The Kilogram Has Been Putting On Weight
January 7, 2013

Scientists Say The Kilogram Has Been Putting On Weight

Brett Smith for - Your Universe Online

When getting on the bathroom scale after feasting at all the holiday parties, most of us have come to expect a larger number than usual — but scientists from University of Newcastle say that the kilogram itself has been bulking up over the years.

The original weight standard for the kilogram (about 2.1 lbs.) is known as the International Prototype Kilogram (IPK), and the British researchers say the series of platinum-based models for the kilogram have added tens of micrograms of hydrocarbon “pollution” since their creation in 1875, according to a new report in the journal Metrologia.

"It doesn't really matter what it weighs as long as we are all working to the same exact standard — the problem is there are slight differences,” said lead author Peter Cumpson, a professor at Newcastle University´s School of Mechanical and Systems Engineering. “Around the world, the IPK and its 40 replicas are all growing at different rates, diverging from the original.”

The original IPK is a small cube of platinum that is currently stored in the International Bureau of Weights and Measures in Paris. In 1884, forty replicas were created and shipped to governments around the world in order to standardize mass on the metric scale.

"We're only talking about a very small change — less than 100 micrograms — so, unfortunately, we can't all take a couple of kilograms off our weight and pretend the Christmas over-indulgence never happened,” he noted.

"But mass is such a fundamental unit that even this very small change is significant and the impact of a slight variation on a global scale is absolutely huge,” Cumpson continued. “There are cases of international trade in high-value materials — or waste — where every last microgram must be accounted for.”

Using a cutting-edge device known as Theta-probe XPS machine, Cumpson and his colleagues were able to calculate the exact weight of the models.

"The Theta probe allows us to look at the composition of very thin layers by measuring the angle at which the electrons emerge from it,” said Cumpson. "Rather like an MRI scanner, it takes a cross section of the material but at an atomic level."

A second function of the machine is an Argon ion gun that allows for the targeted analysis of the platinum standards.

"The Argon cluster ion gun allows us to analyze organic materials without damaging the inorganic surface, in this case the platinum alloy," Cumpson said.

According to their report, the scientists were also able to show that exposure to UV rays and ozone could effectively cleanse the models of their excess weight carbon-based weight.

"What we have done at Newcastle is effectively give these surfaces a suntan,” Cumpson said. “By exposing the surface to a mixture of UV and ozone we can remove the carbonaceous contamination and potentially bring prototype kilograms back to their ideal weight."

Officials are working to avoid the contamination problem in the future as many National Measurement Institutes are looking to replace the IPK. Until then, the match-box-sized kilograms will continue to be the world standard for mass.

Meanwhile, the Newcastle team announced that their next project will be to study the addition of atmospheric mercury to other the metallic standards.