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Picture of the Week

LUX dark matter detector

Detecting dark matter

The kind of matter and energy we can see and touch – whether it is in the form of atoms and molecules, or heat and light, only forms a tiny proportion of the content of the Universe, only about 5%. Over a quarter is dark matter, which is totally invisible but whose gravitational attraction can be detected; while over two thirds is dark energy, a force that pushes the Universe to expand ever faster.
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Mixing things up

14 October 2013

Mixing and grinding samples is important in many chemistry experiments, but is  time consuming and labour intensive when done by hand. Hasok Chang, in research carried out while he was Professor of History and Philosophy of Science at UCL, uncovered evidence of an experiment in the 18th century which involved four weeks of shaking, all done by hand.

Magnetic stirrer

Scientists today have it much easier, with a range of devices to help. The photo above shows a magnetic stirrer: a rotating magnetic field coming from the equipment makes a small metal stirring device spin rapidly in the flask above, and can keep the liquid moving indefinitely.

This magnetic stirrer is being used for undergraduate teaching in UCL's Turner Laboratory.

Another approach, below, is the roller-mixer.

Roller mixer
Roller mixer animation
Roller mixer in action

The grey cylinders roll and rock, and samples left in sealed containers get gently agitated. In the photo above, the apparatus is being used to grind up material: inside the sealed containers, scientists have put ball bearings, which slowly grind a sample to a fine powder over a period of hours or even days.

In this case, the equipment is being used by UCL's Clean Materials Technology Group, in order to make fine powders for use in catalytic applications.

Photo credit: O. Usher (UCL MAPS)

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Magnetic stirrer

Roller mixer

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Page last modified on 11 oct 13 12:03