ANALYTICAL CHEMISTRY
428 In Table I values for gel and cure t!me and peak exotherm temperature are given for t v o commercial polyester resins, each catalyzed, respectively, x i t h 0.5, 1.0, and 2.0% by weight of benzoyl peroxide. The catalyst was added as a 50% paste of benzoyl perovide in tricresyl phosphate, Luperco ATC. Five samples of each resin at all three catalyst concentrations were tested with both the miniature hypodermic needle thermocouple and a ‘/s-inch commercial iron-constantan thermocouple. The thermocouples xere alternated on each successive individual test t o minimize any possible development of a pattern. The t n o thermocouples were compared at various temperatures and were found to agree exactlj- when measuring the temperature of a large mass.
Table I. Catalyst Concn.. Added Benzoyl Peroxide,
%
Resin A 0 5
Time, N i n . Gel Cure 3 8 3 8 3 8 3 7 3 8 3.8
6 6 6 6 6
2.oa
Resin B 0.5Q 1.0“
AV.
1. 0 a
2 a
Comparative Exotherm Data Hypodermic Needle Thermocouple Peak
oa
ti::I;,, F.
5 5
419 419
5
421
3 5 6.5
2.7 1.8
Commercial Thermocouple Peak Time, l f i n . Gel Cure
F.
419 419 419
4 2 4 3 4 2 4 2 4 2 4.2
7 7 7 6 6 6
0 0 0 8 8 9
37R 379 3761 381 383 379
4.3 3.1
439 453
2.7 1.6
4.3 2.8
so1
8 3 4.9
11.2 7.0
408 421
10.1
5.5
12.3 7.0
378 394
3.0
4.6
435
2.7
4.0
401
414
Aerosol Chromatographic Spray Gunter Zweig, Charles
F.
Kettering Foundation, Yellow Springs, Ohio
the visualization of amino acid chromatograms a ninhydrin Fspraying . or dipping solution has been commonly employed OR
(Block, R. J., Durrum, E. L., and Zweig, G., “Paper Chromatography and Paper Electrophoresis,” Academic Press, Yew Tork, 1955). For small sheets (8 square inches) the dipping technique has been found satisfactory. Large sheets (18’/4 X 22l/2 inches), however, can be sprayed more easily. Several models of sprayers for chromatography are commercially available or can be made a t home (Block, R. J., Durrum, E. L., and Zweig, G., “Paper Chromatography and Paper Electrophoresis,” Academic Press, S e w I-ork, 1955). In order t o obtain a uniform spray, a source of compressed air should be available. Furthermore, if norking with a number of different spraying reagents simultaneously, it would be cumbersome to emptr, clean, and refill the sprayer each time when changing solutions. Therefore, a cheap, disposable and portable spray gun is t o be desirable. .4n aerosol bomb seemed to satisfy these conditions. Aerosol-ninhl-drin bombs for spraying large amino acid chromatograms have been used by this foundation. Excellent results n ere obtained M ith ninhydrin dissolved in acetone or n-butyl alcohol. The bombs were prepared by Xeropak, Inc., Chicago 37, Ill., and may be obtained from Scharr & Co., Chicago, 111. The foundation is planning to design other aerosol chromatographic sprays to be used for chromatograms of sugars, organic acids, keto acids, steroids, and other compounds.
Arithmetic average of 5 consecutive tests.
Simplifled lsoteniscope S. A. I n Table I, the data show that the hypodermic needle thermocouple consistently gave peak evotherm temperatures 30” to 40” F. higher than a commercial ‘/*-inch couple. Individuals having occasion t o use any system employing fairly large masses of polyesters, and desiring more accurate measurement of the peak exotherm temperature and resin characteristics, may find good use for this thermocouple of improved design, reproducibility, and accuracy.
Preservation of Ninhydrin-Amino Acid Chromatograms Gunter Zweig, Charles
F. Kettering
Foundation, Yellow Springs, Ohio
order to preserve ninhydrin-treated paper chromatograms, I-uKawerau [Kavierau, E., and X e l a n d , T . , Suture 168, 7i-78
(1951)] recommended dipping the papers first into a copper nitrate solution and then into a chloroform solution of methyl methacrylate. The following modification of this technique was found t o be successful. The ninhydrin-treated chromatogram is dipped into dilute copper nitrate ( I ml. of saturated aqueous copper nitrate and 0.2 ml. of 10% volume by volume nitric acid, diluted to 100 ml. with ethyl alcohol). The papers are then quickly neutralized in vapors of ammonia and are air dried. The papers are then sprayed with Krylon permanent crystal clear acrylic spray, available as an aerosol bomb (Krylon, Inc., Philadelphia 46, Pa.). The chromatograms, thus treated, are stable without any further precautions for months.
Greene’, Air Reduction Co., Inc., Research laborotories, Murray Hill, N. J.
SIMPLIFIED apparatus equivalent
to the Smith-Nenzies isoteni-
A scope [Smith, A., and Nenzies, A. IT. C., J . Am. Chem. SOC.
32, 1412 (19lO)l was developed to obviate the difficulty of filling the classical isoteniscope with viscous organic liquids. It can also be used satisfactorily for any system in which the substance under investigation is the confining liquid,
t
The liquid is pipetted into the lower reservoir (open leg), then the sealed leg ( a piece of glass tubing 7 mm. in diameter and 50 mm. long) is dropped in. The apparatus is connected to a standard manometric system and thermostated. Air, trapped in the sealed leg arhich rests against the bottom of the reservoir, forces the liquid level in the sealed leg below that in the larger open leg. As the apparatus is brought to temperature and moderately evacuated, the level in the sealed leg will fall; a stream of bubbles will rise from the open end of the sealed leg and pass through the open leg. Trapped air is thus removed and the liquid boiled out. Liquid levels in both legs are brought to the same height and the pressure noted. The boiling out procedure is repeated until agreement between readings is obtained.
Values of vapor pressures obtained with the modified and classical isoteniscope agree within experimental error. A further advantage of the modification is that gentle boiling stirs the liquid and ensures rapid temperature equilibration between bath and liquid. 1
Present address, Aerojet-General Corp., -4ZUSS, Calif.
