The arc spectrum of selenium, as excited by means of a positive column discharge in helium, has been photographed over the wave-length range 300-11,000A. Four different grating spectrographs were used having dispersions of from 11 to 2.5A per mm. A total of 510 lines has been measured as belonging to the arc spectrum and of these 391 have been classified. Seven series built on the A S state of the ion have been carried to five or more members and the absolute term values are determined to within 0.2 cm" 1 . All the 4£% 4p*(W) 5s, 4£ 3 ( 2 P) 55, and4£ 3 ( 2 £>) 5p terms have been located and also some of the 4=p 3 ( 2 D) Ad terms. Perturbation effects are frequently evident and are illustrated by plots of the various series.
The diagnostic performance of the flat-panel detector is comparable to that of the asymmetric screen-film system for depiction of all simulated patterns of interstitial lung diseases, nodules, and catheters at the same speed and offers the potential of dose reduction to a speed of 800.
The following investigation on the absorption of fluorescein was undertaken in the course of our study of triphenylmethane derivatives.3 The absorption of fluorescein has been studied extensively in the past but the recorded data show wide variations. In the earlier work,4 only solutions of alkali salts of fluorescein were employed. Meyer and Fischer5 prepared a violet solution of fluorescein by boiling it with a concentrated solution of alkali. They called attention to the similarity of its absorption spectrum with that of phenolphthalein in dilute alkaline solution. Medhi and Watson6 and Howe7 compared the absorption of neutral and alkaline solutions of fluorescein in the visible and ultraviolet regions, respectively. Howe also reported on the absorption of fluoran in neutral and alkaline alcoholic solutions. Moir8 studied the visible absorption of fluorescein in coned, sulfuric acid solution. Other reports on the absorption in the visible region were made by Nichols and Merritt,9 Formánek and Knop10 and Holmes.11The lack of concordant results can be ascribed to two causes: (1) using impure materials, such as commercial preparations or extracts made directly from the fusion mixture; (2) neglecting to mention concentrations, both of fluorescein and alkali in the case of alkaline solutions, for 1 The assistance of a grant made to the first two authors from the Heckscher Research Foundation of Cornell University which enabled us to make the measurements described in this report is gratefully acknowledged.
The method employed in the decompositions was a simple one, consisting essentially of a means of dropping the glyceride directly onto the heated catalyst, with suitable provision for condensing and collecting the gaseous and liquid products. The catalyst in all cases was thorium oxide, prepared by ignition of the nitrate, and supported on finely cracked, porous tile. The reaction chamber, containing the catalyst, was a vertical silica tube, 76 by 3.8 cm., electrically heated. Analysis of the liquid products presented considerable difficulty, but the results are believed to be reasonably accurate.The determination of fatty acids was greatly facilitated by the use of their benzyl pseudothio-urea salts, a method suggested by the paper of Johnson and Donleavy.6The results for the four runs thus far completed have been given under the discussion. Summary 1. The catalytic decomposition of triacetin and of tripropionin over thorium oxide has been studied at a maximum temperature of 525°.2. Acrolein, acids, oxides of carbon, hydrocarbons and tarry condensation compounds are uniform products of decomposition. Unexpectedly, hydrogen and the lower homolog of the glyceride acid are also formed.3. The production of the latter substances makes it impossible at present to deduce a reaction mechanism.4. Tripropionin, prepared for this work, is a new representative of the glyceride series.
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