No, you're not losing weight: the kilogram is getting heavier

The next time you feel you gained weight, you might want to weigh yourself in kilograms.

 

The reason? Experts say the International Prototype Kilogram (IPK) —a small bar of platinum used to represent the standard unit for kilogram weight— has gotten heavier since its introduction in 1875.

 

"If the kilogram does put on weight then it's imperative that we understand exactly how the IPK is changing," said Professor Peter Cumpson, according to a report on UK's The Telegraph.

 

Experts from the University of Newcastle were quoted as saying industrialization and modern living may have taken their toll, and contaminants built up on the surfaces, thus increasing their weight.

 

But this may only amount to a weight gain of only tens of micrograms in the past 137 years.

 

Originally, the IPK is a matchbox-sized piece of platinum stored in the International Bureau of Weights and Measures in Paris.

 

In 1884, 40 official replicas were made and distributed around the world to standardize mass. The UK holds replica 18 at the National Physical Laboratory (NPL).

 

On the other hand, The Telegraph said the researchers believe each of the replicas may have gained slightly different weights.

 

XPS machine

 

Professor Cumpson and Dr. Naoko Sano used a Theta-probe X-ray Photoelectron Spectroscopy (XPS) machine to analyze surfaces similar to the standard kilogram.

 

They assessed the likely build-up of hydrocarbons and also pondered how best to remove them, reports the  Journal of Metrologia.

 

Cumpson and Sano found that a "suntan" of ultraviolet and ozone helped return them to their original mass.

 

"Statute decrees the IPK is the kilogram. 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," Cumpson said.

 

Cumpson also said the IPK and its 40 replicas worldwide are all growing at different rates, diverging from the original.

 

"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 overindulgence never happened," he said.

 

"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. There are cases of international trade in high-value materials – or waste – where every last microgram must be accounted for," he added.

 

'Suntan' to the rescue

 

Cumpson said what they have done at Newcastle is effectively give these surfaces a suntan.

 

"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," he said.

 

Alternative to weight measurement

 

Meanwhile, efforts are under way in several National Measurement Institutes to find an alternative to the IPK.

 

These alternatives offer a standardized value for the kilogram that is not based on a matchbox-sized piece of metal.

 

But until then, the prototype kilograms are what the world relies on for its mass scale, The Telegraph said.

 

"If the kilogram does put on weight then it's imperative that we understand exactly how the IPK is changing," said Cumpson.

 

He added it was the cutting edge technology which had allowed the team to make their calculations.

 

"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. Rather like an MRI scanner, it takes a cross section of the material but at an atomic level," he said.

 

The second part of the machine is the Argon cluster ion gun which fires charged droplets, each containing about a thousand Argon atoms.

 

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