A LIBRARY PROBLEM IN QUANTITATIVE ANALYSIS M. 6. MELLON Purdue University, Lafayette, Indiana
INTEE course of buying, makmg, using, and selling of the' number desired and in any relative amounts, materials, modern chemical industry operates largely on might be assigned. The combinations and possibilities 'the basis of laboratory tests and analyses. The major are almost unlimited when one contemplates all the part of the data is obtained by standardized, routine elements, radicals, and compounds known, together methods, and the workmay be highly repetitive. Under with all the naturally occurring substances. Thus, some competent supervision determinators are much used in 400,000 organic compounds alone have been prepared. such cases. An example is the steel mill, producing lain carbon steel. where dav after dav hundreds of -FACTORS INVOLVED - - - - - - ~. . - ~ ~ determinations are made for carbon, manganese, A method of analysis intended for determining several phosphoms, silicon, and sulfur by means of well-known constituents in a given sample will depend upon a num--A,.a,,IrLGUIVU~. ber of factors, such as the following: In contrast to this routine analytical problem, that 1. Amount of Sample. Small amounts of sample presented by alloy steels may be relatively complicated. In the latter material it is now common to find from two may necessitate micro or even ultramicro methods. to five, or more, elements other than the "big five" Otherwise, macro methods are generally less exacting in already mentioned. If these constituents should be requirements of skill and equipment. 8. Composition of Sample. Devising a procedure for chromium, molybdenum, titanium, tungsten, and vanadium, for example, the high-school determinator determining desired constituents presupposes knowing trained for the titrimetric method for manganese would what they are. Each chemical element, radical, and compound has its olvn individuality in terms of-proper. hardly know what to do. Many products, such as ferrous and nonferrous alloys, ties which must be taken into account in any method. 3. Amounts of Desired Constituents. Whether the now contain a number of elements once uncommon. Such added constituents usually complicate the analyti- desired constituents are present in major or trace cal procedure. A strikmg example is the recent use of amounts must be known or determined. This is because about a thousandth of a per cent of boron in certain methods for traCe constituents; such as emission specsteels. To meet such a resulting analytical problem, trometry and currentometry (polarography) are limited there is needed an analyst with a broad knowledge of to low ranges of composition. 4. Accuracy of Results Required. If nothing less than the facts of chemistry and physics which are relevant to the situation a t hand. The chemistry is that required to the highest attainable accuracy will suffice, one must bring the desired constituents into'condition for meas- use the method capable of yielding &ch results. Often, urement, and the physics is that underlying the instm- however, such data are neither desired nor worth while. ment and its use for the required measurements. ' T o If so, a less exactmg method should be the choice. 6. Time Required for a Determination. To an inmeet a new situation, the analyst may be able to adapt an old method or he may have to devise a new proce- .creasing extent in industry speed has become almost the dominant factor. I n such a case the most rapid dure. In attempting to get seniors and graduate students to method is desirable, provided its reliability will suffice. 6. Apparatus and Services Needed. Many newthink through the problems involved, the author has found difficulty even when the discussion dealt with methods require expensive apparatus and unusual well-established procedures, such as those for brass or operating facilities. As yet only the most modern and limestone. Many individuals seem to forget the pos- well-equipped laboratories may be expected to have sible effects of the presence of one constituent upon the items such as a quantometer, a mass spectrometer, or a determination of another, particularly when separations photoelectric spectrophotometer with a Miiller-Hilger are involved. That this and other important points double monochromator. Specificationof such methods often are not realized or taken into account has become is out of the question, therefore, in many laboratories. 7. Skill of Operating Personnel. Methods employincreasingly evident in the course of having students devise a method for given constituents and present a ing involved chemical transformations and intricate report of the proposed procedure. The purpose of this measuring apparatus necessitate more competent perpaper, therefore, is to suggest a library problem designed sonnel than simpler procedures. As a rule, the simpler to give the student some simple experience in suggesting the measuring equipment and the processes of treatment a procedure based on facts to be found in the literature. and separation, the more easily the whole method may Presumably any system of compatible constituents, be routinized for determinator persoqnel. 283
