NOTES ON ANALYTICAL PROCEDURES Simple Automatic Control for Vacuum Systems 1. J. SPADARO, H. L. E. VIX, AND E. A. GASTROCK Southern Regional Research Laboratory, N e w Orleans, La.
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MODIFICATION of a commercial type of Cartesian manostat was so constructed as to bleed air to the system rather than throttle or modulate the vacuum supply. No electrical connections are required and the unit can thus be safely used with systems handling inflammable solvents under conditions where manostats as described by Munch (1) might be undesirable.
OPERATION.This modified manostat is illustrated in Figure 1. The valve unit is adjusted so that the rubber disk, E, rests on the orifice when the lower end of the wire is a proximately 1mm. from the top of the floatin bell. Stopcocks $and H remain open until the vacuum approacfes 10 mm. of the desired reduced pressure. B is then closed, while H remains partially open. The exact reduced pressure desired is obtained by adjusting the rubber disk on the wire. Functioning of the manostat is indicated by the continuous and rapid axial modulation of the valve unit. The operation is produced as follows: Since equal ressures must be maintained in the mercury-sealed chamber, If and in chamber J leading to the system, a change of pressure in J causes an upward or downward displacement of mercury in this chamber, thereby raising or lowering the floating bell, D. This in turn opens or closes orifice G, thus maintaining the equilibrium in the two chambers. A 2-mm. orifice controls reduced pressures down to 200 mm. of mercury (absolute) and a 1-mm. orifice controls pressures between 220 and 30 mm. The reduced pressure in a system can be automatically controlled to within *0.25 mm. of mercu by proper adjustments of the orifice, valve unit, and p e t c o g B. After pro er adjustments are made the pressure can be controlled for &n ingfinite period of time with no drifting of preasure within the system. Two modified manostats as described have been successfully used in the Southern Regional Research Laboratory for several months.
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TO VACUUM PUMP
Figure 1. Modified Manostat A.
Maln body of manostat
B. Uowock
C. Sectlon for m e w r y seal D. Floating bell Valve unit conslats of adlustable rubber disk E attached to e rigld noncorrosive wire, F,kee to move erlelly throuclh'orlkcr G.
LITERATURE CITED
(1) Munoh,
'1
R.H.,J. Chem. Education, 9, 1275 (1932).
Absorption Spectrum of the Antimony TrichloridrErgosterol Reaction Product ALEXANDER MUELLER, Gelatin Products Corporation, Detroit, Mich. of 9122 and an value of 230.0 * 3% (average of 20 trials). Two additional absorption maxima were observed a t 322 mp and 510 mp with E!?m. values of 68.0 and 25.0, respectively. These measurements were performed on a sample of ergosterol which was shown to be 100% pure by a measurement of its ultraviolet absorption spectrum. The absorption maximum a t 393 mp was found to be stable for the period from 2 to 10 minutes following preparation of the antimony trichloride+rgosterol reaction product, making it possible to make very satisfactory quantitative measurements of its intensity. The absorption spectrum of the antimony trichloride-calciferol reaction product shows no absorption bands
D
URING the c o w of investigating the antimony trichloride absorption spectrum of vitamin D a t 500 mp, according to the method described by Nield, Russell, and Zimmerli (S),it was observed that solutions of the antimony trichloride reaction products of irradiated ergosterol exhibit an absorption band a t 393 mp aa well as at 500 mp. Further investigation of the absorption spectra of the antimony trichloride reaction products of pure samples of calciferol (vitamin De) obtained from Winthrop Chemical Co. and of pure ergosterol obtained from Standard Brands, Inc., indicates the absorption maximum a t 393 mp to be due to ergosterol. The absorption maximum at 393 mp is sharp and well defined, having a molecular extinction coefficient 214
