INDUSTRIAL AND ENGINEERING CHEMISTRY
154
of ferric alum, the exact iron value of which need not be known. Apparently the less rubber tubing used between the storage bottle and the buret the better. The cause of the harmful influence of the tubing has not been definitely determined, however. Potassium thiocyanate may be successfully used as an inside indicator, for the determination of iron a t least. From 1 to 10 cc. of a 10 per cent solution may be used, 5 cc. being enough. The end point is a little easier to determine when 5 cc. are used than when only 1 cc. is used. Ferrous ammonium sulfate bought in the open market cannot be relied upon to serve as a satisfactory primary standard
Vol. 19, KO. 1
for titanous sulfate solutions. The same is true of the ferric oxide tested in the experiments here discussed. Sibley iron ore as put out by the Bureau of Standards with analysis appears to be a reliable primary standard for titanous sulfate solutions. It may be prepared for titration without a great expenditure of time or effort. Ferric alum, its oxidation carefully made complete with permanganate, is a very satisfactory secondary standard. Even if another ultimate standard is used, a solution of ferric alum is convenient for occasionally checking the permanence of the titanous solution and quantitatively measuring any changes it may undergo, even though the exact iron value of the ferric alum is not known.
Applicability of the Indirect Method of Analysis to Determination of Sodium and Potassium in Soil Solutions’ By Ray E. Neidig and W. B. Bollen DEPARTMEST O F AGRICULTURAL CHEMISTRY,UNIVERSITYO F IDAHO,A N D AGRICULTURAL EXPERIMENTSTATION,Moscow, IDAHO
I
N THE study of alkali soils at the Idaho Agricultural
Experiment Station numerous determinations of sodium and potassium must be made. The gravimetric methods now in use are so time consuming as to be almost prohibitive where many determinations are required. The necessity for a simple and more rapid method led the writers to investigate the indirect method of calculating the amounts of sodium and potassium from the weights of their mixed chlorides and total chlorine. The indirect method of analysis has long been known, but, as CrookesZhas remarked, i t does not appear to possess the confidence of chemists and is rarely mentioned in published investigations. As to its reliability, Crookes states, “From a long list of analyses it is shown that the indirect method is in all cases equal in accuracy to the ordinary (platinochloride) separation, while in the matter of convenience and economy of time there is no comparison between them.” Earlier work on indirect methods of analysis is reviewed in a recent article by C ~ m e l l a . ~ This author also introduces a graphical method based on arithmetical progression, and develops formulas permitting independent calculation of the constituents of a homogeneous binary salt mixture. Comparative data obtained by these and other formulas from several series of analyses made on knowp solutions of potassium chloride and sodium chloride are not concordant. Apparently the discrepancy is due, partly to factors calculated on obsolete atomic weights, and partly to calculation of potassium chloride independently of sodium chloride by the author’s method, or else to errors in transcribing. Independent calculation of the components of mixtures of two, or even more, homogeneous salts is possible with other formulas, and from the standpoint of error distribution this is preferable to the more convenient method of calculating one salt by difference. Development of F o r m u l a
Formulas for a two-salt mixture are readily derived as follows: 1 2
Received August 17,1926. “Select Methods in Chemical Analysis.’’ p. 20, Longmans, Green &
Co., 1886. 8 Ann. ckim. a p p l i c a f a , 15, 123 (1925); C. A . , 19, 3441 (1925).
L e t x = NaCl v = KC1 = (NaC1 KC1) G = total C1 a = 0.6066 = C1 factor of NaCl b = 0.4756 = C1 factor of KC1 Then x + y = s ax by = c From (1) y = s - x Substituting for y in ( 2 ) ,
,:
+
+
+
ax b(s-x) = c 2 l n - h )-, = r- - h s- - - \ -
C-0.4756s - c-0’4756s = 7.6336~- 3.6305s 0.6066-0.4756 0.1310 or NaCl = 7.6336 C1-3.6305 (NaC1 KC1) or Na = 3.0031 C1-1.4283’(NaCl.+ KC1)
c-bs
=
a-b
+
’
I n like manner it can be demonstrated that
+ KC1)-7.6336 C1 + KC1)-4.0030 C1
KC1 = 4.6306 (NaC1 or K = 2.4282 (NaC1
These formulas are essentially the same as those given by Crookes, except that the factors are based on atomic weights from the International Critical Tables. Inspection of the formulas shows that any errors made in the determination of total salts and chlorine are multiplied by the factors given. This may appear to be a serious defect, but granting a refinement of technic commensurate with the gravimetric determination of potassium the final errors in calculated results need not exceed *2 or 3 mg. By using N/35.46 silver nitrate solution, chlorine can be determined to within 0.1 mg., but allowing a range of error of *0.5 mg. for chlorine and * 1mg. for the weight of salts, the errors in calculated amounts of sodium and potassium would not exceed the values shown in Table I. This range of accuracy is satisfactory for our class of soils work, where the error in milligrams rather than in per cent is given first consideration. Errors of analysis in the same direction tend to compensate each other, while opposite deviations rapidly increase the errors in calculated amounts of bases. To insure tolerable errors it is therefore essential to avoid increase in weight of the purified salts by contamination with foreign matter or by incomplete drying. When one salt is absent, or present in very small amount, its calculated value may be negative. A negative value of not over 1 or 2 mg. may be taken as zero, while large negative values indicate a serious error in the analysis.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
January, 1927
Table I-Errors in Calculated Amounts of Sodium and Potassium Resulting from Permissible Errors in Determined Amounts of Salts and Chlorine Na = 3.0031C1-1.4283(NaC1
PERMISSIBLE ERRORS (NACL-I-KCr,) CL Mg. Mg.
+ KCI);
ERRORS IN
CALCD.NA Mg.
0 0.5 70.5
*l *l *1
+4.0030 KC1)CI
K = 2.4282(NaCI
T
1.4
T
2.9
ERRORS IN CALCD.
K
Mg.
d=
4.4
Testing of Method
The method was tested by applying it to a series o f solutions containing known amounts of potassium and sodium chlorides. The solutions were prepared from standards made up with double distilled water and oven-dried salts of H-ion quality, calibrated apparatus being used throughout. Potassium in several dilutions of the chloride solution was also determined by the chloroplatinate method. From the results given in Table I1 it is seen that, while the errors exceed 2 mg. in a few instances, they average less than 1 mg. The error in calculated values for sodium is usually less than in those for potassium.
155
The variation in magnitude of error appears to be fortuitous, depending on manipulation rather than on the N a : K ratio, actual or relative. Comella and others4 regard the indirect method as inapplicable where one salt of the mixture is much in excess of the other, because the errors increase rapidly as the ratio of the bases approaches its limits. It is true the per cent error soon becomes intolerable under these conditions, especially if 0.1 N silver nitrate solution is used in determining chlorine. By using N/35.46 silver nitrate solution the present authors were able to determine chlorine within an average of 1 0 . 2 mg. This made the weighing of salts the limiting factor in determining the amount of error in calculated amounts of sodium and potassium, and with an average error of *0.6 mg. in the weight of salt mixtures the errors obtained ran from a few tenths of a milligram to the extreme of only 3.4 mg., regardless of the Na: K ratio. Moreover, as shown in Table 111, the chloroplatinate method, with the same degree of accuracy in manipulation, gave errors of the same order. It is concluded, therefore, that the applicability of the indirect method is limited only by the degree of accuracy of the analyses. Table 111-Determination
of Potassium as Chloroplatinate
ERROR
K FOUND Mg.
K TAXEX ME.
Mg.
~
Table 11-Indirect
AMOUNT TAKEN
RATIO
$,:
NA:KorK:NA 0 : o to 100
0 0 0 0 0 0 0
0
0 1 5 10 10 50 100 1:l
1
1 1 5 10 10 10 50 100 100
1:2
1:5
1: 10
0 1 1 5 10 10 50 100 100 0 0 0 0 0
NA Mg. 0 0 0 0 0
0
0.3 0.3 0 0 0 0.3 0.8 0.4 -0.8 -1.2
1 1 1 5 10 10 10 50 100 100
0.3 0.2 0.3 0.7 0.2 0.1 0.4 -0.4 -0.8 0.8
ERRORS
K Mg
0 0 1.2 0.9 0.6 -0.3 -0.4 2.3 1.3 0
0 0 0 1.4 0.3
-0.3 -0.2 0.4 -1.1 -0.3 -0.3 0.4 1.0 2.1 1.4
5 50 50 10 100 100
10 100 100 5 50 50
-0.1 0.1 0.7 -0.1 -0.5 1.3
0.3 -1.1 -1.1 0.2 1.7 -1.7
1 10 10 5 50 50
5 50 50
-0.1 -0.9 1.7 0.2 -0.9
0.8
-0.5 1.8 -2.6 -0.2 1.6 -1.7
1
10 10 10 50 100 100 1 1
-0.5 -0.4 0.2 0.3 0 -2.0 -0.9 0.4 0.8 2.0 0.7 -1.3 -1.1
0.9 0.9 -0.2 -0.4 0.2 3.4 1.7 -0.5 -1.0 -2.7 -1.0 2.7 2.0
0.4 0.1
0.2 0.0
1.7 -0.1
-1.3 0.8
1
,
K
Mg.
1 5 10 10 10 10 10 50 50 100 100
1
10 10
1
5 5
10
10
1:20
5 100
100
1:50
1 50
50
5
1
100 -0.2 1 -1.5 1 -1.1 AVERAGE 0.54
-0.6 -.3.0
1.9 0.97
0.1 1.4 5.6 10.7 50.7 101.6
0.0 1.0 5.0 10.0 50.0 100.0
Determination of Sodium and Potassium in Solutions of Their Chlorides
0.1 0.4 0.6 0.7 0.7 1.6
Analyses of Soil Extracts
A number of soil extracts, freed by standard procedure from all bases except sodium and potassium, and possible traces of rarer elements, and converted to chlorides, were analyzed by both methods to obtain a comparison under usual laboratory conditions. After weighing the mixed chlorides they were dissolved and made up to volume with distilled water; one aliquot was then taken for determination of potassium by the chloroplatinate method, and one for determination of chlorine for calculation of sodium and potassium indirectly. Results are given in Table IV. Table IV-Determination
1 1 2
3 4 5 6
7
8 9 10 11 12 13 14 15
of Sodium and Potassium in Soil Solutions SODIUM
POTASSIUM DIFFERDIRECT INDIRECT E N C E
Mg. 13.3 14.7 5.0 11.4 31.6 10.2 9.9 40.1 37.3 53.1 13.3 11.1 13.2 0.8 1.2
Mg. Mg. 20.1 -6.8 16.6 -1.9 13.2 -8.2 11.3 0.1 30.6 1.0 0.9 9.3 11.3 -1.4 36.4 3.7 31.5 5.8 64.0 -10.9 9.5 3.8 4.9 6.2 4.5 8.7 0.0 0.8 1.8 - 0 . 6
DIRECT INDIRECT
hlg.
60 8.3
55.9 9.4 24.0 7.4 10.2 36.7 30.2 100.6 9.0 5.6 54.6 2.0 2.6
Mg. 54.9 6.9 49.8 9.5 24.7 8.1 9.2 39.5 34.5 92.4 11.9 10.5 58.0 2.5 3.0
DIFFERENCE
Mg. 5.1 1.4 6.1 -0.1 -0.7 -0.7 1.0 -2.8 -4.3 8.2 -2.9 -4.9 -3.4 -0.5 0 4
-
Agreement between the two methods is good in eight out of fifteen examples. The lack of agreement in the other cases may be attributed to error introduced in weight of the salt mixtures by the presence of foreign material, or by possible loss after weighing. While the small unavoidable errors exert a much less influence upon the direct determination of potassium, the values for both sodium and potassium may be more nearly correct as given by the indirect procedure. If the values given by the latter are incorrect,it is probablethat thesame contributing errors of analysis would be introduced into the 4
Olson, “Quantitative Chemical
co., 1915.
Analysis,”
p. 492, D. Van Nostrand
INDUSTRIAL AND ENGINEERING CHEMISTRY
156
chloroplatinate method and throw a still greater error on the sodium as determined by difference. Moreover, the chloroplatinate method is liable to error through numerous conditions not affecting the indirect method.
Vol. 19, No. 1
Except where potassium alone is sought, the indirect method is therefore concluded to be equal to the chloroplatinate method in accuracy, and it is superior in all cases from the standpoint of economy of time and cost of reagents.
Susceptibility of Fats to Autoxidation‘ By Geo. E. Holm, Geo. R. Greenbank, and E. F. Deysher RWEARCH LABORATORIEX~, BUREAUOF DAIRY INDUSTRY, W A S H I N G T O N , D. C.
T
HE deterioration of most fats and oils through reac- of practically no absorption. The nature of this reaction tions involved in oxygen absorption usually proceeds is shown in Figure 2. Further study of this phase of the reaction has not been rapidly once active absorption has begun. At this point, however, the reactions are relatively far advanced, attempted, but the following explanation seems plausible. and tests dependent upon the products of the reactions give Studies upon the nature of the compounds formed in the little or no information concerning the ability of the product oxidation of unsaturated compounds seem to indicate that to withstand oxidation. oxides and peroxides are not the first compounds formed in The Kreis test, the photographic plate image test, and the the reaction.6 To these unisolable products the term peroxidase test are very delicate, but so far have proved LLmoloxides” has been applied. The initial a b s o r p t i o n of no great value in deternoted in a number of cases is mining the susceptibility of a fat to autoxidation. The perhaps due to the formation Evidence is presented of the existence of loosely of such compounds, which last two give evidence of bound oxygen compounds in butter oil. These subbeing directly c o n n e c t e d may be looked upon as loose stances, termed “moloxides,” are undoubtedly reoxygen c o m b i n a t i o n s of with certain changes that sponsible for oxidation in uacuo. The powerful repotential oxidizing ability. occur early in the oxidation tarding action of the OH group in several compounds s t a g e a n d therefore may The exact conditions under has been studied. Data obtained show that the suswhich this initial oxygen abhave some value in deterceptibility of cottonseed oil to autoxidation varies with sorption occurs and may be mining this factor. the commercial treatment. The effect of ultra-violet noted are not known. The curve which illuslight upon the autoxidation of cottonseed oil is shown. T h e foregoing explanatrates autocatalytic oxidation, based w o n the idea tion is logarithmic for most that loosely combined oxyfats (Figure 1). The length of the period preceding the phase of rapid absorption, known gen compounds are formed, receives support also from the as the induction period, varies, however, with the type and following observations: Certain butter oils were always quality of the fat or oil. improved when steam was passed through them for a short In view of the fact that deterioration is rapid after it has times6 Other samples did not respond so readily. A become perceptible, it is most important to know to what sample of a fat that had been steamed and a sample of the stage in the induction period a certain fat belongs. A measure same fat left untreated were sealed in glass containers under of the length of this period under specified conditions there- high vacuum (applied for 30 minutes at 40” C.) and were fore gives a relative quantitative measure of the ability of a placed in sunlight. The untreated sample bleached rapidly; the steamed sample remained unbleached for months. A product to withstand oxidation. The Bailey rancidity test2 is dependent upon autocatalysis treated sample, which, sealed in vacuo, had been kept in the and therefore gives values for susceptibility. It is, however, direct sunlight for 3 months, showed a negative Kreis test open to the objection that catalytic products are progressively after it had been stored at room temperatures for 3 years. A source of oxygen must be postulated to account for the removed during its operation. These products also affect the indicator used to determine the end point. The authors oxidation a t the double bond of the oleic acid at relatively have adopted the principle of measuring the length of the in- low temperatures. That it comes from the normal comduction period under more constant conditions, thereby ob- pounds is improbable. The oxidation of the unsteamed viating losses in the system. The apparatus now used in the sample may be explained by assuming that enough loosely laboratories of the Bureau of Dairy Industry is described in a combined oxygen to cause perceptible oxidation is present. The lack of oxidizing action in the steamed sample indicates publication already i ~ s u e d . ~ During experiments with butter oil certain irregularities a lack of free or loosely combined oxygen. An explanation in the curve within the induction heriod were noted. There of the mechanism of the reaction involved in the oxidation seemed to be a slight initial absorption some time before the in vacuo might perhaps be based upon the observations of a rapid absorption began. Closer study of this absorption number of investigators that hydrogen peroxide is found showed that a small amount of oxygen was actually taken up when oxidation occurs. The explanation of the formation by the fat, after which there was a comparatively short period of hydrogen peroxide assumes the formation of peroxides as the initial step in the reaction, subsequent formation of 1 Presented at the symposium on Cotton and Its Products, and Vegeactive oxygen, and the union of this oxygen with water. table Oils before the Division of Agricultural and Food Chemistry at the 71st Meeting of the American Chemical Society, Tulsa, Okla., April 5 to 9, It is evident that an interpketation of the foregoing observa1926. tions on milk fat, in the light of this theory, calls for a reaction I Cotton Oil Press, 7, 8,35 (1923). upon which data are too conflicting and too meager to sup8 Proc. World’s Dairy Congress, 2, 1253 (1923); J. Dairy Sci., 8, 515 (1925). 4
6
Tars JOURNAL, 17, 625 (1925).
6
Staudinger, Ber., W B , 1075 (1925). Greenbank and Holm, THIS JOURNAL, 16, 598 (1924).
