This allows easy mounting, simple adjustment, quick removal, and disengagement of any motor while tests are being carried out on the correct positioning of the electrical components of the system. If the gear system is not mounted properly and a n y tightness occurs, difficulty will be experienced in disengaging the clutch; careful alignment is necessary and the clutch teeth should be angled as much as possible. Microswitches A l l and ill2 can be mounted in many ways. One convenient mount is on the side of a rightangled bracket, mounted on the outside of the guide bar support. A slot is cut in the side of the bracket to allow easy positioning of the microswitches. The mechanism of the microswitch is actuated through coming in contact with that part of the guide bar which protrudes through the guide bar support. Each heater unit is constructed from a single loop of No. 26 bare nickelchromium wire attached to copper rods approximately 5 inches long and inch in diameter, and held in place by a Bakelite strip which provides both insulation and a means of adjusting the height of the heater. Each heater is controlled b y a rheostat, wired in the manner of a voltage divider (Figure 4). The type of circuit used gave the best
individual control for each heater. K i t h all the heaters working at maximum temperature the load is about 13 amperes. However, the 6-volt centertapped 10-ampere Hammond transformer worked satisfactorily and there was no indication of heating due to overloading. T o determine the effectiveness of the apparatus a trial run was carried out with mixtures of 1 and 0.1% 2,4-dinitrophenylhydrazine in naphthalene. Approximately 500 mg. of the mixture was heated and drawn into a preheated tube 25 em. long (outside diameter 4 mm., inside diameter 2 mm.), to a height of about 15 cm. Five passes completely removed the 2,4-dinitrophenylhydrazine from approximately 90% of the O.lyOmixture and concentrated it in a 1-em. zone above the point which the heater reached a t the end of each run. Fifteen passes were required to remove the impurity completely from approximately 80% of the 1% mixture, concentration taking place in the bottom 3 cm. of the tube.
development of the equipment, and for assistance in preparing the manuscript, and F. C. Freeman for assistance in solving technical problems and helping to construct the prototype. LITERATURE CITED
( 1 ) Burris, L., Jr., Stockman, C. H., Dillon, I. G., J. Metals 7, Trans. 1017 (, -1-9.5.5 ). - - I .
(2) Goodman, C. H. L., Research (London) 7, 168 (1954). (3) Handley, R., Herington, E. F. G., Chem. & Ind. (London) 1956. 304. (4)zbid., 1957, ii84. ( 5 ) Herington, E. F. G., Handley, R., Cook, A. J., Ibid., 1956,252. (6) Hesse, G., Schildknecht, H., Angew. Chem. 68, 641 (1956). (7) Natl. Bur. Standards (V.S.), Tech. News Bull. 39, 81 (1955). ( 8 ) Pfann. W. G.. Chem. Ena. Y e w s 34. 1440 (1956). (9) Pfann, W. G., J . Metals 4, Trans. 747 (1952). (10) Research Specialties Co., ANAL. CHEX.29, 77A (July 1957). (11) Rock, H., Satu,wzssenschaSten 43, 81 i i a m i ) 112) Schumacher. E. E.. J . Metals 5 . ' 1 2 8 (1953). ' (13) Tanenbaum, lI., GOSS, A. J., Pfann, W. G., Ibid., 6 , Trans. 762 (1954). .
I
\ - /
L
ACKNOWLEDGMENT
The author thanks D . R. Idler for suggesting this project, for advice during
,LYV",'
A Compact Unit for Concentration of Multiple Solutions at Reduced Temperature A. S. Meyer, J. C. Matthews, and P. Samarco, Schering Corp., Bloomfield, N. J. unit described (Figure l), perT mitting concentration of multiple solutions at reduced temperature, has HE
been used in this laboratory for several years. The tubes containing the solutes are
attached to a holder, K , by means of a stainless steel spring which snugly surrounds the slot of the holder (Figure 2). This holder was designed for accommodating 12 tubes with a maximal diameter of 1 inch. (Smaller tubes are retained equally well by the spring, even if they are located adjacent t o tubes of larger diameter.) If Erlenmeyer flasks
A\
are used frequently, it is better to space the openings farther apart; in the construction described, only alternate openings could be utilized w t h these flasks. Air or nitrogen is introduced from the source, G, through a distributing manifold (D,Figure 3), 16 inches of lightweight rubber tubing 1 ; ~inch in internal diameter, B, and an 8-inch long rigid extension tube 7/32 inch in outside diameter, I , joined to a 3 I 2-inch long 18 gage stainless steel needle IT ith a Yale adapter and square-cut needle end, J. The gas flow is directed to the individual needle by a stainless steel stopcock No. MSO 1, C (items I , J , and C are from Becton, Dickinson and Co.). The end of the needle is placed approximately l/? inch above the surface of the liquid t o p e evaporated. The extension. I , held in
I 7 !I
,D.HoleThru
YD Hole(Threod1for
C H o l e Thru Both Pcs. Fasten Holderto Hub with 3-+"D Screws 120°Aport
Figure 1.
Solvent evaporation unit
Side view drawn to scale 966
ANALYTICAL CHEMISTRY
Figure 2. Test tube holder Cross sections top and side, drawn to scale
4-;"Holes (Thrlad)
Air Chamber
to Secure Manifold to Lucite Disc
Figure 3. Manifold Cross section, d r a w to scale
place by a clip, E , passcs through a perpendicularly adjusted stainless steel sleeve inch in internal diameter, F , which is push fitted intci a Lucite disk of inch thickness, H . The latter serves a t the same time as a cover. Lucite cover (fastened to the manifold, D)and tube holder K are, a t a working distancc of approximately 51/2 inches, both attached by a iTing screw, L, to a X 22 inch rod, A . This shaft rests in a 2-inch high c0ppf.r block, S,n ith a cylindrical
hole I / S ~ inch larger than the rod dianieter and freely rotating. The shaft seat. -i',is silver soldered onto thc pan, -11, in which the water is heated by a circular immersion heater and thermostatted at the desired temperature. If Erlenmeyer flasks are used, a wider pan is required or alternatively a bulge has to be nelded to the front of the pan. The advantages of this unit are obvious. For speedy operation a simple
attachment of the tubes is reqLiired, here brought about by the use of a spring. A facile n a y of adjusting the erld above the solvent surface has been achieved' rotary arrangement is convenient and 'pace saving* The general Principles of this construction can easily be adapted for similar purposes. (A similar unit is now available from Organomation Associates, Turnpike Sta., Shrewbury, Mass.).
Continuous-Feed Rotating Evaporator Gunter Zweig, Pesticide Residue Research laboratory, University of California, Davis, Calif. N
AN
a11-glass, continuous-feed ro-
ISAL. tating evaporator described b y Kohn CHEM. 28, 1061 (1956)] the evaporating flask was driven by a belt, made from a rubber band, connected to a pulley on a laboratory stirring motor. Because of difficulty due to slippage of the belt, another evaporator was assembled, which utilizes c.ommonly available equipment. This evaporator has been in use in this laboratory for sevwal months, concentrating large amounts of acetone and alcohol solutions of plant extracts.
The continuous-feed, rotating evaporator consists of a Rinco evaporator, 1; Rinco special condenser flask with $24'40 neck, 2; adapter with $24 '40 inner joint and SB28/15 outer joint, 3; adapter n i t h SB28/15 inner joint and $24140 outer joint, 4 ; condenser with $24140 joints, 5 ; vacuum adapter with $24,'40 joints, 6; round-bottomed flask with 24/40 joint (500-ml. size), 7 ; T12/30 inner joints, 8; and 3-liter separatory funnel, 9. Adapter 4 is clamped tightly to a ring stand, so that condenser flask 2 and adapter 3 are turning while the evaporator is in operation. The solution is fed
sa,paratol)l tunnel
n
to vacuum
1
from the sepamtory funnel a t a constant rate, which is regulated so that the level of the liquid is constant in the condenser flask, which is actually serving as the evaporating flask. The level of liquid is kept 2 inches be1oIv the opening, 10, to prevent splashing. The receiving flask, i , is kept a t room temperature, so that vapors do not collect and operation may be continuous. All glass connections are well greased with silicone stopcock grease. By using a u-ater aspirator a t about 25 to 30 mni. of mercury pressure, 2 liters of a n acetone eytract from potatoes or green leaves may be concentrated to dryness in less than 1 hour. The concentrate is then transferred from the condenser flask with several washings of acetone. Solutions containing mineral acids should not be concentrated, because the metal shaft of the Rinco evaporator nil1 corrode slightly. Substitution of a stainless steel shaft overconies this disadvantage, as the solution that passes through the metal shaft is a t ambient temperature. The relatively high cost (about $100) may discourage routine use of this evaporator in some laboratories.
Base-Line and Maximum Value Methods in Infrared Quantitative Analysis
H. L.
Cupples, Entomology Research Division, Agricultural Research Service, U. S. Department of Agriculture, Beltsville, Md.
-4 STUDY of the susceptibility of infrared base-line methods to errors caused b y overlapping bands of unknown constituents not present in the calibrating solutions, base-line determinations were made of y-benzene hexachloride (BHC) in admixture with its isomers, which were considered for this purpose to be unknown impurities.
IN
Spectra were taken in carbon disulfide solution on a single-beam recording spectrophotometer, and the relevant points converted to per cent transmittance. All base lines were drawn from the curve intersection with the ordinate a t the selected wave length, parallel to
the zero energy line. A t 15 selected wave lengths in the 7.5- to 15.0-micron range, 27 base lines I\ ere established (tm-o each a t 12 of the wave lengths), and, using purified y-BHC, graphical calibrations were determined for each base line. All these calibrations, therefore, were valid for a y-BHC-carbon disulfide system; the base lines were drawn in a uniform manner, none being specially chosen for use in the presence of the isomers or a n y other specific impurities. Then y-BHC was determined in a carbon disulfide solution containing 15.0 grams per liter of 7-BHC in admixture with 15.0 grams per liter of its isomers, the isomers being present in
proportions approximately that of technical BHC. Figure 1 sho\vs determined amounts as percentages of the true amount. Of the 27 determinations only nine are within + l o % of the true amount, and many are seriously in error. It is evident that a n indiscriminate application of baseline methods to mixtures of unknown qualitative composition may result in large errors. If, however, the spectra of the sample and known components are compared, and the analytical wave lengths and base lines chosen with reference to them, better results will be obVOL. 3 1, NO. 5 , M A Y 1959
e
967
