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 at 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
NOVEMBER 1947
933
The formation of the hydroxamate is greatly influenced by temperature. Thus, at 110” C. the sodium hydroxamate in the reaction flask is completely destroyed on continued heating after the vessel is dry. At 55’ C. the flask may be heated for several minutes with little change in the intensity of ferric hydroxamate obtained. \Tide fluctuations in room temperature influenced the intensity of color, apparently through the cooling effect of the small quantity of reflux remaining in the flask. The effect of fluctuations in room temperature can be obviated by introducing solution A into the reaction flask without delay after the 5-second drying period or by cooling the flask in cooling tray before introducing solution A. The hydroxylamine hydrochloride and sodium hydroxide solutions may be conveniently added dropwise from a glass-stoppered dropping bottle; when stored, need not be renewed for a week. When organic or mineral acidity or alkalinity is present, the
solution must first be neutralized. The ratio of reagents is not critical; thus the volume of sodium hydroxide may be increased by 50y0even in neutral solutions, with little effect on the color formation. Ester values obtained by the above procedure on 1-mg. samples are shown in Table I compared with values obtained by the methods of the Association of Official .4gricultural Chemists ( 1 ) . The method has been successfully applied in the determination of sulfated esters. The term “ester value” used here is as defined by Jamieson ( 3 ) . LITERATURE CITED
Official Agr. Chem., Official and Tentative Methods of Analysis, 4th ed., pp. 412, 417 (1935). (2) Hill, C . T., IND.ENG.CHEM., ASAL. ED.,18, 317 (1946). (3) Jamieson, G. S., ”Vegetable Fats and Oils,” p. 340, New York, Chemical Catalog Co., 1932. (1) Assoc.
RECEIVED Sovember 15, 1946.
Determination of Thallous Chloride in Solutions of Thallous Decanesulfonate JOHN C. HENNIKER’
AND
E. C. LINGAFELTER, University of Washington, Seattle, Wash.
K’ T H E course of a n investigation of activities in solutions of Ideterminations long-chain alkanesulfonates, it was desired to make accurate of the solubility of a sparingly soluble salt in a solution containing an alkanesulfonate. Both thallous iodate and thallous chloride had been found suitable in similar studies (2, 3 ) . Since it Fas necessary for the cation to be common to both the sulfonate and the sparingly soluble salt, the problem narrowed t o the determination of iodate ion or chloride ion in the presence of a thallous alkanesulfonate. Attempts to use the iodate were unsuccessful because of the poor end point in the iodine-sodium arsenite titration in the presence of the alkanesulfonate. For the determination of chloride-ion concentrations, the Mohr method was eliminated because a bulky yellow precipitate of thallous chromate obscured the red silver chromate and could not readily be removed. Titration to the “clear point” was impossible because the colloidal nature of the sulfonate ion prevented precipitation of silver chloride. The Volhard method was not suitable, since the impossibility of quantitatively removing the silver chloride from these solutions caused a fading end point. Attempts were made to destroy the sulfonate ion by combustion, but such a high temperature was required that even thallous sulfate was decomposed. Attempts to destroy the sulfonate ion with various strong oxidizing agents were unsatisfactory. However, a method was evolved for precipitating silver chloride from sulfonate solutions for weighing on a semimicro scale. When the solution was 0.3 N in nitric acid, precipitation was rapid as long as there was an excess of chloride ion, but when there was as little as 0.0016 N excess silver ion, no amount of digestion gave quantitative precipitation. The method finally adopted was to add the last of the silver nitrate in increments of 5% of the total, digesting after each addition until no more precipitate was formed. Digestion a t 100°C. for one hour ensured quantitative precipitation in a readily filterable form. As a check on the method, known amounts of thallous chloride were determined in the presence of thallous decanesulfonate. Agreements to within 1%in a solution 0.001 N in chloride were obtained. This action of the sulfonate is probably due to the adsorption of (negatively charged) alkanesulfonate ions on the surface of the (positively charged) particles of silver chloride in the presence of excess silver ion. This adsorption would not occur on the particles in the presence of excess chloride ion. A further illustration of the protective colloid action of a long1 Present
addreas, Paraffine Companies, Inc., Emeryville 8, Calif.
Table I. Thallous Chloride in 0.02 N Thallous Decanesulfonate Solution at 35’ C. Kormality of Thallous Chloride ( X 103) Cnsaturated Supersaturated 18.14 5.68 17.97 9.08 16.66 12.72 16.43 14.02 15.40 14.30 15.01 14.52
Days of Agitation 1 3 12
31
45 60
chain alkanesulfonate was provided by the manner in which equilibrium was approached between solid thallous chloride and an aqueous solution of thallous decanesulfonate. The solid was agitated for several weeks with sulfonate solutions both unsaturated and supersaturated with respect to thallous chloride. Data for a sulfonate concentration of 0.02 K appear in Table I. The temperature mas 35’ C. The rate of crystallization has been inhibited even more than the rate of solution. The possibility that these effects of thallous decanesulfonate might have been due to some property peculiar to this salt rather than to the sulfonate ion alone was eliminated. First, the conductivity of thallous decanesulfonate solutions was traced up to 0.05 N . The data showed a conductivity-concentration relationship similar to the calculated Onsager slope, followed by a sharp drop in equivalent conductance at 0.030 h’,the concentration expected for the formation of micelles ( 5 ) . I n addition, the value of the limiting equivalent conductance (114.0) agrees satisfactorily with the sum of the limiting ionic conductances (117.0) of the decanesulfonate (5) and the thallous (1) ions. All these data show the thallous salt to be similar to other decanesulfonates that have been investigated and found to be strong electrolytes up to a critical concentration ( 4 ) . Secondly, the possibility of slow deterioration of the thallous decanesulfonate was disproved by holding a solution of the salt a t the boiling point for a n hour. The conductivity was not changed by this treatment. LITERATURE CITED
(1) International Critical Tables, Vol. 6, p. 230, New York, McGraw(2)
Hill Publishing Co., 1926. La Mer, V. K., and Goldman, F. H., J. Am. Chem. SOC.,51,
2632
(1929)
(3) Stone, G, C. H., Ibid., 62, 572 (1940). (4) Tartar, H. V., and Wright, K. A., Ibid., 61, 539 (1939). (5) Wright, K. A , , Abbott, A. D., Siverts, V., and Tartar, H. Ibid., 6 1 , 5 4 9 (1939). RECEIVED December 11, 1946.
