When calibration ha. been completed, remove and replace the reference voltage source with the sensor, and reconnect the resistor R7 to the circuit. Figure 2 shows one of the thermometers we have built. It has been in use for teaching for more than three years and students have not encountered any difficulties in operation. Our students have found it very simple to calibrate and they prefer using this electronic thermometer to the classical Beckmann thermometer. It takes an average student less than 3 min to learn how to calibrate it and use it for temperature measurement. The self-heating rate of the sensor is 0.002 w. For most thermochemical experiments designed for teaching, the heating effect is insignificant compared with the amount of heat generated when the total volume of solutions involved is larger than 100 mL. However, for very accurate measurements, a small correction factor may be necessary. We have used this device to measure the cooling and heating characteristics of solution and thermometric titrations. Coupled with aproportional controller, i t has been used successfully as temperature controller for thermostats and heating mantles for unattended distillation experiments. Llferafure Cited (11 Ferguson,A. M., and Phillips, L. F., J. CHEM. EDuC.,50,684 (19731.
(2) "Linear Data Bmk." National Semimndu*,
corporation,29W Spmimndudor Drive. (19821.
SsntaCiara. CA 9SoSI. (3) Warner, B.D.,Boehine.G.,sndPool,C.H..J.CHEM. EDUC.,59,65
Figure 2. The completed thermometer. readily available in most electronic components shups such as Radio Shack or those mentiuned hv Warner and associates (3).Excluding the cost of the meter, the total cost is about $50. Anyone with some basic knowledge of electronics will spend no more than five hours to assemble it. Calibratlon Procedures T h e following steps should he carried out in sequence. The Sensor 1) Immerse the sensor assembly in an ice water bath. 2) Set R8 to get +2.730 V across the sensor leads.
The Fixed Voltage Generator (A3) 3) Disconnect one end of R7. 4) Replace tbe sensor with a variable voltage source, adjust this
voltaee to read +2.730 V. 5) 3wil;h S\W should he0-100T setting. 6) Adjust H 2 5 . i ~lhat pin fi of ( A I J is0 V. The Variable Voltage Generator (A2) 7) Switches SW2 and SW3 are at 10DCposition.
8) Set 10 turn potentiometer R19 at 0000 position. 9) Adjust R11 to make pin 6 of (Al) read 0 V. 10) Increase the voltage reference source to 2.830 V. 11) Set 10-turn potentiometer R19 to 1000 position. 12) Adjust R20 to make pin 6 of (Al) read 0 V (for differential of 10°Cmeasurement,only the low-end setting with R11 requires adjustment, R20 is for initial calihrstion only.) Output Meter
13) Set 10-tornpotentiometer R19 to 0000 position. 14) Adjust meter resistor R17 to get a full scale deflection
Inexpensive Ring Holders for Round-Bottomed Flasks Jonathan H. Moffetf, Laurence Poncini, a n d Franz L. Wimmer S c b l of Natural Resources University 01 the South Pacific P.O. Box 1168
Suva. Fuji
I n the laboratory there is the perennial problem of placing round-bottomed flasks onto flat surfaces. The usual solution is a cork ring on which the flask is seated. These cork rings are hulkv. awkward to store. and susce~tihle to deterioration bv they are too large fo; r e a d s absorbing chemicals. flasks smaller than 50 cm3 capacity and are relatively expeusive. In desperation, a beaker is often used as a makeshift holder, or the flask is clamped to a retort stand. The Iint~ermethod is tlifficult witha hot flask. Both methodsare makeshitt, present storage problems, and tie up valuable equipment. w e have found the following holders to be useful for supporting round-bottomed flasks of any size' a t a very low cost.
oreo over,
Plastic Lids (suitable for flasks from 25 to 500 cm3 capacity). The plastic lids found on jars have a variety of sizes and i t is quite easy to find ones that are suitable. Small pieces of rubber tubing are split lengthwise and slipped onto the edge of the lid. I t is not necessary for the tubing to go completely around the circumference since it is just as effective to use three short lengths placed 120' apart (as shown in the photograph). This uses less tubing, is easier to make, and the tubing is less likely to peel off. Both ordinary and thick-walled pressure-tubing were used, with the latter being less likely to slip off. For permanency, the tubing can he glued in place.
Variable Gah Amplifier ( A l )
15) Switch SW2 at 1°C position. 16) Decrease voltage reference to +2.740 V. 17) Adjust R2 to get a full scale reading on the meter.
388
Journal of Chemical Education
'
There is still a problem with very small flasks (i.e.. 5 and 10 cm3) due to their high center of gravity. They are best stored in the rubber sleeves used with Gooch crucibles.
is virtually eliminated if "useless" short lengths of tubing are used. While cork may withstand higher temperatures than rubber, very hot flasks should never be placed on either type of ring.
Reducing Funnel Breakage Gary Sprague MBdford Senior High Schwl Medlord, OR 97504
We have found the followingimprovisation helpful in preventing breakage of long-stem glass funnels in our chemistry labs. Since most of the hreakage occurs when funnels fall over onto a table top, we looked for a way to eliminate the shock of the stem when it hits. This was accomplished by placing a short length (1 em) of latex tuhing, 31s-in. inside diameter, 'Ia-in. wall thickness, on the end of the stem. Actually, the tubing size is not critical so long as i t fits the stem, is thick enough to absorb the shock, and prevents hreakage. The tuhing is positioned on the stem without covering the tip so that the tubing does not become contaminated with chemicals during funnel usage.
selection of flask holders made from (clockwisefrom bottom left) plastic lids, rubber tubing, and a polyethylene bonle. Figure 1 . A
Toroldal Flask Holderss Tublng
Typea T T
P P
P P
P P
,anglh (em) 12-13 13.5 15 17 20 23 27 30
inside Diameter ol Term (cml
Capac;ly ol FlashC (dm3)
triangle lriangle
0.01 0.025 0.05. (0.1) 0.1. (0.25) 0.25. 0.5 0.5, 1, (2) 1.2. (5)
3.5 4.5 5 6 7 8
9 5
'Small flasks (50.025dmS)are top hsavy due to t h l r high center of gravify. = thln-wailed (outside diameter = 1.0 cmJ: P = pressure (outside diameter = 1.4
cm).
ParenVUIsas indlsato an ananate nadk size mat may be wed with me ring size.
Plastic Bottles (suitahle for flasks from 25 to 500 cm3 capacity). Old plastic bottles may he utilized by slicing them into sections (as shown in the Figure). The height of each section depends on the diameter of the bottle, the rigidity of the ~lastic.and the size of flask to be sunnorted. A straight cut was bhtainid by using a ruhher handas a guiding mark. Short lengths of ruhher tubing- were added (as shown in the ~ h o t o graph). Rubber Tubing (suitahle for flasks up to 20 dm3 capacity). This was found to be the quickest and most effective method. A suitahle length of rubber (preferably pressure) tubing (see Table) is cut and the ends joined. A variety of connectors can he used. The best tvDe is a tube with enough .. rigiditv .. . to be pushed inw ruhher'khing hut still flexible enough ro Iwnd slirhtlv. Thr t t ~ t n !froma rhstic wash hottlr isa cowl exsrn~le. ~ i torus2 e thus formed provides a non-slip &face and also cushions a flask when i t is put down. Such a rine (internal diameter 15.5 cm) formed from 2-cm tuhing can support a 20dm3 flask at all angles. The cost of these rings was found to he approximately one-third the price of the corresponding cork rings. This cost
F a very small flasks(525 cm3)the torus is shaped intoa triangle. The flaskscan be suppwted only wilh the neck vertical due to their high
la) funnel.lb) bumDer made from latex Funnel with rubber bumper: . . long-stem . tubing. (c)approximately % cm of stem remains exposed.
I I
This column reorasemsa consolidation of me ADDaratus Review and nllaltm Foghlers IeaNes um(l a wg1. e d m x ~ hp Reader9 w II continue to tono bsetui aspects of ban. mcld cq mrmds and deta b of how lhey can save money by building their own equipment, and information on and evaluations of currently available equipment, apparatus, and supplies. Novel, timesaving, or cost-saviag techniques also will be shared in this feature. Readers Interested in contributing to this feature should contact the feature editw.
center of gravity. Other flaskscan be supported at any angle.
Volume 61
Number 4
April 1984
389
