edited by DENNISSIEVERS
Inventory Control Homemade Sand Bath Dennis Slevers Central High Schwl Breere. IL 62230
A large number of experiments in chemistry and biology call for the slow evaporation of a solvent. For most of these experiments, a low flame on a Bunsen burner or a lowtemperature hot plate is employed. While acceptable, some splattering, and therefore error, is introduced into the experiment. An inexpensive, easily made alternative is the sand bath. A shallow metal pan is constructed from 18 gauge galvanized sheet metal. Figure 1gives some approximate dimensions for the pan. All corners should he spot-welded and soldered for streneth and to ensure a tieht fit. If shoo facili" ties for constructing such a pan are not available, a large rectangular aluminum cake pan can be substituted. The dimensions are not critical but the tray should allow adequate room for the heat tape being used. Heat is provided by a modified heat tape, of the type used to prevent freezing of water pipes, and is available from most hardware stores. A 6-ft tape is suitable for the pan shown in Figure 1. To modify the heat tape, open the shield around the thermostat, remove the ac line from the thermostat in-
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Central Community High School Route 50 West Breese. IL 62230
put and connect to a dimmer switch similar to that used to control room lights. The output of the dimmer is connected to the output side of the thermostat. Figure 2 is a schematic diagram of the needed changes. The purpose of the dimmer is to h v ~ a s the s thermostat as the shutoff ooint is too low. There little danger of damage to any component in this arrangement because the current is generally less than or equal to that used in normal operation. I have used these devices in continual operation for periods of up to six days without any problems. The modified tape is then installed in the pan on its side. This is most easily accomplished by placing 2-3 cm of white sand (ash tray sand from maintenance supply houses is recommended) in the Dan and arraneine the tane as shown in Figure 1.The edgekise placemeG 2 the tape is preferred because it allows for more uniform distribution of heat. Once positioned, sand is added to a total depth of 6 7 cm. A piece of masonite or olvwood can be laced under the Dan to protect counter io& but is not essential because temperatures are not excessive. When romplewd, thermometers should be placed at different locations and the dimmer control calibrated for wecific temperatures. The units I have built provide a range from ambient to 60 O C . The temperatures are fairly uniform if the tape is evenly spaced. By using larger tapes, smaller pans, or multiple heat tapes, the temperature range can be set to any level desired.
A Low-Cost Conductivity Apparatus Thomas Russo MillbwurnHS 434 Miliburn Ave. Millburn, NJ 07041
When discussing the general properties of elements, compounds, and mixtures, one criterion used in characterization is that of electrical conduction. The property of matter to conduct or not to conduct electrons is basic to the concept of metal/nonmetal behavior and of ionic versus covalent solutions. Pronerties of weak or strone acids and bases are directly dependent on ionization. The conduction of electricity bv matter. whether i t he in elemental f o m or in ionic solut:ons, is therefore a valuable tool in the characterization of matter. This aspect of matter is usually demonstrated by expen-
Figure 1. The sand bath setup.
Wiring Modification
AC Line
Thermostat
Cu ( bare wire
u Figure 2. Wiring madiflcation.
Schematic of apparatus
Volume 63
Number 11
November 1986
981
sive devices such as a volt-ohm meter or conductivity apparatus that costs anywhere between $50 and $100. An inexpensive alternativeis suggested by this article. The parts for this device can he obtained quite readily from any Radio Shack store for under $4.00. The major cost for the probe is the 9-V battery that serves as the power supply. The battery should last for at least two years since the power requirements for the probe are quite small. A set of apparatus can be fabricated for an entire class of 20 (10 groups of 2) for under $30. The parts list follows. PBR NO.
276-0366 271-1321
... ...
DBSniptlon
FTioe
Blinking red LED (COX21) I-Kahm resistor ( I of 5) 9 V battery clip (1 of 5) 9 V battery
$1.29 0.08 0.20 1.29 $2.86
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The circuit can be built according to the schematic (see figure) and housed in a soda straw or empty ball-point-pen housing. Bare copper connecting wires serve as electrodes. When the circuit is used to test a solid or a solution, the
982
Journal of Chemical Education
LED will elow or blink in response to the conductivity of the substance-under test. ~ i n i m aamounts l of solution 61 solid are reauired for the testing procedure. The copper wires are placedin or on the subst&ce under test and~theoutput of the LED is noted. The followin~are results of an experimental run: SolUtim
LED Response
Solid
2 MHCl 2 M NaOH 1 MAcetic Acid Distilled water Ethanol Toluene
flashing fleshing glowing dull glow dull glow no glow
Stainless steel spoon Copper wire Sample of Si Sample of AS Leaded glass Plastic fork
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This simole anoaratus can also be used as an indicator for stoichiometric titrations such as the barium hydroxide and sulfuric acid titration. The minimal glow of the LED when used in this application serves as a titration endpoint indicator. Readers are invited to use this simde, cheap, and aualitative device to further students' und&s&ndingof conduction of elements and ionization of compounds. ~
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