S. WEINER University of Minnesota, Duluth, Minnesota
TEE pedagogic value of qualitative analytioal courses, both inorganic and organic, has been defended and depreciated. Among the adverse criticisms is that in industry and postgraduate work there is little use for inorganic qualitative analysis or any skills developed therein. Without commenting on the utility of qualitative analysis as a teaching tool for fixing descriptive matter previously presented or on its other possible advantages, certain comments on industrial qualitative analysis are here offered. Many of the qualitative tests learned by students are in constant use in industry as routine control tests, often performed by employees with little training-the %ydrogen-sulfide test for traces of heavy metal ions in pharmaceutical products, nephelometric determination of traces of sulfate or chloride, and the l i k e b u t these are not industrial qualitative analysis. The latter is the identification of the constituents of unknown mixtures and though only a small fraction of the chemists engage in it, it is often as important as it is interesting. The components of a commercial mixture may. have to be identified in support of a patent infringement suit. A proprietary medicine may be analyzed as a step in a prosecution under the federal laws. A trademarked material may be analyzed for a client who plans to enter the business as a competitor or who wants to know why a new competitive article is eating into his sales. The average chemist (or chemistry teacher) has often been asked by a n a b e layman to "analyze this for me, so I can make it myself in my basement," and often the layman's ambitions have been shattered by the fee asked for what seems to him to be a simple though mysterious job. But in industry, law, medicine, anthropology, and chemical research, qualitative analysis is often performed for serious and well-considered purposes that justify the difficulties of such analyses, difficulties not observed in the qualitative courses in colleges. The distinction between organic and inorganic is not nearly as sacred outside the classroom as it is in the school. Whereas "qualitative" in the curriculum usually means inorganic qualitative and is taught with complete independence of organic chemistry, the industrial analyst must usually count on organic and inorganic compounds appearing together and must adjust his isolation methods to this possibility. In some highly competetive industries it is normal practice for the firms to mix organic and inorganic compounds intentionally to hamper analysis by employees of rival h s . Even where this is not intended, practical considerations may require a mixture difficult to separate and purify by orthodox methods.
Most photographic developers are a mixture of sodium sulfite (or bisulfite), a substituted phenol or paraformaldehyde, borax, sodium carbonate, and other salts. Colored smoke grenades may contain a mixture of lactose, potassium chlorate, and an anthraquinone dye. A mildew preventive may contain a copper salt of naphthenic or fatty acid in a hydrocarbon solvent; the decomposition of the metal salt may be a prerequisite to beginning the identification of either. A rust solvent may be a mixture of water, denaturated alcohol, phosphoric acid, alum, lactic acid, and a sodium alkyl sulfonate. A soldering flux may contain zinc chloride, ethanolarnine, isopropanol, and ammonium chloride. Moreover, many of the components are indefinite materials, not even discussed in classes. The organic qualitative "unknowns" usually do not include stoddard solvent, the skellysolves, the industrial denatured alcohols (e. g., "shellacol"), or the other mixtures used so largely in industry. The medium-molecular-weight polymers, waxes, proteins, natural oils and essences, dextrins and sirups are among the other popular ingredients that can "foul up" an analysis aimed a t separating individual compounds from the mixture. Where the indefinite material is merely a solvent for a single compound chemically different in properties the separation is comparatively easy, but in any complex mixture where two or more indefinite ingredients overlap in both physical and chemical properties the quantitative separatiod may be impossible and the identification may have to depend on color, odor, turbidity, viscosity, knowledge of the past practices of the trade, and the price charged for the final article! Where adequate analytical methods exist for such mixtures they usually were developed empirically and are described only in specialists' handbooks; valuable time may be lost in following the methods recommendable for simple organic mixtures. For example, subjection of a popular industrial "antiseptic" mixture to orthodox organic qualitative analysis showed it to consist of chloroform to the extent of 97 per cent. The remainder was a viscous oil of indefinite composition and varying volatility, difficult to characterize. Fortunately, its marked odor had immediately exposed it as camphorwood oil and it was not necessary to embark on a tedious attempt a t separation of constituents. A few physical tests soon confirmed its identity. In classes in qualitative analysis it is more important to find the major constituent than the minor. In industry the analysis of a product may give no useful information to the client if the analyst overlooks ingredients
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that may be vital to the success or popularity of the product but present to only a very small extent. One tenth of one per cent of an acid-stable wetting agent in a metal-pickling mixture may be the "something new" that has been added to secure a speed of descaling and rust removal not achieved by other pickling mixtures. High shelf-life of a dairy product may be due to 0.01% of a powerful enzyme inhibiting oxidation. Small amounts of anti-oxidants, anti-enzymes, dispersing agents, or sequestrants may be the most important ingredients from the client's viewpoint but may be missed completely unless the analyst suspects their presence and aims to prove or disprove his suspicion. Should he find indications of such small ingredients, and feel sure they are not impurities due to the use of commercial. grades, his knowledge of the usual properties of the expcrted auxiliary and of the nnnlytirill twl~niqucsin the indnstrv will rmi~~t 011t to him thc scunration und identification methods best for this case. ' In some cases an impurity may be sought as a clue to the source of the main ingredient. Commercial and government analytical methods are often designed to this end. A chance case is the following. A material popular in the beverage industry was found to contain K+, NH&+,SO3=,SO;, an enzyme, a carbohydrate, and a minute amount of brown slime. The inorganic constituents were shown to be potassium metabisulfite with the ammonium sulfate present as a chance impurity. Except for the very small brown slime, all substances were water-soluble and ether-insoluble. The chemist believed from his past experience that the carbohydrate was dextrose, but a qualitative test gave a positive though weak indication of pentoses or levulose. Feeling sure this was in error, he proceeded to separate the carbohydrate from its companion ingredients with an extraction solvent adapted for dextrose and found it to be indeed dextrose. The isolated sugar, of course, gave no test for levulose. The client was dissatisfied
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with the qualitative and quantitative data that was finally given him; he wanted to know also the source of the enzyme. The chemist, recalling the weak indication of "levulose," suggested the source was vegetable and specifically named a tropical plant from whose stems a latex is expressed that is a commercial source of this enzyme; he believed that traces of plant fiber containing pentosans had accompanied the enzyme and had caused the false test for "levulose." An associate gave reasons for believing the enzyme to be of animal origin. Examination under the microscope revealed the square cells of cork fragments and the ladder-like threads of stem fibers. These fibers composed the insoluble slime. The problems met with in industrial qualitative analysis are so different from those presented to students in either organic or inorganic qualitative analysis that the lattcr t\vo courses h a w only diglrt pr:~rticalvalue for nmwndemir work. This Irxwr as the ohierti\.r. o.f the qualitative courses the inculcation of physicochemical principles, techniques of separation and purification, properties of the elements and the important ions, and characteristic reactions of organic functional groups. Should a student of inorganic qualitative ignore the physical principles, e. g., the ion-product-constant rule, as "merely theory" it can be pointed out to him that this principle will be useful to him in a later course, whereas the qualitative detection of an element will not be a likely problem in later years nor will it alone help greatly in the solution of such qualitative problems as may arise. The qualitative problems in industry require a higher degree of versatility and flexibility. If the course is a teaching tool for the aims mentioned above, the difference between the approach taught in the course and that required in practical problems should be pointed. This should be done either very early in the course to prevent neglecting the "theory" or a t its very end to remove any complacent feeling that "now I can analyze andsolve practical problems."
