London, July 15 (IANS): Scientists are close to finding a way to re-define the kilogram in terms of a mathematical constant instead of being based on a cylinder.

The research has been done by a team of Italian scientists. They are close to finding a new definition of the kilo-based on Planck's constant, which represents the size of the quanta in quantum physics and is as reliable as a mathematical constant as the speed of light in a vacuum, the Independent reported on Wednesday.

However, in order to do this they devised a way of estimating yet another constant, called Avogadro's number, which is the number of discreet particles - molecules or atoms - in a "mole" of substance.

A mole of water, for instance, is just a few teaspoons in volume but it contains approximately 6.002 by 10 to the power of 23 (10 with 23 zeros after it) molecules - Avogadro's number - which is greater than the number of grains of sand in the world.

Giovanni Mana and colleagues of Italy's National Institute of Metrology Research in Turin city of Italy have obtained what they believe to be the most accurate estimate of Avogadro's number to date, which would now be used to quantify Planck's constant and hence, help to re-define the kilogram in purely mathematical terms.

The present definition of a kilogram goes back to more than 125 years when a high-grade metal solid cylinder of platinum-iridium alloy was agreed to weigh precisely one kilo was locked in a vault in France at the Internatinal Bureau of Weights and Measures in Sevres.

The standard kilo, known as the International Prototype Kilogram, was reported losing weight for some unexplained reason, probably related to the loss of gas locked inside it when the cylinder was made.

As a result, scientists are no longer satisfied that this physical object is accurate enough of such a fundamental measurement and want to re-define it by 2018 in terms of a mathematical constant.