with 3 per cent of sodium aluminum silicon fluoride dissolved in it. Though this solution sells a t a very high price under its copyrighted trade name, it really does work, if thoroughly applied. Another newly marketed class of compounds is made up of the cinchona alkaloids, chemically allied t o quinine.Science Service
