of this material in attempting to charge it as a melt or in various solvents. Our spectrum differs considerably from that of McLafferty and Gohlke ( 2 ) . Whereas they obtained a sensitivity for the base peak, m/e 149, of only 3% of that of the m/e 92 from toluene, our value is 38%. The sensitivity of the parent in our spectrum is 86% of that of the base, while McLafferty obtained 18%. McLafferty employed the glass, Teflon, and stainless steel inlet system described by Caldecourt (1) which operates a t about 1-mm. pressure. It appears probable that the low sensitivity values they obtain for iso-
and terephthalic acids result from thermal decomposition and/or incomplete sample vaporization. As they indicated (Z), terephthalic acid does decompose a t 2.50’ C. R e find the products of decomposition to be benzoic acid and COe, proceeding a t a rate of about 1% per minute.
We thank J. L. Taylor and Louis LeBlanc for their general assistance, suggestions, and testing work during the design and fabrication of the glass equipment.
Additional applications of the use of the solids inlet system include direct pyrolysis studies and the determination of more volatile components deposited on or in admixture with more refractory materials.
(1) Caldecourt, V. J., ANAL. CHEM. 27,1670 (1955). ( 2 ) McLafferty, F. W., Gohlke, R. S., Ibid., 31,2076 (1959). (3) O’hseal, M. J., Jr., Wier, T. P., Jr., Ibid., 23,830 (1951). (4) Purdy, K. M., Harris, R. J., /bid., 22, 1337 (1950).
ACKNOWLEDGMENT
LITERATURE CITED
Construction of Thermopiles from Fine Wire Clyde A. Glover and Ruth R. Stanley, Research Laboratories, Tennessee Eastman Co., Division of Eastman Kodak Co., Kingsport, Tenn.
A
paper on an apparatus for the ebulliometric determination of the number-average molecular weights of polymers (3) described the use of an 80-junction thermopile as a temperature-sensing device. The development of the apparatus required construction of a suitable thermopile which could be installed in the ebulliometer. Although several methods have been described for construction of thermocouples (1, 2, 4, 8) and of thermopiles for special purposes (5-7), none were applicable t o this problem. The method described here not only met the requirements of the immediate problem but has been used to make thermopiles containing more than 80 junctions, and is applicable in general to the construction of thermopiles from fine wire. RECEKT
APPARATUS
Only tivo devices which might be considered special w r e used in the construction of the thermopile. The first consisted of a small screw driver, mounted horizontally in a short section of glass tubing, and a small magnet.
A Guide
B
Figure 1. struction
‘copper
Form for thermopile con-
This device was used to twist the pairs of wires prior to welding them. The second device, used for welding the twisted wires, consisted of two sharpened carbon electrodes (ordinary lead pencils) mounted vertically so as to give a spark gap of approximately ‘/8 inch. A current of 7600 volts a.c. a t 18 ma. was supplied to the electrodes and controlled by means of a tap key in the primary circuit. It was convenient in practice to mount the electrodes, along with a 20-power magnifier, on a micromanipulator. PROCEDURE
In the diagrams pertaining to construction of the thermopile, the scale is distorted to show detail better. First, a form was made from three pieces of thin cardboard, cut as shown in Figure 1,A. The width of the outer pieces was about 1 em. less than the desired length of the thermopile. The inner piece was about 2 em. wider than the outer pieces. All pieces were the same length. The length can be varied according to the number of junctions desired. The three pieces were placed together and taped, with ordinarj- cellophane tape, as shonn in Figure 1,B. Copper wire (0.0015 inch in diameter) was wound in a continuous helix around the form, with sufficient escess nire a t the ends to serve as lead wires. Kext, guides of some suitable material, usually a fine wire, were placed over the copper wire on both sides of the form and taped as shown in Figure 1,B. Constantan wire (0.0015 inch in diameter) was then wound in a continuous helix on the form over the guides, crossing the copper 11-ire in all cases a t the edge of the outer boards of the form (Figure 2,:4). Each crossover point of the wire was taped securely to the board on both sides of the form. All wires, except the leads, were clipped at the outer edge of the form. The pieces of the form were then separated and the inner piece was discarded. This left essentially two thermopiles in the stage shown in Figure 2,B.
The form was then mounted on a rigid support, and each pair of vires was twisted by placing the screw driver blade below the wires, which were then clamped mechanically to its surface by the small magnet. Actual twisting was accomplished by rotating the screw driver. Each twisted pair of wires was welded autogeneously; thus, simultaneously, the insulation was removed and a junction was formed. Welding could be done with a micro gas flame, but it was preferable to weld with a highvoltage electric spark of very short duration by using the device previously described. Two precautions ivere necessary in welding: Good contact had to be made between the metals; and the heating had to be sufficiently rapid to minimize oxidation of the !vires adjacent to the weld. Use of nitrogen, which was allowed to flow from a tube near the electrodes and surround the junction during welding, was helpful for this purpose. Continuity and resistance could be checked from either lead to any junction by making contact a t the junction through platinum-tipped forceps used to grasp the weld just tightly enough to establish electrical contact. All junctions were insulated with a Glyptal resin and either baked or air-dried until the resin became hard, The thermopile was then freed from
-\
-..-Copper
L’Conrtonton
A
B
Figure 2. Wire layout for thermopile construction VOL. 33, NO. 3, MARCH 1961
477
the board by carefully removing the tape. The junctions were collected a t the center of the board by sliding them along the guides, and the thermopile was tied a t several places with fine cotton thread. The guides were then clipped near the thermopile and carefully removed. The therniopile was thus left free and ready for installation. ACKNOWLEDGMENT
The authors thank D. C. Sievers
13) Glover. C. A. Stanlev. R. R..AXAL. CHEW33, 447 (1961). (4) . . Haaer. K. F., Rosenthall, M., Ross, W.j Gas J . 49 ( S o . l o ) , 87 (1950). ‘ ( 5 ) Harris, L., J . O p t . SOC.d m . 36, 597
for his interest and suggestions and J. B. Engleman for assistance in the electrical aspects of the problem.
~I
oil
LITERATURE CITED
(1946).
( 6 ) Mason, L. S., Rec. Sei. Instr. 15, 205
(1) Am. Inst. Physics,
“Temperature. Its Measurement and Control in Science and Industry,” T-01. 1, Reinhold, SeJT Tork, 1941; T’01.(2,1955. ( 2 ) Dykp, P. H., ‘Thermoelectric Thermometry,” Leeds 8: Sorthrup Co., Philadelphia, Pa., 1954.
(1944). ( 7 ) Strong, J., ‘.Procedures in Esperi-
mental Physics)” p. 305, Prentice-Hall, Xew Tork, 1943. (8) Sntter, D. RI., Brock, J. E., Proc. Indiana d e a d . Sci. 6 3 , 266 (1953).
A Method for Determining Barium-140 and lanthanum-140 in a Mixture of the Two Radioisotopes William B. Lane, U. S. Naval Radiological Defense Laboratory, San Francisco 24, Calif.
of barium and lanR thanum iTere used to prepare synthetic fallout for studies of conADIOISOTOPES
taminating events arising from nuclear detonations. Dissolution of the kilocurie supply frequently gave a solution enriched in LaI4o, and it was necessary to know the amounts of the components so that aliquots of the solution could be adjusted to ensure a preselected activity (disintegrations per second) when equilibrium was re-established some six days later. A large number of leaching tests n ere conducted on the synthetic fallout to determine the solubility of the radiotracer and this also involved measuring samples which were enriched in one or the other component. The relative amounts of Ba140 and La140 and the total disintegrations per second \\ere determined with a scintillation counter, using a NaI crystal, and a 4-pi ionization chamber, since these instruments were available at the field test site. Both detecting systems are energy-dependent, as shown in Figure 1 ( I , 2), and nhile scintilla-
desired. When the relative amounts of the two components \\-ere established, total disintegrations per second 17-ere found by referring to the second curve s h o m in Figure 2 . This curve gives 4-pi ionization chamber response as function of composition. Thus if a sample were found to be composed of 20% La140 and 80% Bala the average disintegration per second would produce a n ionization current of 5 x 10-14 ma.
tion crystal response decreases n ith increasing gamma energy, the 4-pi ionization chamber response increaqes. The average energy for the two radionuclides is ( 3 ): E La-r40 E
Ba-140
=
=
0.130 m.e.v. per photon 0.910 m.e.v. per photon
and this difference is large enough to permit semiquantitative assay of a mixture of the two isotopes. The gamma radiation from a n aliquot of solution was measured in both instruments in a fixed geometry, and a ratio, r , of the two values taken. r =
LITERATURE CITED
(1) LaRiviere, P. D., “Response of a Low-
Geometry Scintillation Counter to Fission and Other Products,” U. S. Saval Radiological Defense Laboratory TR303 (Feb. 4, 1959, unclassified). (2) Miller, C. F., “Proposed Decay Schemes for Some Fission-Product and Other Radionuclides.” E. S. Kava1 Radiological Defense ’ Laboratory TR160 ( M a y 27, 1957, unclassified). (3) Lliller, C. F., “Response Curve8 for USSRDL 4-Pi Ionization Chamber,” U. S. Saval Radiological Defense Laboratory TR-155 (May 17, 1957, unclassified).
ma. (4-pi ionization chamber) counts/second (scintillation counter)
This ratio depends on the composition, and a calibration curve, shorn in Figure 2, was prepared from known mixtures. The slope of the curve shows greater sensitivity for barium-rich mixtures; however, the over-all accuracy of the method was better than lo%, which was adequate for the information
I
I
I 90
01
70
ENERGY IMEVl
Figure 1. Photon response curves for USNRDL 4-pi ionization chamber and scintillation counter ANALYTICAL CHEMISTRY
60
Lo
10
PHOTON
478
80
0
-0
20
30
4o
50
40
50 60 80’~’I P E R CENT1
40
:5
30
20
10
0
70
80
90
100
( P E R CENT1
Figure 2. Ratio curve for determining composition and response curve for determining activity
