V O L U M E 24, NO. 7, J U L Y 1 9 5 2
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manometer. The right arm of the U-tube was provided with a stopcock leadinx to the manometer and to the vacuum system
contact in the minostat, actuating an electronic relay which in turn controlled two double-pole douhle-throw power relays, rrhich in turn alternated the current supplied to Glas-col heaters on the still pat between two variable transformers set t o e.m.f. output differentials of 5 to 7 volts. The variable transformers aere manually adjusted during distillation, so that the e.m.f.
.
tions were restricted to pressures above 30 mm. of mercury in the fractionation of decanes and undeennes, so that no data are available on really high-vacuum operation. In general, the operation of the electronic manostats was affected by the constancy of pressure of the vacuum system. For the authors' purposes, the Cartesian manostats of t.he Emil Greiner Co. were used, suitably hdlasted to obtain constant operating pressures (to smooth out transitory pressure variations). Pressure drifts over a period of time had little effect on operation of the electronic manostat, as they affected both sidcs equally.
.
LITERATURE CITED
RUE.
The use of a nitrogen bleeder to keep vapors from the still pot out of the manostat w m found to be optional. By using a coiled length of a/,,inch copper tubing to connect the still pot and manmtat ( 5 ) vapor oontamination in the manostat WBS Rubstantially avdided. With this m n o s t a t , the operating pressure variation was found to be less than *0.035 mm. of mercury or approximately 1% of the hack pressure. Vihrations in the laboratory building appear to induce minute oscillations in the suspended brass chain electrode, causing quicker meniscus breaks than might have been rxpected. The large volume capacity of the U-tube acts as a mechanical analog of an electrical condenser and makes the manmtat insensitive t o transitory vapor pressure variations caused hy uneven boiling in the still pot. Because of its rugged construction, the manastat can withstand moderate mechanical shocks and needs no hacking hoard or special mouths; it can he secured in the desired position with ordinary laboratory damps. \\hen R viscose lubricant is used on the aindlass joint, the high mechanical advantage prevent8 the weight of the brass chain from decreasing the contact distance, but if desired, the joint may be clamped. A manostat of this type was used for more than 2500 hours of dist,iIlation time without any attention other than manual manipulation of tho stopcocks and the windlass. This work was chiefly concerned with the fractionation of thermally stable paraffin mixtures, so that most of the work was carried out a t atmospheric pressures. Reduced pressure opere,
(1) Hall and Palkin. IND. END.CHEM..ANAL.ED., 14, 807 (1942). (2)Hershberg and Huntress, Ibid., 5 , 344 (1933). (3) Podbielniak. Inc., private communication. (4) Runckel and Oldroyd, IND. END.CHEM.,. ~ N A L ED.. . 18, SO (1946). (5) Serfass. Ibid., 13, 263 (1941).
Improved Drilling Jig for Preparation of Porous Cup Electrodes. S. H. Simonsen, Universitv of Teras, Austin, Tex. of porous cup electrodes using a jig of the I designpreparation proposed by Feldman [ANAL.CHEM., 21, 1041 N TBE
(1949):
U. S. Atomic Energy Commission, AECD 23921, if sufficient, pressure was applied t o the jamming cylinder to prevent turning of the electrode during drilling, many of the electrodes were mushed. On the other hand, if less pressure wan applied, the electrode turned in the jig, and the tooth on the jamming cylinder scored a deep groove around thc eireumfc~enc~ of the electrodr, a h resulting in breakage.
Figure 1. Drilling Jig
To eliminate this breakago, a Yimple jig (Figure 1 ) was designed in which the electrode is held firmly, without teeth or vertical line constraints [Owen, L. E., ANAL. CHEM.,22, 1581 (1950)],in a slotted brass chuck brmed to a steel base plate. Figure 2 shows the essentials of construction, The only critical dimensions me: the height of th8 top of the chuck above the base plate, determined by the length of electrodes used; and the diameter of the chuck, which should be only slightly larger than the diameter of the electrode. The base plate is made of 0.5-inch oold rolled steel and iS 4 inches square to provide ample space for clamping t o the bed of the drill press. For removal of tho graphite dust produced during the drilling operation, a slot 0.5 inch wide by 0.125 inch deep is milled in the base of the chuck before brazing it to the base plate. The dust is then readily blown out with a jet of compressed air. An adiustahle depth gage, made by turning a brass screw with a Figure 1. Electronic Manostat A.
Vacuum or atrnosDhero
C.
Brass chain
D. E.
M. P.
R. S. T.
Stillpot Plstinum electrodes Msnometer Sealing wax plug C o ~ p e rwire Standard-taper j o i n t windlass Triethylene dyool
scribed on toD of the collar and base late when both surfaces were flush. Far use, the drill tip is touched lightly to the collar of the depth gage, which is raised to a height corresponding to the desired floor thickness, and the vertical stop of the drill press is adjusted so t.hat at maximum travel the drill will give the correct depth of cut. The jig is aligned with the aid of a bmss rod of the same dlWBS
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ANALYTICAL CHEMISTRY
mensions as the electrode to be Dreuared. The rod. with a center
the jig;th, chuektightened, and the hole drilled:
c I Inch
Figure 2.
3
Drilling Jig
ed by the preparation of 108 electrodes. Of mese, only one was broken and this one was suspected to have been cracked during the cutting t o length. There n.as no tristing of the electrode during drilling and no marlis were produced on the outer surface. The time required far processing one electrode, including cutting t o length, facing the end, and drilling, mas 2 minutes.
shelim&mial is Lucite. Thearmsof the shell aremachined normal to their bores and are sealed by Teflon disks retained by screwed caps of Lucite. In operation, materials of differentcolors are blended, as judgcd by the eye, in a very few minutes. No separation of the mat,erial mass is noted except for the planned division per revolution. Blending times for specific applications must be determined, but usually overnight run8 are sufficient. The unit operates without attention, and blends with infinite patience. It has proved to be a useful laboratory tool, superior to rolling tumbling counterparts.
ACKNOWLEDGMENT
Magnetic Stirrer for Cryoscopic Determinations. Joseph L. Rabinowita, Department of Physiological Chemistry, University of Pennsylvania, Philadelphia, Pa.
The author n-isbes to express his appreciation t o Eugene Berg and A. E. Rymer for their assistance in testing aud fabricating the jig, and to The University of Texas Research Institute for a grant which made this work possible.
HE diagram represents an all-glass magnetic stirrer that has Theen successfully used in this laboratory. Constructed by James Graham, it proved satisfactory in the cryoscopic determination of molecular weights a t higher temperatures.
Twin-Shell Micrablender for Powders. Louis E. Owen, 117 Gorgas Lane, Oak Ridge, Tenn. T IS
often desirable in a spectrochemical laboratory to be able
I to mix powders very thoroughly for the preparation of stand-
ards or analysis matrices. The standard technique far this aperrttion is grinding in a mortar. Such grinding is s laborious process, requiring attention even when power-driven mortar and pestles are used. A concomitant problem is the contamination of a sample with the elements of the mortar material. This is serious in the case of extremely hard materials such as beryllium carbide. Suoh materials, however, may often be powdered in Plitttnertype mortars without marked introduction of foreign elements. Crushed samples of this genre usually can be screened through 8. silk sieve and the dusts (
