endothermal peaks, one a t approximately 85' C. and the other a t about 175' C. The first corresponds to the melting point of the compound, 87.3' C. The second, although much lower than the reported boiling point of 220.3' C. corresponds to the volatilization of 1,4dibromobenzene from the sample holder. The position of the lamp ensures the existence of a thermal gradient in the system, which provides a driving force for the sublimation of 1,4-dibromobenzene. The aluminum foil inside the cover section was covered with crystals of the compound, confirming the behavior indicated. The thermal gradient will provide a condensing surface for gaseous molecules a t any sample temperature. Thus, nonequilibrium conditions exist providing for continued removal of the gaseous phase and replenishment from the liquid. Because of this, liquid-gas transitions would be expected to give broader peaks, a t temperatures below recorded boiling points. The manually operated system, after application of 6 volts, showed a surge
A Figure 2.
ig
Differential
thermal analysis of 1,4dibromobenzene left. 5 0 % in A1203. M a n u a l control Right. 20% in AI~OI. Programmed voltage
is 1
AT
I 50
I
1
100 I50
I
200 TEMPERATURE, "C.
on thc thermogram, not present when programmed voltage is applied. Thus, a more even application of voltage would reduce the tendency for artifacts in the thermogram. The apparatus is satisfactory for obtaining differential thermal curves
of organic compounds where data belon 240' C. are desired. The equipment is portable. The heating element could be operated on battery-supplied current. The thermocouple voltage could be followed with battery-powered potentiometers.
Simple Apparatus for Microdetermination of Methane Sidney Toby, Chemistry Department, Rutgers University, New Brunswick, N. J.
is often used as a n oxiC dant in the analysis of mixtures of hydrogen, hydrocarbons, and nitrogen UPRIC OXIDE
( 5 ) . Hydrogen burns completely at 250' C. in a few minutes. To burn methane, the temperature of the cupric oxide has to be considerably higher. -4bove 700 ' C., however, decomposition of the cupric oxide interferes with the determination. Catalysts such as cuprous chloride (S), ferric oxide (g), and chromic oxide ( I ) with the cupric oxide have been used in attempts to lower the temperature necessary for combustion. Their efficacy is open to doubt, however, because the temperatures quoted (circa 600' C.) are little lower than are needed with pure cupric oxide. McElcheran, Wijnen, and Steacie (4) found that methane may be completely burned at 570' C. in 12 hours without a catalyst Table 1. Contact Time,
Gas
Sample
0
Found
2.0
CH4 Nz CH, N2
45
CH4 NP CH, ?;2
144 4
The furnace consists of a fused quartz tube containing oxidized copper turnings b e h e e n two plugs of quartz ~ 0 0 1 . The furnace is evacuated before use. Cutoff A is closed and the mercury in the left-hand limb is allowed to reach the calibration line. The gas to be analyzed is pumped through the diffusion pump backed by the Toepler pump, and
Analysis of Mixtures of Methane and Nitrogen
Hr.
3.0
and without repassing the gases through the furnace. By increasing the temperature somewhat the contact time may be reduced to a more convenient value with no sacrifice in accuracy. The limiting factors in accuracy are the errors involved in reading a gas buret. As these errors may be held within =k0,3%, the method is more accurate than mass spectrometric or gas chromatographic analysis.
Gas Quantities, @moles Blank 0 0 0.02
... ...
0 0.17
ANALYTICAL CHEMISTRY
6.72 9.06 6.75 9.01
9.78 4 09 9.84 4.05
16.30 9.55 16.18 9.62
16.50 15.95
23.00 19.39
18:41 16.42 16.23
iO:14 23.24 19.88
measured. The mercury in the Toepler pump is lowerd somewhat to reduce the pressure and cutoff A is opened. The mercury in the Toepler pump is then raised until the float valve in cutoff A is closed. During the combustion Ctube B is kept a t liquid-air temperature. After the combustion a n y nitrogen is pumped off and measured. The Utube is then surrounded,mith a solid methanol slush and the residual carbon dioxide is measured.
Some results are given in Table I. K i t h a furnace temperature of 670” + 2 ” C. and less than 30 pmoles of sample, complete combustion took place n-ithin 2 hours. At this temperature the equilibrium pressure of oxygen over cupric oside is mm. (6); however, equilibrium is reached very slowly, as shown by blank determinations. Samples greater than 30 pmoles needed a longer contact time and the results were
less accurate. Ethane may be determined in the absence of methane at slightly loner furnace temperatures.
ACKNOWLEDGMENT
the cost of apparatus.
LITERATURE CITED
(1) a4raki,s.,J a p a n dnaZyst2,365 (1953). (2) Bruckner, H., Schick, R., Gas u. Wasserfach. 82, 189 (1939). (3) Camubell. J. R.. Grav. T..’ J . SOC. ‘ Chem. lnd. 49,447 (1930): ’ ( 4 ) McElcheran, D. E., Wijnen, M.H. J., Steacie, E. W. R . , Can. J . Chem. 36,
’
C h e k S h . 42, 2603 (1920).
‘
Simple and Inexpensive Polarograph Cell J. L. Monkman, Department of National Health and Welfare, Ottawa, Canada quantitative work of a repetitive F nature, tlie analyst requires a polarograph cell which is rugged, easily OR
cleaned, simple, and inexpensive. With a large number of such cells on hand, the maximum daily output may be obtained from a polarograph. Large numbers of samples can be processed quickly only if a large number of clean cells are available. The cell described has given satisfactory service in every detail for over a year. An earlier design, used for 12 years, was identical, except for a plain end a t A .
as concentrations of 1 y of lead per 1 ml. of cell solution can be determined accurately and consistently. This may be partly due to the fact that a polarogram requires 3 minutes or less. The cells are constructed of borosilicate glass throughout. Only el:mentary glass blon ing experience is necessary to construct conipletrly satisfactory cells. hIercury is added to a level slightly below the connection to the side tube, B. It rises in the capillary arm, C, where the anode connection e mm.
A
Th? total capacity is of the order of 5 nil. The masimum working capacity is about 3 ml. Sample volumes of 1.0 ml. or less are commonly used. The cell cross section was chosen to be 1 sq. em., as recommended b y Majer (1). Because, in routine analysis of known systems, voltage scale calibration is not too necessary, no provision was made for use of the saturated calomel electrode with this cell. Lead, for example, is determined in dilute hydrochloric acid electrolyte; the lead wave occurs entirely reproducibly, and very close to the “normal” voltage position ( 1 , a). The solution is not blanketed with nitrogen during a run in $his cell. There is, however, no apparent interference from dissolved oxygen,
is made by inserting the wire lead into this arm. The 7 j l S/B joint is connected to a fixed nitrogen manifold having matching joints with a spring clamp (available from Arthur H. Thomas Co., Philadelphia, Pa., catalog Xo. 3241). This clamp may, however, be instantly attached or detached. Nitrogen is passed through the side a r m in the direction A to B for the appropriate degassing time. It is convenient to use this cell m-ith a nitrogen manifold having four, five. or six openings, with stopcocks and outer S/B joints. Thus a group of samples may be degassed simultaneously. After the initial sample has been degassed for the necessary time, it is only a question of adding a new cell and sample to the manifold each time a samnle is taken off to be run on the pola&graph. Cells may be cleaned by soaking in chromic acid cleaning solution. The shal-e lends itself readily to cleaning by inversion over a steam jet. Cost of joints for 12 such cells is about $13. Fifteen to 20 analyses of prepared samples may be carried out in 1 hour. LITERATURE CITED
(1) blajrr, I-.> Collection Crechoslov. Chem. Commirns. 7, 146, 215 (1033). ( 2 ) Ibid.,9, 360 (1937.
Modified 4,7-Diphenyl-1 ,lo-phenanthroline Method Sensitive to 1 P.P.B. of Iron in High Purity Water William G. Knapp, Argonne National Laboratory, Lemont, 111.
method of Smith, McCurdy, anti Diehl [Analyst 77, 418-22 (1952)l has been modified t o provide a simple, highly sensitive procedure for the determination of iron in high purity water. The original sensitivity to 10 p.p.b. has been extended t o 1 p.p.b,, and the time per determination has been reduced to less than 5 minutes when sis or more samples are run simultaneously. This modified method has been in routine laboratory use in testing of high purity water from corrosion test loops THE
for several months n-ith completely satisfactory results. Reagents. T h e color-forming complexing reagent, 4,7 - diphenyl - 1 , l O phenanthroline (Bathophenthanthroline), a n d 10% hydroxylamine are retained from t h e original method, though after extensive tests t h e use of sodium acetate as a buffer was discontinued. Of t h e two extraction solvents suggested-isoamyl alcohol and n-hexyl alcohol-only t h e latter is suitable where iron concentrations are less than 10 p.p.b. Technical grade n-
hexyl alcohol contains a trace of iron which interferes with evaluation of samples and standards. Redistillation of the alcohol and elimination of sources of contamination (dust, etc.) are necessary. Standards made with known quantities of ferrous iron stock solution (0.1 y of iron per ml.) are very stable in the absence of impurities or contamination. They gradually darkened where such contamination was encountered. Use of carefully purified reagents made possible the preparation of water-white blanks and progressively VOL. 31, NO. 8, AUGUST 1959
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