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(7) Clifford, P. A , , and TTichmann, H. J., Ibid., 19, 130 (1936). (8) Corning Glass Works Catalog, “Glass Color Filters”. (9) Dahle, D., J . Assoc. Oficial Agr. Chem., 20, 505 (1937). (10) Evelyn, K. A., J . Biol. Chem., 115, 63 (1936); 117, 365 (1937). (11) Exton, IT. G., Proc. SOC.Ezptl. B i d . X e d . , 21, 181 (1924). (12) Gerrite, H. W., J . Assoc. Oficial A g r . Chem., 22, 131 (1939). (13) Gibson, K. S., J . Optical SOC.Bm.. 25, 131 (1935). (14) Gibson, K. S., and Tyndall, E . P. T . , Bur. Standards, Sci. Paper 5475, 1923. (15) Hardy, J. D., and Pfund, A. H., unpublished xork, 1930. (16) Hillig, F., J . Assoc. Oficial AQT.Chem., 20, 130 (1937). (17) Hubhard, D. M., ISD.E N G .CHEJI.,Anal. Ed., 9, 493 (1937). (18) Ives Tint Photometer, Palo Co., Xew York, N. Y. (19) Jones, L. A , J . Optical SOC.Am., 4, 420 (1920). (20) Judd, D. B., Ibid., 23, 359 (1933). (21) Klein, A. K., and Vorhes, F. A., Jr.. J . Assoc. Oficial Agr. Chem , 22, 121 (1939). (22) Markwood, L. K.,Ibid., 22, 427 (1939).
VOL. 12, NO. 4
(23) Mellon, M. G., “Role of Spectrophotometry in Colorimetry” and cited references, IND.EXG.CHEW,Anal. Ed., 9, 51 (1937). (24) Miiller, R . H., Ibid., 7, 223 (1935). (25) Munsey, 1’.E., J . Assoc. OficWl Agr. Chem., 21, 331 (1938). (26) Murray, C. IT., and Ryall, A. L., ISD.EBG. CHEM.,Kews Ed.. 17, 407 (1939). (27) Pfund, A. H . , J . Optical SOC..4m., 18, 167 (1928) : 19,387 (1929). (28) Priest, I. G., J . Research h’atl. Bur. StandaTds, 15, 529 (1935). (29) Shook, G. A , and Scrivener, B. J., Rev. Sci. Instruments, 3, 553 (1932). (30) Singh, B. K.,and Rao, N. K. A., Plant Physiol., 13,419 (1938). (31) Staats, E . M., J . Optical SOC.Am., 28, 112 (1938). (32) Thiel, A., and Thiel. W., Chem. Fabriic, 5, 44 (1932). (33) TYilson, J . B., J . Assoc. Oficial Agr. Chem., 22, 393 (1939). (34) F i n k l e r , W.O., Ibid., 21, 220 (1938). (35) Ibid., 22, 349 (1939). (36) Zeiss Pulfrich Photometer, Mess 431, Carl Zeiss, Inc., New Tork,
s.Y .
Heat Control Units JOHN A. RIDDICIC Research Department, Commercial Solvents Corporation, Terre Haute, Ind.
T
HE most common laboratory methods for controlling
the temperature of heating elements involve the use of polarized rheostats and lamp banks. The field, or point contact, rheostat gives a stepwise change in temperature. The Forsythe, or sliding contact tube, type gives a more uniform temperature change but has the disadvantages of being a hazard when used on 110- or 220-volt circuits, because of exposed live metal parts, and of “sweating” when watercooled. The lamp bank is usually constructed of porcelain receptacles with exposed terminals, and a close control of the heating element is impossible. All three control units generate heat and the lamp bank emits light that is usually unwanted and badly placed. Of the three methods mentioned, the Forsythe rheostat is the most satisfactory, as it occupies a relatively small space and polarized hookups are easier to make.
I
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T h r e e - P o l e Conveniance Receptacle
FIGURE1. SCHEMATIC WIRINGDIAGRAJI G . Identified or ground nire L. Xeon glow lamp, 1 watt S. Snitch, P & S, Despard V . Variac, Type 200-C
The introduction of the non-vacuum-jacketed fractionating column, such as the Penn State type, into the analytical laboratory necessitated a closer control of heat than was possible with the field rheostat and a safer control than was possible Ivith the Forsythe instrument. The number of heating ele-
ments in the jacket of a fractionating column depends on its length and the use for which it is designed. Since laboratory fractionating units are made of glass, the number of wires in the heated jacket type should be a t a minimum to allow unobstructed vision and placement of thermocouple leads. The minimum number of leads to the heating elements is one more than the number of elements, An ideal heat control would allow its use with any column on the rack. This necessitates a certain amount of standardization in attachment plugs and the control unit. The variable autotransformer has been found to overcome the disadvantages mentioned, and the panel type is suited for incorporation in a control panel of maximum adaptability. There are several such instruments on the market. The T’ariac, Type 2O0-CUJ manufactured by the General Radio Company, Cambridge, Mass., has been used in these laboratories and has given excellent service. For general laboratory work the 860 volt-ampere instrument has proved satisfactory. The three panels described below have been found to meet any need that has arisen in these laboratories since the control panel was developed two years ago. They are constructed to give maximum safety with judicial use, and mag be used as wall panels or set on the laboratory desk top. The first panel developed mas a two-autotransformer unit, the schematic miring diagram of which (front view) is shown in Figure 1. The symbols used are the common conventions except those 8 for the convenience receptacles. The connections to the three-pole convenience outlets in all diagrams are numbered to call attention to the uniform connection of poles with the controls. These positions are determined from the connections of the A center, or common, B three-pole c o n v e n i e n c e FIGURE2. ALTERNATELOAD The left autoPOSITIOSS transformer connects to
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‘P’ T
*
ANA1,YTICAL EDITION
APRIL 15, 1940
the upper receptacle terminal, the right one to the lower receptacle terminal. The identified wire is connected according to the receptacle. The maximum number of heating units that may be used with this panel is two. For individual control of two heating units in parallel with a common lead, the attachment plug is plugged in the common, or center, three-pole convenience receptacle. This circuit is shown in Figure 2, B. The left autotransformer controls the lower heating unit and the right autotransformer controls the upper unit. The identified wire is connected to the right terminal of the receptacle. If the attachment plug is plugged in the left-hand three-pole convenience receptacle, the heating units are thrown in series and the identified wire is now in the lower terminal, This circuit is shown in Figure 2, A . When the attachment lug is in the right-hand three-pole convenience receptacle, the Reating units are also in series and the identified wire is the upper terminal. In the right- and left-hand receptacles the right terminals are not connected. The identified terminal is the “roving terminal” because 1 and 2 are “hot” and it is desirable to know the location of the “hot” wire for safety. The three-wire cord lead from the heating unit to the control panel is a rubber-covered portable cord, the wires of which are covered with an identifying colored rubber. The colors used in these laboratories are white, red, and black. By accepted practice the white is the identified wire. To simplify or standardize the wiring, the term “red-top, black-bottom” is used. The red wire connects to the control terminal for the top heating udit and the black wire connects to the control terminal for the bottom
223
-2control panel more suited for general laboratory utility is the same as described but has two additional two-pole convenience outlet receptacles (Figure 3). These polarized receptacles are used with the identified wire a t the bottom. This panel may be used with any two heating eletnents having a common lead, utilizing the elements either in series or parallel. I n addition it may be used for the control o f a single unit heater equipped with a two-wire portable cord. These twopole receptacles may be used for heat control of small fractionating columns, laboratory heaters, hot plates, and boiling point apparatus.
\
G? /
yk-’ ,=\
1‘+-’I I
WY
, ! g Four-Pole Convenience Recap ta c 1 e,
FIGVRE 4. SCHEMATIC WIRISGI)IA(:RA>I
($> Two-Pole
Convenience. Receptacle - b \ arized
The construction of a 20-foot all-glass column with a threeelement jacket heating unit and the development of the pot heat-input control (1) necessitated the use of a control panel with three polarized autotransformers. The schematic wiring diagram for this panel is shown in Figure 4. The same connection conventions were followed as in the previous figures. This arrangement gives a maximum of utility without adding so many convenience outlet receptacles as to cause confusion. The addition of tJvo-pole outlets for autotransformers VI and IT2was contemplated, but rejected because of the excessive number of outlets.
FIGURE 3. SCHEMATIC F I R I N G DIAGRAM
heating unit. The white wire connects to the terminal of the common lead. The same color scheme is used in wiring the panel: black wire for the left autotransformer, red wire for the right, and white for the identified wires. To wire the attachment plug, the plug is held with the prongs toward the operator and the identified terminal to the right. The red wire connects to the top and the black t o the bottom terminals. To secure the maximum utility from a control panel it should be adapted to general laboratory work; there must be a uniformity in the construction of the units and a uniformity in the wiring attachment plugs. If one knows the color of the wire attached to heating units connected in parallel, the autotransformer that controls each unit is automatically known. This saves time and assures the proper control where desired.
Sfed
I
r
FIGURE 5. DEVELOPED VIEWOF Box
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FIGURE6. Box ASSEMBLED, SEAMS WELDED This panel may be used for the control of two heating elements connected in parallel with the common lead by plugging in the middle threepole convenience receptacle, or the two left-hand autotransformers may be used independently with three- ole attachment plugs by plugging in the left-Rand and the right-hand three-pole convenience receptacles. The right-hand autotransformer cannot be used with a three-pole convenience receptacle but onl\ with a two-pole polarized attachment plug. The three autotransformers may be used on a three-circuit heating system with a common lead-that is, a star hookup-by using a fourole attachment plug and the four-pole convenience receptacle fvhen an autotransformer is used to control a heating element from one convenience receptacle, it cannot be used for the control of another heating element from another of the convenience receptacles-that is, the middle autotransformer cannot be used to control a heating element from terminal 2 from the middle three-pole convenience receptacle and also a heating element from the right-hand three-pole convenience receptacle. The panels in these laboratories are made of 16-gage black iron. Wood may be used, but it is not recommended because of fire hazards present where fractionating equipment, boiling point apparatus, etc., are used. The developed view of the panel for the hookup shown in Figure 3 is shown in Figure 5 . The iron is bent along the dotted lines and seam-welded into the assembled box (Figure 6). The photograph of this finished panel is shown in Figure 7 .
Discussion The control panels as described should meet the needs for heat control in practically all cases encountered in the laboratory. Three autotransformers are the maximum that may be
FIGURE 7. PHOTOGRAPH OF FIKISHED PAKEL built into a portable panel without making it cumbersome and heavy. However, there is no reason why four, five, or six instruments cannot be connected to give the maximum utility by elaborating the diagrams as given. The autotransformer allows the jacket temperatures of fractionating columns to be adjusted a t any temperature desired to within the precision of the jacket thermometers (0" to 360" C.) or thermocouple potentiometer. I n well-insulated apparatus the rate of boiling of solvents has been adjusted to within 1 per cent of the desired rate in terms of drops per minute or milliliters per hour. I n the evenings when the voltage is constant the rate has been adjusted to within 0.5 per cent. Acknowledgment
The author wishes to acknowledge the assistance of Wallace Kinser and Otto Dickey, Electrical Engineering Department] in developing the heat control panel. Literature Cited (1) Morey, G. H., ISD. ENG.CHEM.,.4nal. Ed., 10, 531 (1938). PRESENTED before the Division of Physical and Inorganic Chemistry a t the 08th Meeting of the American Chemical Society Boston. Mass.
Removal of Adhered Rubber Stoppers
I
N T H E Analytical Edition of INDUSTRIAL ASD EKGIXEER- drop or tn-o of water is introduced between the glass and the rubber at the point of insertion of the file, the subsequent ING CHEMISTRY for January 15, 1940 (page 5 2 ) , there apremoval of the stopper is very greatly facilitated. peared a note by A. J. Bailey on the removal of adhered rubber F. A. Robinson, Glaxo Laboratories, Ltd., Greenford, stoppers. Shortly thereafter two readers called our attenMiddlesex, England, states that the tion to the similarity between this note and one by Lynn D. method is not without risk to the therWilson which appeared in the Sovember, 1939, issue of the mometer, \Thereas the following method Chemist-Analyst. is even simpler and there is little risk of It has been ascertained that hfr. Wilson's note reached the accident : Chemist-Analyst some months before bfr. Bailey's note was received here, but, as pointed out in the latter, i t seemed Moisten with glycerol or sodium hydroxide inevitable t h a t this method had been known and used. Rfr. solution the end of a cork borer slightly larger Bailey merely wished to emphasize its unusual effectiveness in diameter than the thermometer or tubing to be removed. Slide the cork borer over and the motive in publishing the note was to make it generally the end of the latter and rotate it slowly available to chemists] since i t had served the author and his while applying gentle pressure. The rubber fellow research men so satisfactorily. is forced away from the glass in preference It is unfortunate that neither Mr. Bailey nor any of those t o being cut through by the cork borer, which gradually passes through the hole in the through whose hands the note passed saw the previously pubstopper, leaving the thermometer free. I t lished note by Mr. Wilson. may be necessary to apply fresh lubricant hl. Parkin of the University of Sheffield, England, advises t o the cork borer from time to time. The us that he has used the method for 20 years and that if a accompanying diagram illustrates the idea.
