On Wed, 2008-05-21 at 16:28 +0200, Daniel Carrera wrote: > Ian Lynch wrote: > >> this is agreed to be unsatisfactory, > > > > Yes it would be difficult to see how the measurement might be checked > > without losing the odd atom or two :-) > > Wikpedia says that the lump of metal gains mass because it absorbs > atmospheric contamination.
You definitely don't want anything that oxidises too easily. Adding oxygen atoms will definitely increase the mass. Store in a vacuum but then that is not then easy to get at and it's impossible to achieve a perfect vacuum. > So they have this complicated technique to > clean it, and the technique removes about 5-60 micrograms of > contaminants. I imagine that you have to worry about not removing too > much stuff every time you clean it. > > They actually have several replicas around the world, for mutual > calibration. But it turns out that these masses have been diverging from > each other. The base prototype (the one that truly defines the Kg) has > lost about 50 micrograms in its life compared to the replicas. Nobody > knows why. So they also don't know whether the main prototype has lost > mass or whether the replicas have gained mass (maybe they replicas don't > get cleaned as well?). And of course, it's possible that they are all > diverging one way or the other, and we wouldn't know. > > There is an additional 30 microgram monthly variation in the proptotypes > which is not explained either. > > Daniel. > > --------------------------------------------------------------------- > To unsubscribe, e-mail: [EMAIL PROTECTED] > For additional commands, e-mail: [EMAIL PROTECTED] > -- New QCA Accredited IT Qualifications www.theINGOTs.org You have received this email from the following company: The Learning Machine Limited, Reg Office, 36 Ashby Road, Tamworth, Staffordshire, B79 8AQ. Reg No: 05560797, Registered in England and Wales. --------------------------------------------------------------------- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
