I N D U S T R I A L A N D ENGINEERING CHEMIXTRY
860
Vol. 20, No. 8
been fairly generally accepted as standard-that is, where all substances involved are a t the standard pressure (more strictly, fugacity) of 1 atmosphere. To take a particular case, consider the reaction
range considered (0” to 400” (3.). Table I in that paper clearly shows that the temperature coefficients of the different reactions are different. A relation between the equilibrium constants of the different reactions, which holds for one temperature range, may not hold for another. 2CO 5Hz = CiHe 2H20. I n conclusion, a few minor errors in Francis’ paper3 should be pointed out. It is inconsistent to use the present writer’s value for the free energy of ethane, which was derived from represents the maximum work obtainable (free-energy in- his value for methane, unless the tatter value is accepted. crease) in the reversible formation of 1 mol of CzHG at a pres- This, however, makes an error of but about 500 calories, sure of 1 atmosphere when each of the substances involved which, in comparison with the reliability of some of the other is maintained at the beginning and throughout the process data used, is perhaps not important. a t a constant pressure of 1 atmosphere. This free-energy Francis3 erroneously compares his value for methane increase is then a measure of the tendency for this reaction to (gas, 1 atmosphere) with Parks and Kelley’s value for take place. It is true that in practice a process such as this methane (liquid, 1 atmosphere) which was derived from in which the pressures of all the substances involved are Lewis and Randall’s6 value for methane (gas, 1 atmosphere). 1 atmosphere a t the beginning and throughout the process The vapor pressure of (hypothetical) liquid methane a t would never be encountered. But this, nevertheless, is the 25” C. and 1 atmosphere would, of course, not be 1 atprocess the writer has chosen to consider as a standard for mosphere. Francis’ statement that “practical pressures will comparison, and this is the general practice in thermo- not usually overcome an unfavorable free-energy change of dynamic considerations. Thus, when the value of the con- more than 5000 calories” is rather loose. The effect of presstant of the reaction, K , is larger, the thermodynamic teiid- sure depends upon the magnitude of the decrease in volume ency for the reaction to take place is greater. And, although accompanying the reaction. As a matter of fact, the synin forming a mol of one hydrocarbon the molal proportions thesis of methanol from carbon monoxide and hydrogen is of reactants and resultants required are different from those carried on a t temperatures where the free energy increase at required for another hydrocarbon, all the free-energy quan- standard pressure is over 9000 calorie^.^ It must be admitted tities that have been compared refer to the formation of 1 -and this is a criticism that applies to certain of the writer’s mol of hydrocarbon from the same reactants and resultants own calculations as well 8s to those of Francis-that, as has a t the same partial pressure. The actual processes corre- been shown frequently in the past and as will be shown sponding to given free-energy changes are set forth especially again in a paper soon to appear from this laboratory, freeclearly by Noyes and SherrX5 energy values calculated on the basis of rough approximaThe statement in the first conclusion of the writer’s paper2 tions to and extrapolations of thermal data are often quite concerning the relative tendencies for different hydrocarbons erroneous. to form from water gas, of course, refers to the temperature 6 “Thermodynamics,” McGraw-Hill Book Co., New York, 1923.
+
6
+
“Chemical Principles,” The Macmillan Co , New York, 1922.
7
Lewis and Frolich, IND.END.CHEX.,20, 285 (1928).
Use of Buffers in the Determination of Color b y Means of Titanium Trichloride’ I-Amaranth, Ponceau 3R, and Orange I 0. L. Evenson and D. T, McCutchen COLOR CERTIFICATION LABORATORY, FOOD,DRUG,AND INSECTICIDE ADMINISTRATION, DEPARTMENT OF AGRICULTURE, WASHINGTON. D
HE original method for the evaluation of color in azo dyes by means of titanium trichloride was formulated by Knecht and HibberL2 The hot-water solution of the dye was reduced in the presence of hydrochloric acid, Rochelle salts, or sodium bitartrate, in an atmosphere of carbon dioxide. For some time this laboratory has carried out the titration of Amaranth (Colour Index 184) in the presence of hydrochloric acid. This method was found objectionable, however, for three reasons: (1) The end point is not sharp; (2) results tend to be slightly low, owing, in small part rtt least, to fading of the dye in acid solution; (3) it does not permit accurate or convenient evaluation of total color in mixtures of Amaranth with other dyes which cannot, or can only with difliculty, be titrated in acid solution. In an attempt to obviate the necessity of using acid, the titration of Amaranth in the presence of various buffers (or catalyst-buffers) was
T
Presented before the Division of Dye Chemistry at the 75th Meeting of the American Chemical Society, St. Louis, Mo., April 16 to 19, 1928. 4 “New Reduction Methods in Volumetric Analysis,” Longmans, Green and Co., New York, 1918. 1
c.
investigated. On obtaining good results in these determinations, the experiments were extended to other dyes. Materials
Commercial samples of dye of certified grade were used, the analysis being made according to the methods prescribed for color ~ertification.~ The following salts were tried as buffers: Rochelle salt, sodium bitartrate, calcium carbonate, sodium acetate, sodium tartrate, sodium citrate, potassium antimony tartrate, and sodium bicarbonate. These were of commercial c . P. grade as obtained from several sources. The 0.1 N titanium trichloride used was standardized with a ferric sulfate solution made from pure ingot iron.a This result was checked by standardization against sodium ~ x a l a t e . ~The titanium solution was 1.4 N with respect to the hydrochloric acid present. Procedure
The buffer salt, in the quantity to be used, was dissolved in water by heating to boiling in a wide-mouth Erlenmeyer 8
U. S. Dept. Agr., Bull. 1390, revised (1928).
INDUSTRJAL A N D ENGINEERING CHEMISTRY
August, 1928
or sodium bicarbonate the results of titration checked closely the theoretical and were consistent under varying conditions, Titration of Orange I (Colour Index 150) gave good results in the presence of all the buffers tried, except potassium antimony tartrate, calcium carbonate, and sodium acetate. The complete analyses of samples of these dyes are shown in Table 11. The “color by difference” agrees very closely with that obtained by titration in the presence of the buffer salts indicated. Crocein Orange (C. I. 26), Orange G (C. I. 27), Ponceau 2G (C. I. 28), Scarlet GR (C. I. 78), and Ponceau 2R (C. I. 79) gave low results with sodium bitartrate. New coccin (C. I. 185), which is isomeric with Amaranth, does not give low results with this buffer, it being possible to titrate this dye accurately in the presence of sodium bitartrate.
flask. The dye solution was then added and the contents of the flask again brought to boiling. The total volume in the flask was in all cases 100 cc. when titration was begun. While the titration mixture was kept in an atmosphere of carbon dioxide, the reducing solution was introduced a t such speed as it reacted with the dye until near the end, then drop by drop to end point. During the addition of the titanium trichloride the flask was continuously shaken, Results
Before any value can be placed on the results of a volumetric determination for color, they must be consistent for varying concentrations of dye in the flask and for different quantities of buffer; they must also agree closely with the “color by difference” wherever complete analysis can be made. The titration values for Amaranth when determined in the presence of Rochelle salts, sodium bitartrate, or sodium tartrate were very erratic. (Table I) The results obtained using calcium carbonate or sodium acetate as the buffer were not consistent for the two dye concentrations. The results using sodium citrate, potassium antimony tartrate, or sodium bicarbonate were consistent and accurate for any dye concentration used in flask. The end point in each case is very sharp. Table I-TiCt
Determination of Possible Errors
To determine the necessity for making a correction for titanous chloride consumed by the buffer, sodium citrate or sodium bicarbonate in different quantities was added to a standard solution of ferric ~ u l f a t e . ~No increase in the quantity of reducing solutions required was detected. I n another series of determinations 1mg. of Orange I was titrated with 0.01 N titanium trichloride, using different quantities of a salt. The results thus obtained for sodium citrate are given in Table 111. One milligram of Orange I theoretically requires for reduction 1.14 cc. of 0.01 N titanium trichloride. When the volume of solution in the flask was 100 cc., however, the quantity used averaged 0.43 cc. higher. This error is attributed to the dilution and would be negligible when 0.1 N reducing solution is used.
Consumption of Amaranth when Different Buffers Are Used BWF- DYE FER
BUFFER
-G.
Rochelle salt 10 -
Tic13 CONSUMED No. 1
G. 0.1 0.3 0.3
5.98 17.00 17.52
cc.
No. 2 cc.
cc.
5.93 1 7 . 0 8 li:Z 17.7 17.62
cc.
5 10
0.3 0.3
16.75 16.95 16.45 16.9 16.4 16.6 16.6 17.1
Sodium tartrate
5 10
0.3 0.3
17.1 17.28 17.0 17.70 17.50 17.6
10
0.1 0.3 0.3
6 . 0 8 6.08 17.8 17.83 17.8 17.8
1
Sodium acetate
1
Sodium bicarbonate
10 5
10
cc.
6.1 5.95 16.85 17.15 17.60 17.65
Sodium bitartrate
Calcium carbonate
KO.5
No. 3 No. 4
5 10
Potassium antimony tartrate
5 10
TiCls (0.01 N )
5.95 6.05 6 . 1 17.8 17.9 17.9 1 7 . 9 5 18.05 1 7 . 9
0.1 0.3 0.3
5.99 6.04 17.80 17.65 17.75 17.7
5.95 17.77
..,
,
. .
0.1 0.3 0.3
5.98 5.92 5.92 5,92 5.98 17.73 1 7 . 7 5 17.78 1 7 . 7 3 17.73 17.75 17.73 17.78 17.73 17.75
0.1 0.3 0.3
5.93 17.73 17.73
5.93 5.88 17.7 17.73 1 7 . 7 3 17,,7
5.93 17.7 17.7
5,88 17.76 17.72
The values obtained for Ponceau 3R (Colour Index 80) when titration was carried out in the presence of sodium tartrate, Rochelle salts, or sodium bitartrate wereveryerratic. When potassium antimony tartrate was used, a sharp end point was not obtained. In the presence of sodium citrate
MG.
ORANGEI
KO.3
No. 2
C.1 100 cc.1 C c . 1.35 1; 1.55 20 1.55
Cc.
Cc.
Cc.
Cc.
1.30 1.95 1.55
1.65 1.50 1.75
1.80 1.35 1.80
1.80 1.40 2.10
..
6.1 6.2 17.95 17.85 17.9 17.9
... ... ..,
1
Xo. 1
...
6.2 6.3 6.2 17.75 17.76 17.76 17.8 17.85 17.8
0.1 0.3 0.3
PER
SODIUX
CITRATE
. ..
~~
Sodium citrate
Table 111-Tests for Blank on Sodium Citrate
16.5 17.0
16.8 17.5
861
I
..
I
..
No. 4
No. 5
..
..
cc.
cc.
10 20 1
20.15 20.12 20.15 20.15
..
..
Conclusion
The color content of Amaranth may be determined by titration with titanium trichloride in the presence of sodium citrate, sodium bicarbonate, or potassium antimony tartrate. That of Ponceau 3R may be determined by titration with titanium trichloride in the presence of sodium citrate or sodium bicarbonate. Orange I may be titrated in the presence of sodium citrate, sodium bicarbonate, or the tartrates, except potassium antimony tartrate. The correct buffer salt must be determined for each dye. The results reported here and those of other investigations (unpublished) warrant the conclusion that, for the correct evaluation of the color content of any dye, the buffer used 4
Kolthoff and Robinson, R e c .
170’Y.
chim., 45, 169 (1926).
COLOR B Y TITRATION IN PRESENCEOF:
DYE
Amaranth Ponceau 3R Orange I
MolsTURE
SODIUM SODIUM WATERETHER CHLORIDE SULFATE INSOLUBLEEXTRACT ~
P e r cent
P e r cent
7.90 9.00 9.55 8.45 5. 72 7.30 3.20
2.40 2.42 3.34 4.14 4.70 3.86 1.74
P e r cent
.. 0.27 ..
0.35 0.31
.. ..
P c r cent 0.08 0.50 0.07 0.25 0.12 0.14 0.16
!
R
Sodium ~ citrate
Sodium ~ ~ bicarbonate
Sodium bitartrate
~
P e r cent
P e r cent
P e r cent
P e r cent
P e r cent
0.05 0.20 0.11 0.12 0.20 0.07 0.07
89.57 87.61 86.93 86.69 88,95 88.63 94.83
89.20 86.60 86.90 85.40 87.87 87.50 93.68
89.30 86.70 86,76 85.50 87.75 87.30 93.47
89.10 86.40
P e r cent
... ...
... ... ... ... ...
*..
87.28 93.68
...
...
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
862
must be tried thoroughly under a great variety of conditions before any reliance can be placed upon them. This may be due to the nature of the dye, but no attempt has been made
Vol. 20, No. 8
by the writers to determine it. However, if the correct salt to use is known, the dye content can be accurately determined.
Coal Conductivity Cell' Eric Sinkinson I,EHIGH UXIVERSITY, BETHLEHEM, PA
The ohmic resistance of powdered coal can be measured with a fair degree of accuracy by using the specially designed cell described herein, in circuit with an ordinary Wheatstone bridge combination. The cell containing the coal is operated simultaneously with a standard cell, into which is placed coal, graphite, or charcoal, according to the type of measurement to be made in the test cell. By this means comparative measurements of resistance can be made with any series of coals properly prepared, provided they are conductors of electricity. A critical examination of the cell and method of using i t has been conducted to determine its usefulness under varying conditions. I t was found that concordant results can be obtained on the same sample, having regard to the
character of the substance and the limits of accuracy of the method. The method may be used in the process of sampling and the comparison of samples, before any other work has been done on them. Measurement of the resistance of a coal before and after boiling with concentrated hydrochloric acid to remove the soluble portion of the ash shows that this treatment lowers the resistance of the coal from 12,730 ohms to 9360 ohms, by the removal of 1.40 per cent of itsash. The resistance of Pennsylvanian and Scotch coals has been compared. Finally, the method has been used to clear up an anomaly, previously found, that the adsorption of carbon dioxide by a bituminous coal is greater than by the fusain taken from it.
HE purpose of this investigation was to devise a method
is from 1 to 600,000 ohms, and settings can be made to 0.1 per cent. OPER.4TIOX-In the lower cell B , place 1 gram of 48-mesh beechwood charcoal, then the central plunger D, the glass sleeve of cell A , into this 1 gram of 48-mesh coal on which the test is to be made. The top plunger closes the test cell. Screw down clamp F until both upper and lower phngers simultaneously compress the charcoal standard and the coal. The pressure is thus evenly distributed through cells A and B. Connect the lower cell to the bridge (not shoKn in figure) by a two-way switch, L. Measure the resistance and in subsequent measurements set the initial resistance at this figure. Turn the two-way switch to connect the upper cell to the bridge and measure the resistance of the coal. To compare coal resistances, change the coal in the upper cell, A , connect the bridge to the lower cell, B , and bring its resistance to the original value. n'ow switch over to the upper cell, A, and measure the resistance of the coal as before. By keeping the resistance of B constant, the coal in A will be subjected to the same conditions and give comparative measurements. The quantities of any size coal used can be determined by weight or specific volume-i. e., the ratio of the weight to the specific gravity.
T
of measuring the electrical conductivity of powdered coal and, by applying it, to study the physical effect of mineral matter and free carbon on coal substance. If a lump of anthracite is ground to a centimeter cube, polished, and the electrical conductivity measured across opposite faces, it will not have the same ohmic resistances along the bedding planes and transverse to them. A test showed an ohmic resistance of 789 across one pair of faces, and 4509 transverse, while in a second sample one pair of faces gave an ohmic resistance of 992 and another 5090. Therefore, before measuring the electrical resistance of coal it must be pulverized to make the mass homogeneous. Even then, the manipulation becomes complicated unless special precautions are observed in packing the coal powder suitably before measuring the resistance. This difficulty is overcome by constructing a resistance or conductivity cell as follows. Description and Use of Cell The conductivity cell consists of two stout glass tubes,
A and B (Figure 1) of uniform bore, 9 cm. long and 1 cm. internal diameter, clamped axially in a vertical position. The units are closed by brass plungers, C, D , E , which also serve as electrodes to make contact with the powdered coal in the cells. The central plunger, D, is common to the cells A and B , and forms an electrical contact between them. The plunger E is fixed to the base frame of a stout metal clamp by an insulator J , through which runs a connecting wire. A similar plunger C held by an insulator, H , is fixed to the top bar, F , of the frame. Plunger C has also a connecting wire fitted through its respective insulator, H . The top bar, F , of the clamp slides on two vertical rods, M A!!, on which are screwed wing nuts, K K . These press down bar F and plunger C and lower it into top cell A . Thus, when coal is placed in cells A and B , the thrust of F is transmitted uniformly through their contents. When in use the' cell is coupled to a Leeds & Korthrup bridge assembly for 60-cycle current. The working range 1
Received March 31, 1926.
Critical Examination of Method One gram of 48-mesh Jeddo coal was placed in cell B and the same quantity in A . The resistance on the dials of the bridge was set at 4000 ohms and cell B connected in circuit. The galvanometer needle was brought to the zero position by regulation of the wing nuts. The upper cell then showed a resistance of 4240 ohms, thereby gi\-ing a relative resistance ratio of 1.06. The process was repeated with a resistance of 3000 ohms in the lower cell, when the upper showed 3090 ohms, giving a relative resistance ratio of 1.03. The contents of the lob-er cell were then replaced by those from the upper, and vice versa. The resistance of the lower cell was set at 3000 ohms, which caused the upper cell to register 2900 ohms, with a relative resistance ratio of 1.03. The relative resistance ratio is therefore constant under the two conditions of operation.
