WHAT happens when a teabag is placed in a cup of hotwater? The colour of tea immediately diffuses into the hot water. But when the same experiment is tried in a cup of cold water, the colour change is significantly slower. Now, a Russian scientist, Vithold Bakhir, has demon- strated a technique through which the colour from a teabag diffuses faster in a sample of cold water than in hot water. Researchers believe that the device invented by Bakhir holds the promise for a new and economical method for procuring potable water from a dubious supply source (Appropriate Technology, Vol 2 1, No 1).

The device consists of 3 chambers containing different metallic catalysts which manipulate the important chemical variable -- redox potential. Redox reactions are those where chemical processes called reduction and oxidation take place. Reduction means the loss or removal of oxygen from, or the addition.of hydrogen, to an atom or molecule while oxidation is the reverse process.

The catalysts raise the redox potential of water to a high positive value, then quickly subject it to a high negative value. The sudden change in the redox potential breaks up various microorr and thresher. t for small cultivators, this iking mini-tractor has a 6 ed on a sturdy steel chassis fabrited for the purpose. Costing a oderate Rs 37,000, Mech Bull is kable for assembly and repairs by ganisms, viruses, bacteria and other large organic structures into small harmless molecules.

The water which emerges after being subjected to this process is completely sterile, and has a lower redox potential than the normal drinking water - quite similar to water inside the human cells. Bakhir says @hat the water purification device can be produced in different sizes and versions. "But even the smallest model can produce several litres of potable water per minute, and much faster than a filter jug. No chemicals are necessary. It does require electricity but only 5 watts - far less than an ultraviolet purification unit", adds Bakhir.