Category Archives: From the Lab

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The Kilogram turns 125

We all know what a kilogram is, right? It’s the mass of a bag of sugar. Thank goodness for the bag of sugar. Without it we’d be forced to imagine 1/7000th of an African bull elephant or 1/14560th of a double decker bus or God only knows what fraction of the weight of Wales.

Having a clear visualisation of the kilogram is important for all sorts of reasons, not least because it’s one of the seven SI units, the fundamental alphabet of symbols which can be combined in a variety of ways to express any physical quantity. Speed, for instance, is measured in metres per second, whereas force can be expressed in terms of kilogram metres per second squared.

The kilogram was accepted into this metrological pantheon alongside the metre 125 years ago today, when the value of both units was defined at the first General Conference on Weights and Measures organised by the BIPM. As a consequence of that meeting, three identical kilograms were cast by the firm Johnson Matthey out of a mass of platinum-iridium alloy. This alloy was chosen because of its density and chemical stability, meaning that the kilograms would be both small and resistant to rust. One of the kilograms was kept at the BIPM offices in Sevres, and two were sent for safekeeping in America. Rumours that a further three were subsequently distributed to the elven-kings under the sky have no foundation in truth.

One kilo to rule them all

One kilo to rule them all

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Liquid nitrogen bucket challenge

The inevitable Ice Bucket Challenge notification came along, courtesy of the Brothers Pag. Anyone who knows me knows that I can’t swim, so I wasn’t prepared to take the risk of attempting the challenge.

Also I didn’t have any ice in my lab, but I did have a Dewar of Liquid Nitrogen, so here is Balloon Matt nobly taking the challenge in aid of the DEC Syria crisis appeal.

**SAFETY NOTICE** Don’t do this at home. If you have liquid nitrogen at home, why on earth do you have liquid nitrogen at home? Whilst pouring and transporting liquid N2, heavy duty cold-proof gloves and a face visor must be worn. Do not touch parts of the balloon directly after they have been in liquid nitrogen. NEVER POUR LIQUID NITROGEN OVER YOUR OWN HEAD a million things can go wrong and you can lose eyes skin and hair: remember what happened to Boris. Do not cool an air filled balloon for prolonged periods due to risks of liquid oxygen condensation. **THANK YOU**

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