for Heat-Sensitive critters - Part 2

by Jean-Marie Cavanihac, France


To test the 'refreshing power' of this device, I have made some experiments using the assembly shown left with an electronic thermometer attached. (An internal/external thermometer can be used for example, which you can to find everywhere (car accessories shop...) for less than $10).
The graph below shows temperature evolution with and without this device, plotted against observation time with a stereo microscope. Half a liter of 3°C water (with 3 little ice cubes) has been used with one drop/second flow rate. The first part of curve shows the temperature rise on slide without the device; it reaches 45°C in less than a quarter of an hour! In the second part, the device is used and water flow enabled; the temperature decreased to 14°C then increased slowly. A temperature of 25°C should have been reached more than an hour after. To demonstrate the device's efficiency, water flow was stopped at 50 min; temperature again increased rapidly (third part of the curve). 

Note 1: After 30 min, cold water (5°C) was added into upper bottle and its contents stirred, note temp. dip on graph. Stir water from time to time.

Note 2 : Efficiency of device is increased if you glue 2 wedges (2 mm thick) onto lower side of PVC ring, to prevent lower glass window touching microscope plate or frosted glass.

Note 3 : In my device, the tube diameter I have used is a little too narrow and flow rate is slowed down. Air tubing for aquarium, as specified in parts list, should work better.

You can experiment with other parameters; increased flow, more ice added, water stirred more frequently, insulated bottles with polystyrene foam.... 

A second experiment has been made with a compound microscope. The light bulb's heating effect is less important and, this time, the device can be used to decrease temperatures to slow the activity of some animals to observe them at leisure. Add two spoonfuls of sodium chloride into half a litre of water, put it into the chiller and make ice cubes with another half a liter of such water, using freezer. Then proceed as with fresh water; salted water/ice temperature reaches - 6 °C. (Don't use it for whisky!)

The graph below shows how it's easy to maintain a slide temperature of ca. 5°C, using salted water and two salted ice cubes in the higher bottle with a water supply temperature of - 5°C. The temperature in the bottle began to increase (red curve) as soon as all the ice had disappeared. But with a half liter bottle you have more than 45 minutes to work with your specimen at 5°C.

The device can also function in reverse i.e. you can use it to warm specimens using tepid water to accelerate some biological processes (or to wake up winter sleeping critters!).

Don't forget to rinse chamber after use with distilled water to avoid hard water or salt deposits.

NOTE: The thickness of assembly (PVC ring + glass plates) can prevent moving the condenser nearer slide if device is used on a compound microscope. Use ring of 6 mm thickness max. 

Another cheap device to complete your lab and to increase critters comfort!
Work in progress: I am working with an interesting electronic component called a 'PELTIER effect device'. It has a unique property; when powered by DC current, (12 V, 3 A) one side becomes hot but the opposite side becomes COLD. It's possible to obtain 0°C on this side but the heat must be dissipated from the other side by a large aluminum radiator (15 x 15 cm). It's difficult to place this assembly on the microscope stage and I am trying to adapt it.


So what do you think to this project Mrs Copepod ?


Comments to the author Comments to the author sent via our contacts page quoting page url plus : ('jcavanihac','')">Jean-Marie Cavanihac are welcomed.

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All drawings and photographs © Jean-Marie Cavanihac 2001

Published in the June 2001 edition of Micscape Magazine.

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