V O L U M E 2 2 , NO. 1, J A N U A R Y 1 9 5 0
191 4CK ?\io# L E D G M E N l
Comparative results obtained on gasolines by the microniethoti on 1-nil. samples and by the A.S.T.M. method requiring 130-ml.
samples are shown in Figure 5. The solid line is A.S.T.M. vapor pressure, located by points X ; the dots are microvalues and the numbers a t the dots represent the numbers of identical results obtained for the points shown, about half of them being repeats on one filling, and the rest individual tests on separate fillings. In practically every case the micro result is within 0.2 pound of the A.S.T.M. value. The standard deviation of the micromethod is 0.2 pound. This apparatus and technique can probably be adapted to eve11 smaller samples. The vapor pressure microprocedxe is useful in carburetor studies, test tube synthesis, stability studies, cstc. Xatelson ( 8 ) described an ingenious method for drterniining vapor pressure on a single drop of liquid. Vnfortunatrl>-, it is limited by its authors to pure substances and the present authors’ experience confirms its inapplicabi!ity to a mixture of hydrocsart)ons like gasoline. The present method is, of coursp. applic~ahlralso t o purr hydrowrhons in the ensnlinp range.
The authors express their appreciation to H. A. Mayen, E. J. Sklendr, and D. S. Stairs for their capable assi3tance in various phases of the experimental work, and to C. J. lnderson fnr his valuable aid in the preparation of the manuscript. LITERATURE CITED
(1) Ani SOC.Testing Materials, Designation D 97-39. 12) . , Zbid D 323-43. (3) . h o c . Offic. Agr. Chemists, “Official and Tentativr Methods of .Inalysis,” 4th ed., p. 408, 1935. (4) (‘annon, M.R.. and Fen3ke, M . R , IND. E ~ GCHEM., . ANAL.Eu., 10, 297 (1938). ( 5 ) Hain, G. M., .\m. SOC.Testing Materials, Bull. 147 (1947). (6) Kaufman, G., Finn, W. J., and Harrington. R. J., INn. F ~ o . CHEIC., A N A L . E D . , 11, 108 (1939). (7) Levin, I1 Ihid.,9; 147 (1937). (8) Natelson, S., and Zuckerman, J L.. I h i d . , 17, 739 (1945, RECEIVEDM a y l Y , 1949. Presented in [)art before the Division6 of .Inalyti-
.
cal and Micro Chemistry and Petroleurn Chemistry, Spniposium on Microchemistry and t h e Petroleum Industry, at the 115th l f w t i n g of t h P .AMERIC A T C H E \ I I C A L SOCIETY, 6an Franciaro. Calif.
Manometric Apparatus for Gas Measurements on Packaged Materials J. L. BLATT A y D PI’. P. TARASSUK Dairy Industry Division, University of Calijornia, Davis, Calif. \-RECEXT years, there has been an increasing interest in the
.relation of quality deterioration of various food and industrial products to the nature of t,he atmosphere surrounding the material during its processing or storage (1-5, 7-9). Some useful correlations have been made simply by the analysis of gases taken from containers before and after the material has been subjected to test conditions. However, in order to correlate certain quality changes with absolute gas pressures, or with milliliters (S.T.P.) of atmospheric gas per gram of packaged material, it is necessary also t o determine t,he effective volume and pressure of the confined atmosphere, and it is preferable, though usually not, possible with most equipment, to make all measurements in a continuous integrated procedure. Cartwright ( 3 ) has described a noteworthy apparatus xhich, in addition to permitting the determination of quality and quantity of gases about dry materials in all manner of containers, is adaptable to the detection of leakage in dry vacuumizcd packages, to the determination of gas permeabilities of packaging materials, to the determination of densities of dry irregular substances, and to the estimation of air entrapped in powders during manufacture. A portion of gas from a test container is transferred into a buret evacuated with a mechanical pump. The volume is read following compression under mercury to atmospheric pressure. By using a leveling bulb and manipulating three of the system’s five stopcocks, this gas is expelled and a similar fraction is introduced and measured. The original volume and pressure of gases in the container are derived from these values. The measurement of barometric pressure is determined separately. Samples of gas for analysis may be withdrawn from the container and transferred to an appropriat,e system. Fair reproducibility and accuracy are demonstrated when the packaged materials are essentially “dry” and relatively nondesorbing of gases during the procedure.
In the use of a simplified manometric apparatus the limitations of moisture and desorption inherent in Cartwright’s method are largely overcome, and distinct advantages in simplicity of construction and operation and precision in measurement are gained.
I n this procedure, the gas piessure and free space volume in a container are derived from the measurement of pressure when the volume of the container gases is expanded b?? t n o fixed amounts,
Tf rontainer ) P, = original gas pressure in the container Va = volume of one expansion Vb = volume of another expansion PI = pressure of gases after expansion into V.-Le., pressure a t volume VI = ( V , V5) P, = pressure of gases after expansion into Vb-i.e., pressure a t volume Vp = ( V , vb) and the temperature and the number of gas molecules measured remain constant, = an rinhiown volume (the effective free space in a
+ +
PzVz = K = PiVi = Pi(Vz
+
Vo)
PzVp = P*(V.z +
V b )
from which
or preferably
and Once the Pp/P1 ratio is found, graphs or tables may be constructed to eliminate the individual calculations of V , anti the pressure factor
(‘
z:
inasmuch as V , and Vb are constants.
Components which of necessity are common to both manomrtric and volumetric systems are a puncturing device, a means for clearing the system of contaminating gases before measurements are made, a measuring chamber into which containrr gases are expanded, a leveling system for the transfer and compression of gases, and a communicating pmsagi. to a gas analyzing system.
ANALYTICAL CHEMISTRY
192 These features have been met by a simple structure (illustrated in Figure 1) which combines a punch, P , a three-way 120” capillary bore stopcock, C, an expansion bulb, E, a 30-inch open Y manometer tube, M , an overflow trap, 0, a leveling bulb, L, and an adjustable scale, S, all mounted on a wood and metal supporting structure, D and F, such that most operations and observations are made a t eye level when one is standing. The glass components are relatively easily fashioned from stock Pyrex parts, the Y-tube from small-bore heavy-walled stock, and the leveling bulb, the overflow bulb, and expansion bulb from round-bottomed flasks. Translucent rubber is used for connecting passages El and Ez, which are made as short as practical. Scale S is a meter stick, calibrated in millimeters from bottom to top, and fitted immediately along side the left-hand manometer tube, so that it can be moved vertically through a distance sufficient to cover the range of local barometric pressures. It is held a t a desired position u-ith a wing nut and bolt. A sliding leveling bulb holder, H , allows the bulb to be adjusted to and held a t any desired height. The punch crank assembly, K , the sampling platform, A , the manometer board, D, the leveling bulb slide bar, 2, and other accessories are mounted to the pipe-supporting frame, F , by movable 90 O double-grip clamps, G. Permanent reference levels b and a are placed one above, the other below the level of bulb E, and the volumes enclosed between the surface of the container a t P and each of these levels in the chamber are calibrated-e.g., by using known container volumes. In the authors’ apparatus, these volumes (Vband V,) are 3.0 and 150.0 ml., respectively.
to manipulate stopcocks before making a second required reading but only to change the mercury level, measurement is concluded quickly and with a minimum of esposure of materials to altered pressures. The volume technique necessarily exposes material during the period of the first measurement to pressure changes of considerably greater magnitude and for longer duration. Elimination of Barometer Readings and Vapor Pressure Values in Calculations. Although the height of mercury sustained in an “evacuated” chamber is a function of both barometric pressure and the magnitude of saturated vapor pressure, nicaasurement of these values is eliminated in the scale setting
b \
COMPARATIVE FEATURES
Advantages in this apparatus arise from (1) features that could apply equally well to volume measurement techniques, and (2) those that result from measuring pressure rather than volume. Simplification of Stopcock System. The introduction and expelling of gases through a single three-way port a t the top of the measuring chamber not only facilitates the handling of gases with the leveling bulb, but (in reducing the number of stopcocks so needed from three to one) it simplifies construction and considerably lessens the maintenance needed to prevent leaks. Taking Measurements in a System Saturated with Water Vapor. By maintaining moisture on the walls of the measuring chamber, the behavior of water vapor in gas samples is changed from an unknown to a predictable and controllable factor. (If water is drawn into the measuring chamber and expelled, sufficient moisture remains on the walls to keep the chamber saturated with water vapor until cleaning is required.) In this technique, the contribution of water vapor to the total pressure is automatically deducted in the scale setting. (With the moist chamber evacuated, and the mercury in the chamber set a t reference level a, the zero of the adjustable scale is set opposite the mercury level in the left manometer tube. Thereafter, the “dry” pressure of gases held a t level a in the chamber can be read directly from the scale, regardless of whether gases in the container were moist or dry.) In volume measurements the barometric pressure used in calculations n-ould in each case be effectively reduced by a fixed amount-Le., by saturated vapor pressure. Elimination of Mechanical Pump. Instead of a mechanical pump, the leveling system can be used as a piston in clearing the measuring chamber and connecting passages of interfering gases by expelling them through E*. This double use of the leveling system not only eliminates the pump and its stopcock but allows the retention of moisture in the chamber. Replacing Volumetric Buret by Manometer Tubes and a Linear Scale. This simplifies construction and readings. AMeasureinents in this case are of length rather than volume; hence, many inexpensive scales, whose calibrations are easily and precisely checked, can be purchased, from which readings of threeand four-place figures can be made without the necessity of applying corrections. The readings themselves are made by bringing mercury to fixed levels in capillary tubing rather than by matching mercury columns of relatively large diameters. Reducing Inducement of Materials to “Desorb.” As it is necessary neither to remove gas from the measuring chamber nor
:i
J
Q 1 I 7
Figure 1. Apparatus
193
V O L U M E 2 2 , N O . 1, J A N U A R Y 1 9 5 0
to tlie analyzer buret, B , in the amounts needed. The relative pressure of gases in the chamber is immediately apparent from the manometer scale. When it is desirable to conserve test gas, the passageway to the buret, E?,may be cleared by displacement with mercury, obviating the need for rinsing or sweeping. By virtue of its simplicity, the apparatus is conveniently used as a sampling and transfer device, even when volume and pressure measurements are not required.
and does not enter into calculations. I n volume measurements, calculations must take into account the value of barometric pressure and the magnitude of saturated vapor pressure (or some value of vapor pressure) in addition to the value of atmospheric temperature utilized by both methods in converting figures to a common base. OPERATIOYAL PROCEDURE
Union of container A; with the measuring apparatus is made by moi.;tening the surface of the hollow rubber pad which surrounds punch P , and then compressing the pad by turning the pressure csrank, K , sufficiently to make a gas-tight bond. In evacuating the system with the leveling bulb, gases in E are first rvpelled through E*; thereafter, most of the gas in connecting passage E1 can be expanded into E and then expelled. Usually a single repetition of the procedure is sufficient for the “complete” evacuation, which is seen visually from the scale when the height of mercury sustained in the evacuated chamber by atmospheric pressure is the same for the Lvhole system as for chamber E alone. Leaks into the vacuumized system can be very quickly and critically detected (as evidenced by an ebbing mercury column) :n setting the mercury at mark b. After evacuating, a mer( ur \ seal can be left in passage E? as an added precaution against 1t.akage. The adjustable scale may be set for the atmospheric teniperature and pressure conditions peculiar to each determination. The container is punctured by further turning the pressure crank, K ; by using the leveling bulb the confining volume is successively extended to marks b and a,and the resultant pressures, P, and P I , are noted. For the pressure of gases held a t the upper mark, b, to avoid moving the scale, the vertical distance between marks a and b is subtracted from the corresponding direct scale reading. For convenience in reading, this distance is made to be an exact 100 mm.
ACCURACY
Representative calculations incorporating gas analysis data are illustrated in Table I1 for determinations made on a container of poxdered ice cream mix originally sealed in air, and another on nonfat dry milk solids originally sealed in an atmosphere of nitrogen. The figures given are particularly significant, not in regard to the quality of the materials and the packaging (as there are many variables not indicated), but as illustrative of the procedure and precision of results to be expected. The estimated probable error for each step in the determination is separately indicated for the first example. In quantities such as P I and Ppwhich are measured directly, errors given are determined largely by the specifications and calibration of equipment, and by the reproducibility of measurements. Estimations of the erior in calculated quantities, such as V,and P,, were derived by a method of partial differentiation (6) of the expressions from which these values were calculated and from the probable errors of the quantities measured dircctlv. In the example cited in Table 11, the partial errors in V, due to the probable errors in measurement of P2/Pl,Va and Vb were calculated as 1.9, 1.4, and 1.9 ml., respectively, the most probable error (indicated in the table) due to their combined effects being 3.1 ml. The sensitivities and accuracies indicated for the determinations of V,, P,, density, and the milliliters of gas in this method compare well with similar measurements made by other means, and might be improved in some cases by refinement in specifications and calibration. For example, from the expression for the derivation of V , i t is seen that the sensitivity of the determination is dependent on the structural specifications of the apparatus-
The reproducibility to be expected in readings, the validity of the scale setting, and the successful control of water vapor in
pressure mrasurements are demonstrated in Tablr I by the constancv of the sdveral P2/Plvalues obtained with different amounts cf moist gas in a systLm of fixed volume. Gas samples for analysis may be withdrawn from the container to any extent desired by using the leveling bulb and transferred
Trial
P2
PI
Ratio
Dev. from Mean
1 2 3
754.0 711.0 607.0 540.0 491.0
482.0 454.0 389.0 345.0 314.0
1,5643 1.5661 1.5604 1 ,5650 1,56863 1.5639
0.0004 0,0022 0.0035 0.0011 0.0003
?
Table 11.
Mean
+ Va +
0,0015
Representative Determinations Illustrating Calculations and Precision of Measurement
Determination Pressure a n d free apace
Quantity
Pr
PI PdPI Vs
PZ Apparent densityb
Temprraturn of measurements Haldane analysis
TVm (wt. of material) I’, ( v o l . of container) V m (id.of material) Apparent density T O
CO2 0 2
Partial pressure a t 0’ C.
coz 0 2
Gas. mi. (S.T.P.) per gram of material
COz
Derivation hleas. Meas. Calcd. I’a - Vb X ( P ~ ’ P I ) ” PdP1 1 PI(VZ Th) V. Meas. Meas. I’c - Vz TVm 1 I’m hIra9. Meas. Meas. % COz X Pr X 273 100 (2’ 273) % Oz X Pz X 273 100 ( T 273)
+ -
0 2
V O (calibrated) = 158.0 * 0.5 ml. vb (calibrated) = 3.0 * 0.5 ml.
+ + Pcoz
x ___1’s
760 X W m
V2 a
V
which determines the ratio of P,/P1. Vz Vb With the limitations indicated for the chamber volume calibrations and for the reproducibility of pressure readings, the capacity of bulb E needs to be approximately 10% or more of the volume of V,, and the passageway volume E1 kept small to get full accuracy from the apparatus.
Le., on the size of
Table I. Reproducibility of P2/Pl Ratio with Varying Amounts of Moist Gas in System of Fixed Volume
x
Po2
760 X W’m
Example 1 (Ice Cream Mix) 694.0 mm. 513.0 mm. 1.353 422 ml.
Probable Error tO.5
*0.5 =0.0016 13.1
Example 2 (Milk Powder)
733 .O mm. 470.0 mm. 1,560 265 ml.
699 mm.
11.6
741 m m .
454 grams 835 ml. 413 ml. 1.10 25.6’’ C. 2.04% 9.71% 1 3 , 0 mm,
13.0
=0.32
241 gram9 4.52 ml. 187 ml. 1.29 28 20 1.14% 0.11% 7.78 mm.
62,0 mm,
10.35
0.75 mm.
0.0159 &./gram
t0.0004
0.0112 ml./gram
0,0758ml./gram
+0.0009
0.0011 d . / g r s m
+6.0 16.8 =0.01s
-0.2 10.05 10.05
c.
b Designates density of milk solids together with air cells entrapped in powder during manufacture, as contrasted with “cell-free” density.
ANALYTICAL CHEMISTRY
194 LITERATURE CITED (1) Boggs, M. M.,and Fevold, H. L., Ind. Eng. Chem., 38, 1075-9 (1946). (2) Boyd, J. M., and Peterson, G. T., Ibid., 37,370-3 (1945). (3) Cartwight, c*v I N D . E N G * C H E M . ? h - 4 E~D . , 18, 779-85 (1946). (4) Coulter, S. T., and Jenness, R., Univ. Minn., Agr. Expt. Sta., Tech. Bull. 167 (1945). (5) Dunlop, A. P., Stout‘,P. R . , and Swadesh,S., Ind. Eng. Chem., 38, 705-8 (1946).
(6) Franklin, W. S., “Precision of Measurernent,” pp. 6-10, Lancaster, Pa., Lancaster Press, 1925. (7) Lea, C. H., Moran, T., and Smith, J. A . B., J . Dairy Research, 13, 162-215 (1943). ( 8 ) Stadtman, E. R., Barker, H. 9..Haas, V., Mrak, E. M., and MacKinney, G., Ind. Eng. Chem.,38,3324 (1946). (9) Tarassuk, N. P., FoodInds., 19,781-3 (1947).
RECEIVED November 19, 1947.
Determination of Phosphorus in Iron Ore JAMES L. KASSNER AND MARY ALICE OZIER University of Alabama, Uniuersity, Ala.
HE determination of phosphorus in iron ore is carried out in Tthree steps : solution of the sample, precipitation of the ammonium molybdiphosphate ( 7 ) , and alkalimetric titration of this salt to determine the amount of phosphorus present. This study deals specifically n-ith the second and third steps in this procedure. The solution of the sample is effected by standard procedure. The single-strength citromolybdate solution used in the determination of phosphorus pentoxide in phosphate rock ( 3 ) did not give complete precipitation when used in the determination of phosphorus in iron ore. After considerable experimentation a double-strength citromolybdate solution was prepared and found to be stable. This study has shown that the time required for a complete determination of phosphorus in iron ore can be shortened by using the new double-strength citromolybdate solution and separating the .ammonium molybdiphosphate a t the boiling point. The analysis of several Bureau of Standards samples indicates that the precision and accuracy of the method are good. The new mixed indicator (3)used in the determination of phosphorus pentoxide in phosphate rock is used in determining the end point. REAGENTS AND STANDARD SOLUTIONS
Double-Strength Citromolybdate Solution. Solution A . Dissolve the following reagents in 1400 ml. of water and warm while stirring until solution is complete: 100 grams of ammonium nitrate, 128 grams of citric acid monohydrate, and 136 grams of ammonium molybdate, ( T ~ ” ~ ) & ~ O , O N . ~ H ~ O . Solution B. Dilute 528 ml. of concentrated nitric acid (specific gravity 1.42) with 300 ml. of water. Prepare the citromolybdate solution by pouring Solution A into Solution B. Clear i t as follows: Add 10 to 15 drops of 20Q/,diammonium hydrogen phosphate solution, boil 5 to 10 minutes, allow to stand overnight; then siphon off the clear solution. (Such a solution remained clear 2 years.) The other reagents for this method are essentially those used in the determination of phosphorus pentoxide in phosphate rock
Wash the precipitate with hot water, dissolve in not more than 20 ml. of hot 1 to 2 nitric acid solution, and add it to the reserved filtrate. Dilute the solution to 80 ml., add 100 ml. of double-strength citromolybdate solution, heat to boiling, and keep a t this temperature for 5 to 10 minutes. Remove the solution from the heat and filter immediately. Before transferring the precipitate to a Gooch crucible, wash it three times by decantation with 1% nitric acid solution, using about 5 ml. for each wash. Transfer the precipitate to the crucible and wash it 10 to 12 times with 1% potassium nitrate solution. Place the crucible in the original beaker and dissolve the precipitate in a known volume of 0.1 N sodium hydroxide solution, using about 30 ml. in excess (3). Add 0.5 ml. of the mixed indicator (S) and titrate the solution with 0.1 X nitric acid until it turns yellow. Remove the crucible from the beaker, wash with carbon dioxide-free water, and adjust the volume to about 100 ml. In direct sunlight or in front of an illuminator equipped with a fluorescent daylight Xlazda lamp, back-titrate the solution with 0.1 ,V sodium hydroxide until a purple coloration appears and remains. The percentage of phosphorus is calculated on the basis of: 1 P == 23 NaOH. Data are tabulated in Table I. DISCUSSION AND N O l E S ON PROCEDURE
Arsenic seems to interfere more in this procedure than it does when the precipitation is carried out a t a lower temperature by shaking. If arsenic is present, i t should be removed as rerommended by Lundell, Hoffman, and Bright (6). Table I. Sample No.
Results Obtained with Bureau of Standards Iron Ores Interferences Present Ti02
% 26
vios
7,
0.07
P206
.
Exptl. Value
%
%
0.04
0.115 0 loa 0:10; 0.09
+o,
0.1oc
+O.Ol
0.09c
(5).
27B
0.023
0.004d
0,036-
29
0.99
0.08
1.01
PROCEDURE
Weigh out a 2-gram sample of iron ore into a 150-ml. beaker, add 20 ml. of concentrated hydrochloric acid (specific gravity 1.19) ( 8 ) ,heat the covered solution on a hot plate unOil the ore is dissolved, add 5 to 10 ml. of concentrated nitric acid (specific gravity 1.42) ( 4 ) , add 12 to 15 ml. of 60 to 70y0perchloric acid ( 1 , 2, 11, lb), heat on a hot plate to copious fumes of perchloric acid, and fume a t least 5 minutes to dehydrate the silica. Wash the filter with hot 1%nitric acid solution and then with hot water. Reserve the filtrate. In order to recover any phosphorus that might be retained in the residue, volatilize the silica by treating the residue with an excess of hydrofluoric acid and a small amount of nitric acid (6); fuse the residue with sodium carbonate, leach with warm water, and filter to remove any titanium that might be present. Add to the filtrate from the fusion a little ferric chloride free from phosphorus and precipitate the ferric phosphate with ammonia (IO).
Pro5
Certified Value
Deviatior, 02
+o.oi
f0.01 0.00
0.00
0.03Cia 0 035‘ 0:031! 0.036 0.037c 0.035c
-0.001 -0.001 -0.005 0.000 +0.001 -0.001
1.0Cia
fO.04
1.04a 1.05b 1.04b 1.03c 1.01c
f0.03 f0.04 +0.03 +0.02 +0.03
10 minutes a n d allowed t o stand overnipht before filterinn. * Boiled Boiled 10 minutes and filtered immediately. Boiled 5 minutes a n d filtered imrnediatelp.
a
d e
Per cent vanadium. Per cent phosphorus.
