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V O L U M E 26, N O . 10, O C T O B E R 1 9 5 4 direct current, 145 r.p.m., driving through a worm gear reduction. (Both Type 5069230 and Type 5069600 are advertised by companies dealing in war surplus aircraft equipment.) The speed 1s adjusted to the sample to be evaporated by means of a multiple tap transformer and the circuit is designed to allow the elevator to be lowered faster than it ascends. A Powerstat or Variac, plus a fixed voltage transformer, may be substituted for the multiple tap transformer. A knob, a t the back of the unit, is attached to a spring-loaded clutch; this overrides the motor and can be used to raise the elevator part'ially when smaller quantities of liquid are to be evaporated. The heater is made from the element of a standard 600-watt coil heater which is formed into four separate coils in series-one for each tube-and then set into a Transite block. This type of heater was selected because it would not overload a standard 15ampere circuit. A thin stainless sheet surrounds the block to serve the double purpose of draft shield and reflector. A Variac in the line, set a t about 100 volts, controls the heater voltage. The tube rack supports the samples while they are drawn through the heater coils. It is attached t o a rod 0.5 inch in diameter that is guided in its travel by two linear ball bearings. l\licroswitzcheslimit t.he travel of the rack as well as terminate the cycle. A control box houses the transformer, a rectifier, and the timedelay switch. Both the motor and heater circuits are individually fused. One switch controle both circuits; however, a momentary contact switch must be depressed to override the low limit of the elevator. Pilot lights indicate the closing of both circuits and the direction of travel of the elevator (Figure 3). As the control box is separate from the evaporator, hazardous Polutions may be evaporated by remote cont,rol. ACKNOW LEDGhIENT
The surface evaporator was designed with the engineering assistance of R. A. Blomgren and N. J. G. Bohlin. F. J. Piotroxski designed and assembled the electrical circuit. The design layout and drawing were done by W. J. Fromm, Armour Research Foundation, Chicago, Ill.
The water, after passing through the lamp cooling jacket, enters copper tube A , issues from orifice B, travels vertically, and strikes brass contact C. The resulting contact allows current to flow between the grounding connection, E, and electrical contact C. An electronic relay, having a very low current requirement, is activated. The relay then closes the hydrogen lamp power supply circuit. When the coolant ceases to flow, the ground connection between E and C is broken, causing the relay to open the power supply circuit. Various simple relay circuits found in electronic publications can be used. In this case, the relay was a Central Scientific Co. electronic relay No. 99780 which was altered so that grounding the relay post would close the circuit of the hydrogen lamp power supply. The unit described has been in use for over a year now and has required cleaning of the relay contacts only once and replacement of a burned-out vacuum tube. If any surface coating develops because of salts or slime formation, this should be cleaned from the tube. .\ coating of a waterrepellent material is applied orrasionnlly. Thermal Circuit Breaker for Water-cooled Systems. Sidney Solorray' and Frank J. Rennie, Division of Sutrition and Physiology, Public Health Research Institute of the City of Yew York, Inc., New York, ?i. P. of normal operations in a chemical laboratory, 1 reliance ' course must often be placed upon a continuous supply of cold N THE
water. TKO types of failure have been encountered. The water supply may be interrupted because of fall in pressure or swelling of washers or the temperature of the tap water may rise as a result of decreased use of water a t remote points. In either event, if the water is being used to cool a reflux condenser over a low-boiling solvent, the solvent may be lost and the solute damaged by heat
Control to Protect Against Damage by Interruption of Cooling Water Flow. Don H. Snderson and Richard G. Smith, Industrial Laboratory, Eastman Kodak Co., Rochester 4, N. Y.
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hydrogen lamp of a Cary recording spectrophotometer needs protection against damage caused by overheating resulting from interruption of the flow of cooling water through the jacket of the lamp envelope. Other apparatus also requires protection against interruption of flow of cooling water. Many designs have been published for flow switches which are pressure operated. They have been used to control water flow successfully in many instances. If c o r r o s i o n products or other materials arc prevented from plugging the exit line, switches of this type can be reliable. However, inadequate maintenance and cleaning which allowed plugging of water lines on the outlet side of the switch would result in failure of the safety switch to operate even if the water flow ceased completely. A solution to this difficulty Figure 1. Safety Flow was secured by arrangSwitch ing a switch t h a t A . Copper tube o p e r a t e s o n l y when E . Orifice C. Brass contact water is actually flowD . Wire t o relay ing. T h e essential E . Wire t o ground F . Positioning screws features are shown in G. Plastic tube, !bout 1.5 inches in Figure 1. diameter, m t h plastic cap
mT
WI
HE
U
......... HC
Figure 1. Brass Water Chamber WI. Water inlet FS. F e n a d s w i t c h WO. Water outlet
W C . Water chamber
HC. Heating coil T.
Thermometer
To insure against such damage, a thermally controlled circuit breaker has been designed which interrupts the power t o any electrical device, such as a hot plate, whenever the water supply fails or whenever its temperature exceeds a preset value. The water discharge from the chemical equipment enters a brass water chamber (Figure 1) via an inlet tube, W I , and drains into the sink via an outlet, WO, flowing past a thermometer. Inserted into the water chamber is a Thermoswitch (Catalog No. 17100, Fenwal, Inc., Ashland, Mass.), which is normally closed but opens upon rise of temperature. The opening temperature is readily adjusted by a setscrew. A heating coil of 126 turns of No. 27 Nichrome wire, between layers of asbestos paper, surrounds the water chamber. 1
Present address, Schlumberger Well Surveying Corp., Ridgefield, Coon.
