Progress Report of Committee on Naming Analytical Methods
T
HE progress of chemistry during the past century has brought many problems of nomenclature as investigators have tried to designate systematically their vast numbers of compounds and methods of operation. -4s a result of unified effort, we now have the I.U.C. system for naming compounds in organic chemistry, and a tentative, comparable proposal for inorganic
using the process generally ends with some measuring operation. I t is a particular kind of adsorption separation (differential or columnar?). The prefix chromo- implies hue, yet there map be no hue in the system. The suffix -graphic presumably should have the dictionary meaning, (a)combining form signifying something written, or ( b ) combining form signifying an instrument for making or transmitting records. Strictly, then, Ti-hat does ehromatographic mean? 4 recent effort to use the word “instrumental” is a curious phenomenon. I t s proponents mean t o differentiate certain analytical methods, such as optical, from others, such as gravimetric. Yet, is it not clear by definition that all measurement involves use of a measuring instrument? Certainly an analytical balance is an instrument of measurement. Since all measurements are instrumental, the term is inclusive rather than exclusive. 111. Current Naming of Quantitative Analytical Methods. I n order to show more systematically the variations in current usage of terms to name or indicate analytical methods, the aecompanying outline has been arranged from examples t o be found in wellknown publications, some of n-hich exhibit amazing individual inconsistencies.
a1 chemistry has been less fortunate. S o such system having been adopted for its many operations and methods, the literature abounds in inconsistent and indefinite usage of terms. Analysts have been little better than others in this practice. The appointment of the present committee !$-as requested by H. E. HoTve, late editor of Industrial and Engineering Chemistry, who recognized the difficulties arising from the lack of standards, or of adherence to standards, in analytical IT-riting. Consequently, the committee has taken as its assignment the proposal, ii feasible, of such standards of practice to the Division of -4nalytiral and Micro Chemistry. If approved, these should then become a basis of recommended practice fo’r the editor and reviewers in dealing with manuscripts presented for publication. Dissemination of such recommendations, combined with cooperation of reviewrs and authors, should improve future publications.
(Procedure designated in terms of) EXAMPLE OF ZiSAGE
1. The originator(sl of the method. a. The individual(s1-e.g., Kjeldaiil method. b. The institution or laboratory-e.g., Harvard, or Bureau of )lines method. 2 . The organization approving the method. a. S a m e onlv-e.g., U.S.P. method. b. S a m e and status of adoDtion-e.a., A.S.T.11. offici’al or tentative method. e. S a m e and applicability-e.g., rl.0.A.C. general or special method. d. S a m e and number-e.g., d.P.H.d. method I . 3. The kind of material analyzed-e.g., steel analysis method. 4. The physical state of the sample-e.g., gas analysis mct,hod. (Fasometric is often used, but not its coordinates, liquidonietric and solidometric.) 5 . The g ~ ~ n e r conditions al maintained-e.g., n-et, dry, or assay met hod. 6. The magnitude or scale of operations used-e.g., micromethod. 7 . The kind of general physical method used-e.g., mechanical, electrical, or ultrasonic method. 8. The effect or action of the desired constituent-e.g., polarization or emanation method. I). Thc instrument used a. I n preliminary treatment of the sample-e.g., Parr bomb met hod. b. I n separation of the desired coiistituen-e.g., vacuum oven method. c. 111meaimement of the desired constituent-e.g..- . refractometer method. 10. Thi, principal reagent used a . I n preliminarj- treatmpnt of the sample-e.g., peroxide fusion method. b. I n separation of the desired constituent-e.g., nitron method. c. I n mcasurement of the desired constituent 1. Class of reagents-e.g., acidimetric method. 2 . Specific reagent-e.g., iodometric method. 11. The property measured in determining the desired constituent a. A specific property-e.g., gravimetric method. b. .1systemic property-e.g., densimetric method. 12. The principal single operation or process used a. I n preliminary treatment of the sample-e.g., fusion method. b. I n separation of the desired constituent-e.g., electre lvtic method. c. I n measurement of the desired constituent-e.g., titration
In .order to emphasize the problem, it seems desirable to give some examples of current practice. N o effort has been made to compile an exhaustive list of such things, but the items included are believed to be representative of what is being done. I. Introduction of New Words. An expanding and changing subject, such as chemistry, requires nen- terms. \Then they are necessai’y, either t o designate neiv things or to bring previous inconsistent usage into line, there should not be objection. We do need standards of practice, however, to guide those introducing such terms. As examples of current development., the folloiving viords may be cited: azotometry, colaminometric, interferentiometric, iodohydragyrometry, luximeter, oncometer, photelgraphic, polaristrobometric-chemical, riptographic, nnd thermoponderonietric. Are these appropriate? Do they conform to good naming practice? A reader may well wonder. 11. Questionable Usage. Some terms are old and by now should be clearly established in our thinking. Much current ivriting indicates, however, that this is not true. Several examples are of interest. The n-ord “analysis,” in its quantitative aspects, seems a t times misused. Thus, the analysis of aluminum should n-ean the determination of the minor constituents in aluminum metal, and not the determination of aluminum in something else. Potaszium is not “analyzed” as the chloroplatinate. The word gravimetric should mean measurement by mzss (\\.eight). Used in this sense, there is obviously no implication concerning any particular kind of method of separation employed to prepare the material for neighing. Yet some writers apply the ~ o r only d when the materials are separated b y precipitation, a limitation that relegates to the “special” class such determinations as water in barium chloride dihydrate by heating and weighing the nonvolatile residue. And in extreme cases it is stated that the ion product principle must apply to the precipitate. l l u s t one conclude, thcm, that a procedure involving the handling of a precipitate of mctallie platinum is a “special,” rather than gTavimetric, method? Thcre seems no logical reason for excluding from the gravimetric group procedures in Jvhich the material t o be weighed is separated by volatilization, extraction, or electrodeposition. The expression “chromatographic analysis” is disturbing. It docs not, of course, refer t o any kind of measurement, although one
I
931
,
V O L U M E 19, NO. 1 1
932 metric precipitation, volumetric extraction, or manometric volatilization method. PRELIMlNARY RECOMMENDATION
The broad objective of any analytical nomenclature should be to label objects and processes for the recording and transmission of ideas as accurately, clearly, briefly, and consistently as possible. The basis should be simple, readily usable, logical, and comprehensive. I t must be expected] of course, that the replacement of unsystematic practice by systematic usage will probably require disapproval of certain current terms and approval of others less familiar, for a changing science brings changing concepts and nomenclature. A notable example of this is the present struggle of physical chemists to define an acid. Since analytical nomenclature uses words, it seems highly desirable, first of all, to agree_upon meanings for a number of terms widely used, such as accuracy, analysis, light, and precision. Strictly, these words are not involved in naming methods; but they are used in connection with methods, and should have a clcar and definite meaning. Having defined these words, the
committee may then take up those dealing with operations and instruments as a preliminary to making recommendations for systematizing the nomenclature of methods of analysis. In defining suchterms, the present intention of the committee is to formulate a series of statements comparable to those published by two other societies. A committee of the Illuminating Engineering Society, under the chairmanship of E. C. Crittenden, has prepared ( 1 ) such statements as its “Illuminating Engineering Nomenclature and Photometric Standards.’] Similarly, a committee of the American Society of Plant Physiologists, under the chairmanship of R. B. Withrow, has made comparable recommendations ( 2 ) in its “Radiant Energy Nomenclature.”
S. E. Q. ASHLEY S. H. FURMAN H. V. CHURCHILLL. T. HALLETT M. G . MELLON,Chairman H. C. DIEHL LITERATURE CITED
Crittenden et al., Illum. Eng. SOC.,A S A Report 27.1 (1942) (2) Withrow et al., Plant Physiol., 18, 476 (1943).
(1)
Colorimetric Determination of Fatty Acids and Esters UNO T. HILL, Inland Steel CompanJ., East Chicago, Znd.
RECEXT contribution (2) indicated that the colorimetric
A. ‘procedure used for the estimation of fatty acids and esters could also be employed in the estimation of hydroxyl numbers, acetyl values, and saponification numbers. An improved procedure has since been developed in this laboratory for the determination of oil content and ester values from a single curve. By the proper choice of constants other values based on the ferric hydroxamate color may be estimated. EQUIPMENT AND REAGENTS
A Coleman Model I1 spectrophotometer is used. The reagents are the same as previously described ( 2 ) except that solution A is made as follows: Dissolve 0.4 gram of iron or an equivalent amount of iron as ferric chloride in 20 ml. of 1 to 3 nitric acid, add 15 ml. of 79% perchloric acid, and heat to copious fumes of perchloric acid. Cool and transfer to a 100-ml. volumetric flask with the aid of 40 ml. of water added from a pipet. Add 10 ml. of concentrated nitric acid and dilute to the mark with 70% perchloric acid. Make a 1% solution of this in 95% ethanol or 95y0 methanol. The akoholic solution is stable for a week or more, while the stock solution keeps indefinitely. PROCEDURE
The procedure is the same as previously described ( 2 ) except that 10 ml. of solution A are added immediately a t the end of the 5-second drying period, in order to avoid variations due to fluctuation in room temperature. The contents of the flask are adjusted, to 27’ C: and the color is obtained against either water or a blank. For highly colored oils it is necessary to add to the blank an amount of the colored oil equivalent to that used in the sample. This is done after solution A has been added, since the oil is incapable of forming hydroxamic acid a t this stage.
Using cottonseed oil as a standard and calculating the value of
C, the above equation for all oils reduces to:
”.
Ester value = 363
DISCUSSION
The fading of the ferric hydroxamate complex ( 2 ) was found to be caused by an excess of hydroxylamine which reduced the ferric iron needed in the production of ferric hydroxamate. By introducing an oxidant into solution A the excess of hydroxylamine could be destroyed without interfering with the desired colored complex. Thus if 1% of 3Oy0 hydrogen peroxide was added, the color was stable for 3 days. Colors produced Jvith solution A containing nitric acid are not so stable, but more accurate results are obtained than when hydrogen peroxide is used. Stabilization can also be effected by filtering the colored complex through filter paper or by soaking filter paper in the alcohol used in preparing solution A. Ether used as a solvent for the esters should not be allowed to come in contact with filter paper, since considerable quantities of esters are extracted from the paper; this leads to excessively high values.
Table I. I
Transniittancy values for all oils can be expressed by the following straight-line equation: =
ester value of standard (2.0 - log 7’) ester value of unknown X C
where T = per cent transmittancy and C curve.
=
slope of standard
(2.0 - log T ) mg. of sample
By the choice of proper constants, other values may be obtained from this single curve.
CALCULATION
Mg. of oil
(2.0 - log T ) Mg’ Of Oil = 363 ester value of unknown
Kind of Oil
Ester Values-
SaponiI1 fication No. Acid Value (A.O.A.C.) (A.O.A.C.)
1
__
- I1
Ester Value, Saponlfication
Ester Value, Colori. metric
