SEPTEMBER 1.5, 1936
ANALYTICAL EDITION
conversion of basic nitrate into phosphate was followed by testing the precipitate for nitrate ion, indicated the desirability of digesting the precipitate for an hour before filtering. Series 8 and 9 indicate but little error from occlusion of potassium and sodium and the feasibility of precipitating with phosphate of potassium or sodium rather than ammonium.
Separation of Bismuth from Other Ions The slight solubility of bismuth phosphate in dilute nitric acid suggests the possibility of separating it from a number of metals with which it is frequently associated. Table I1 gives experiments with 50-cc. portions of the standard bismuth solution, in the presence of certain nitrates. TABLE11. WEIGHTOF BISMUTH PHOSPHATE
a
(Found by the standard procedure in the presence of other ions) Added'" BiPOd Found Gram 0 . 3 3 2 4 and 0.3317 Mg(N0s)t 0.3311 and 0 . 3 3 2 3 Zn(Nod z 0 . 3 3 5 3 and 0.3368 Cd(N0dz 0 . 3 3 2 3 and 0 . 3 3 2 4 Cu(N0s)z 0 . 3 3 2 6 and 0 . 3 3 4 1 Ca(NOs)z 0 , 3 7 7 0 and 0 . 3 8 8 1 Pb (N0s)z 1 gram in each case.
Obviously the separation of bismuth from magnesium, zinc, copper, and calcium by this process offers no difficulty.
353
The separation from cadmium gives a slight error, probably due to occlusion, and separation from lead, a t least under the conditions here suggested, is not possible.
Summary of Results Bismuth can be accurately determined as the phosphate, if separated from solutions which contain neither C1- nor SO1-- and are approximately 0.2 M as to nitric acid and approximately 0.065 M as to soluble phosphate. The method is accurate in the presence of moderate concentrations of Nai, Kf, Mg++, Zn++, CU++,and Ca++, gives slightly high results in the presence of Cd++, but is not accurate in the presence of Pb++. The chief source of error is the co-precipitation of basic salts; this can be avoided, in the presence of sufficient H+, by precipitating from a hot solution with a hot dilute phosphate solution and digesting for an hour a t 80" C. A second possible source of error is the occlusion of small amounts of ammonium phosphate; this can be eliminated by avoiding large concentrations of soluble phosphate, and by igniting the precipitate to 800" C. before weighing.
Literature Cited (1) Schoeller and Waterhouse, Analyst, 45, 436 (1920).
RECEIVED June 16, 1936
c
Microdetermination of Carbon and Hydrogen In Compounds Containing Arsenic, Antimony, Tin, Bismuth, and Phosphorus F. C. SILBERT A~%DW. R. KIRNER, Coal Research Laboratory, Carnegie Institute of Technology, Pittsburgh, Pa.
D
IFFICULTIES have been reported in the literature on the determination of carbon and hydrogen in compounds containing arsenic (IO),antimony (9),tin ( 6 ) ,bismuth ( 7 ) ,and phosphorus (1, 2, 3, 6, 8). In some cases these difficulties can be successfully overcome by the addition of suitable materials-. g., lead chromate, red lead, or copper oxide -to the combustion tube filling and to the sample in the boat. In certain cases these, and other subterfuges, fail and some investigators have determined the carbon only by a wet-combustion method. In many cases no attempt is made to determine either carbon or hydrogen, only the percentage of the metallic element present being determined. In connection with a study of the exhaustive chlorination of coal conducted in this laboratory, samples which contained appreciable quantities of antimony or phosphorus were submitted for analysis. Since a knowledge of the distribution of the elements of the coal among the reaction products was required in this work, it was important that the carbon-hydrogen content of the samples be known with some degree of accuracy. When the antimony-containing samples were analyzed for carbon and hydrogen by the ordinary microprocedure using a Pregl Universal tube filling, considerable amounts of a white crystalline substance (antimony oxide) condensed in the constricted end of the combustion tube and in the capillary and forechamber of the Dehydrite-filled absorption tube, which, of course, produced an error in the hydrogen determination. Further, a carbon-hydrogen determination on a pure, known compound made directly following such an analysis yielded erroneous results. In the case of the phosphorus-containing sample tlhere was no visible difficulty, but again a directly succeeding analysis on a pure, known
compound yielded false results, so that no confidence could be placed in the analysis of the phosphorus compound. Of the methods mentioned in the literature, the modified Dennstedt method recommended by Falkov and Raiziss (4), for the macrodetermination of carbon and hydrogen in organic arsenicals and mercurials, seemed most likely to succeed when applied to compounds containing antimony and phosphorus. It was found that a modification of their method could be successfully adapted to the microanalysis of such compounds. The micromethod was first tested on a pure, known organic arsenic compound and the results of Falkov and Raiziss were confirmed. The method was then extended to pure, known compounds containing, respectively, antimony, tin, phosphorus, and bismuth, and was finally applied to the abovementioned coal samples.
Experimental The analytical samples, unless otherwise designated, were pure compounds obtained from Eastman. The phosphorus and bismuth compounds were recrystallized from methyl. alcohol, the arsenic and antimony compounds from ethyl alcohol, and the tin compound from ether. Instead of using a Dennstedt catalytic combustion on platinum as recommended by Falkov and Raiziss, a portion of the copper oxide-lead chromate filling of an ordinary Pregl Universal filled combustion tube was removed and replaced by a 3-cm. cylinder made of 200-mesh platinum wire gauze filled with granulated red,lead and a 1-cm. plug made of platinum wire gauze. The red lead was prepared by igniting Merck's lead peroxide ( p r o analysi, granuliert nach Pregl), in a stream of oxygen in a microcombustion tube in an electric combustion furnace at the normal combustion temperature. To prevent any red lead dust from sifting
INDUSTRIAL AND ENGINEERING CHEMISTRY
354
VOL. 8, NO. 5
TABLEI. RESULTS OF ANALYSIS Sample
Substance
NO.
1
2
3
4
CisHisAs Triphenylarsine
Weight of Sample
-H D
Found
H
C
H
C
%
%
%
%
70.50 70.76
-0.12 +0.07 ___ -0.07 -0.04 -0.10 +O. 05 +O. 08
-0.08
,Mg.
,Mg.
1Mg.
3.524 3.616 4.619
1.517 1.619 2,011
9,109 9.382 11.940
4.530 2.932 3.666 5.533 3,580 2.920 3.677 4.573 3.920
1.517 0.933 1.206 1,726 1.181 0.955 1.188 1,523 1.282
3,934 4.119 3.987 4,678 5.081 3.108 3.517 3.570
0.540 0.657 0.657 0.700 0.847 0.441 0.517 0,532
4.82 5.01 4 2 Mean = 4.90 6.965 4.19 6.842 4.34 10.640 4.37 9.301 4.35 12.210 4.39 9.284 4.29 Mean = 4.32 8.437 3.75 5.472 3.56 6.855 3.68 10.360 3.49 6.675 3.69 5.471 3.66 6.875 3.62 8.493 3.73 7.298 Mean = 3.65 3.183 1.54 3.356 1.78 3.204 1.56 3.745 1.67 4.085 1.87 2.509 1 59 2.826 1.65 2.865 1 67
Triphenylphospbine
4,280 3.511 3.560
2.245 1.820 1.848
12.950 10.604 10.770
CasHir OiP Tri-o-phenylphenyl phosphate
3.531 3.473
1.579 1.546
Triphenylthiophosphate
Ci!HisOsSP
3.291 4.275 3.553
1.324 1.734 1.374
Triphenylbismuthine
CiqHisBi
3,804 3.674
1,257 1.176
ClsHlsClzBi Triphenylbismuthine dichloride
4,372 5,756 5.191
1.196 1,567 1.430
Ci?HlsClSn, Triphenyltin chloride
3.527 3.521
1.261 1.291
CiaHisSb Triphenylstibine
Ci8HiaCIzSb Triphenylstibinic chloride5
CeHsOsNClSb 2-Chloro-5-nitrophenylstibonicacid6
3.107 3,054 4.708 4.152 5.443 4.142
1.164 1.185 1.838 1.614 2.137 1.588
Mean =
5
10
6
CiqHiaP
Difference from Theory
coz
1.87
5.87 5.80 5.81 Mean = 5.83 10.097 5.00 9.920 4.98 Mean = 4.99 7.626 4.50 9.915 4.64 8.240 4.33 Mean = 4.46 6.866 3.70 6.627 3 . 5 8 Mean = 3.64 .-. 6.730 3 06 8.876 3 05 8.049 3 .08 Mean 3.06 7.275 4.00 7.251 4 2 Mean = 4.05
-
70.50
70.59 61.14 61.11 61.06 61.10 61.18 61.13 61.12 50.80 60.90 51.00 51.07 50.85 51.10 50.99 50.65 50.77 __ 50.90 22.07 22.22 21.92 21.83 21.93 22.02 21.91 21.89 21.97 82.52 82.37 ~
f0.06
+O.lO 0.00 __
+ O . 03 $0.18 -0.01 $0.11
-0.08
+0.12 $0. 09 + O . 05 $0.16 $0.09 $0.08 0.00 +0.24 $0.02 $0.13 +0.33 $0.05 $0.11 $ 0 , 13 10.13 $0.10 $0.03
e 82.47
+0.04
77.99
$0.09
$0 08
77.90 77.95
+0.07
63 20 63 25 83.25 63.23 49.23
$0 08 +0.12 -0 09 +O 04 +0.26 f0.14 +o. 20 +O.lO +O 09
49.19 49.21 41.98 42.06
+0.08
42.29 42.11
+0.12
56.25
4-0.08
56.16
56.21
+O.lO
+o.ls $0.13
$0.18
-0.08 $0.01 -0.07 -0.10 -0.15 -0.11 -0.03 -0 08 -0.09 -0.17 -0.07 +0.03 +o. 10 -0.12 $0.13 $ 0 , 02 -0,32 -0.20 -0.07 $0.14 SO.29 -0.01 -0.10 0.00
+0.09
-0.02 -0.04 +0.04 +0.12 -0.03
+o.ll
$0.07 +0.04 __ -0.05 0.00 $0.08 +O 13
+O.ll +0.15 +0.11 C0.13 -0.29 -0.21
Metal
% 24.48As 24.48As 24.48AS 34.51 Sb 34.51 Sb 34.51Sb 34.51Sb 34.51Sb 34.51Sb 28.73Sb 28.73Sb 28.73Sb 28.73Sb 28.73 Sb 28.73Sb 28.73Sb 28.73Sb 28.73Sb 37.09 Sb 37.09Sb 37.09Sb 37.09 Sb 37.09Sb 37.09Sb 37.09Sb 37.09 Sb 11.83P 11.83P 11.83P 5.60P 5.60P 9.07 9.07P 9.07P 47.49Bi 47.49Bi
$0.02
40.90Bi 40.90Bi 40.90 Bi
+o.lo
30.81 Sn 30.81Sn
-0.16 $0.19
1-0.15
Prepared in this laboratory by J. F. Weiler. of C. S. Hamilton of the University of Nebraska.
b Kindly supplied through the courtesy
through the platinum gauze, a thin layer of asbestos lined the entire inner surface of the cylinder, including the ends. This snug-fitting cylinder ensured more intimate contact of the combustion gases with the red lead than if the latter was merely placed in a boat, as recommended by Falkov and Raiziss. The details of the filling are illustrated in Figure 1. The samples miere burned by the usual procedure, the water formed being absorbed on Dehydrite and the carbon dioxide on Ascarite. In the case of the phosphorus compounds a carbonaceous deposit formed on the inner surface of the cornbustion tube just adjacent to where it entered the electric combustion furnace; in order to remove this carbon quanti-
FIGURE 1. COMBUSTION TUBEFILLING
tatively the combustion tube had to be strongly heated on all sides with a bare Bunsen flame. The antimony, bismuth, and tin compounds left a white deposit (antimony, bismuth, and tin oxides) on the inner surface of the combustion tube which could not be removed even on strong heating. In the case of the antimony compounds especially, it was observed that some
of the compound distilled into the portion of the combustion tube surrounded by the heated furnace while a portion remained outside; the latter, on being subjected to the heat from the Bunsen burner, decomposed leaving a residue on the inner glass surface. That material which distilled into the combustion tube suffered thermal decomposition and the antimony oxide Was &sorbed by the PlatinUm-red lead filling, apparently forming lead antimonate. In no case, when using this filling, Was any deposit of crystalline material observed in the constricted end of the combustion tube or in the capillary or forechamber of the water-absorption tube. After a number of such antimony-containing samples had been burned it was noticed that the platinum acquired a definite bluish iridescence and the surface of the red lead granules was coated with a yellow incrustation. After analysis of some of the other compounds, the red lead was also partially covered with a grayish metallic looking coating.
Results The results of the analysis of these compounds are summarized in Table I. The carbon-hydrogen values on the arsenic, antimony, and phosphorus compounds are accurate to about 0.1 per cent and the bismuth and tin compounds to about 0.2 per cent. Calculation of the observed and theoretical carbon-hydrogen
ANALYTICAL EDITION
SEPTEMBER 15, 1936
ratios for all these substances revealed that, if this observed ratio (for the CIS compounds) was not in error by more than about 3 per cent, the correct number of hydrogen atoms were obtained by calculation, assuming the theoretical number of carbon atoms to be present. With errors greater than 3 per cent, however, the number of hydrogen atoms calculated would be in error by one unit; such was the case for samples 8 and 9. I n the case of the Cg compound the error in the carbon-hydrogen ratio can be three times larger without making the error in the calculation of the number of hydrogen atoms any greater.
Summary 1. The determination of carbon and hydrogen in compounds containing arsenic, antimony, tin, phosphor'-% and bismuth using the ordinary Liebig or Pregl procedure is extremely difficult or even impossible. 2* By a modification Of the Fakov-Raiziss macromethod, the microdetermination of carbon and hydrogen in the above compounds can be successfully performed. The important
355
feature of the method consists in the introduction of a layer of platinum gauze and of red lead as an integral part of the combustion tube filling to remove metallic oxides which otherwise vitiate the results. 3. The results on the arsenic, antimony, and phosphorus compounds are accurate to about 0.1 per cent and on the bismuth and tin compounds to about 0.2 per cent.
Literature Cited (1) Dennatedt, M., 2. phvsiol. Chem., 52, 181-3 (1907). (2) Erlandsen, A., Ihid., 51, 86 (1907). (3) Evans, P., and Tilt, J., Am. Chem. J . , 44, 364 (1910). (4) Falkov, M., and Raiziss, G., J . Am. Chem. Soc., 45, 998-1003 (1923). (5) Hilpert, S., Ber., 46, 951 (1913). (6) Krause, E., and Schmitz, M., Ihid., 52,2156 (1919). (7) Marquardt, A., Ihid., 20,1518 (1887). ( 8 ) Messinger, J., Ihid., 21, 2910 (1888). (9) Rosenheim, A,, and Loewenstamm, W., Ihid., 35, 1124 (1902). (10) Steinkopf, W., and Mailer, J,,I h i d , , 54, 845 (1921). RECEIVED June 20, 1936.
Determination of Neutral Equivalents of Higher Fatty Acids R. B. SANDIN, M. KULKA,
AND
D. W. WOOLLEY,' University of Alberta, Edmonton, Alberta, Canada
IK
CONNECTIOK with studies of certain binary systems of the higher fatty acids and with studies of synthetic fats (6),it was felt that improvements might be made in the ordinary method for determining the neutral equivalent of a higher fatty acid. The customary procedure is to dissolve a given weight of the fatty acid in enough alcohol, neutral to phenolphthalein, to make the alcohol content a t least 50 per cent a t the end of the titration. The alcoholic solution is then titrated with aqueous alkali, phenolphthalein being the indicator. The authors have found through considerable experience that, in spite of the apparent simplicity of the procedure, to get reproducible and accurate results requires considerable skill. Bishop, Kittredge, and Hildebrand ( I ) have called attention to the fact that the use of alcohol as a solvent in acidbase titrations may be advantageous for two reasons: Its solvent power for certain substances, such as the fatty acids, which are not soluble in water; and the somewhat greater sharpness of the end points obtainable (3). With this view in mind, Hildebrand and eo-workers ( I ) have prepared an indicator scale for alcoholic solutions similar to those in common use for aqueous solutions. They have shown that palmitic acid, for example, is neutralized by sodium ethylate a t about 0.8 volt, so that thymolphthalein should change color close to the true end point. Kolthoff and Furman (4) have also pointed out that alcohol lowers the dissociation constants of both weak acids and indicators. I n addition, the ion product of water is much smaller with increasing alcohol content. The method for determining the neutral equivalent of a fatty acid of high molecular weight, described in this paper, involves titrating the acid in absolute alcohol solution, with sodium ethylate as the base, using thymolphthalein as the indicator, as suggested by Hildebrand. The advantage of a two-color indicator is obvious, and a combination of methyl orange and thymolphthalein has been found to be a distinct advantage. The color change is from yellow to green and is very readily detected. To make the end point even more 1
Present address, 1717 University Ave., Madison, Wis.
readily determined, the titration is performed in a Nessler tube. Finally, the primary acid standard, which has been found to be very satisfactory, is a highly purified grade of stearic acid.
Reagents and Apparatus The purification of the alcohol and the preparation of the sodium ethylate (0.05 N ) were carried out according to Bishop, Kittredge, and Hildebrand (1). The sodium ethylate was stored in a flask under an atmosphere of purified hydrogen furnished by a Kipp generator. The sodium ethylate solution was delivered to a 10-cc. buret, divided into 0.05 cc., attached t o the flask in such a way that the solution was forced over by the hydrogen pressure. By maintaining a constant positive pressure of hydrogen in the main reservoir, the ethylate solution could be kept colorless for several weeks at a time. The titration was performed in a 50-cc. Nessler tube (about 16 cm. internal diameter) set in a wooden rack finished in dull black and fitted with an opal glass reflector set a t an angle at the bottom. Stirring could be carried out by bubbling tank nitrogen through the solution, or, because of the small area of solution exposed to the air, with a ring stirrer made from glass rodding. The sodium ethylate was standardized against pure stearic acid. To obtain a stearic acid sufficiently pure for this purpose, Eastman Kodak Company stearic acid of melting point 69" t o 70" C. was crystallized from acetone until a constant capillary melting point of 69.6" t o 69.8" C. (6) was obtained. It was then dried in oacw, over sulfuric acid in an Abderhalden drier (9) and at the temperature of boiling water. The remaining fatty acids used in the experimental work were Eastman products, purified by repeated crystallization from acetone and dried in the same way as the stearic acid. The palmitic acid had a melting point of 62.4" to 62.7' C., myristic acid 54.4' t o 54.8" C., and lauric acid 44.1" t o 44.3" C. The thymolphthalein indicator solution was made by dissolving 0.5 gram of the indicator in 100 CC. of alcohol, The methyl orange solution was made by dissolving 0.2 gram of the dye in 1 liter of water.
Procedure Weigh into a Nessler tube not over 0.15 gram (a quantity which will require from 9 t o 10 cc. of 0.05 N sodium ethylate solution) of the fatty acid. Add 10 cc. of the purified alcohol, taking care to wash down any particles of fatty acid clinging to the walls of the tube. Add 5 drops of thymolphthalein indicator and 3
