Monthly Archives: March 2015
On 27th March 1923, James Dewar, the Scottish chemist and physicist died. He is probably best known for his invention of the Dewar Flask which he used in conjunction with extensive research into the liquefaction of gases. He was also particularly interested in atomic and molecular spectroscopy, working in these fields for more than 25 years.
|(20 September 1842 – 27 March 1923)|
By 1891 James Dewar had designed and built machinery which yielded liquid oxygen in industrial quantities. Around 1892 the idea occurred to him of using vacuum-jacketed vessels for the storage of liquid gases – the Dewar flask (otherwise known as a Thermos or vacuum flask) – the invention for which he became most famous. The vacuum flask was so efficient at keeping heat out that it was found possible to preserve the liquids for comparatively long periods, making examination of their optical properties possible. Dewar did not profit from the widespread adoption of his vacuum flask – he lost a court case against Thermos concerning the patent for his invention. While Dewar was recognised as the inventor, because he did not patent his invention there was no way to stop Thermos from using the design.
The vacuum flask consists of two flasks, placed one inside the other and joined at the neck. The gap between the two flasks is partially evacuated of air, creating a near-vacuum which prevents heat transfer by conduction or convection. Vacuum flasks are used domestically to keep beverages hot or cold for extended periods of time and for many purposes in industry.
Various sizes of Dewar flask are available and are commonly used in Cryogenics for the storage of tissue samples for example. See also, the safe use of liquid nitrogen by clicking here.
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Copper (II) sulfate, also known as cupric sulfate or copper sulphate, is the chemical compound with the chemical formula CuSO4. This salt exists as a series of compounds that differ in their degree of hydration. The anhydrous form is a pale green or grey-white powder, whereas the pentahydrate (CuSO4·5H2O), the most commonly encountered salt, is bright blue.
|Copper Sulphate Crystals|
Copper sulphate is normally produced industrially by treating copper metal with hot concentrated sulphuric acid. Laboratories generally purchase their own – eg here.
At 650 °C (1,202 °F), copper (II) sulphate decomposes into copper (II) oxide (CuO) and sulphur trioxide (SO3). Its blue colour is due to water of hydration. When heated in an open flame the crystals are dehydrated and turn greyish-white.
Several chemical tests utilize copper sulphate. It is used in Fehling’s solution and Benedict’s solution to test for reducing sugars, which reduce the soluble blue copper(II) sulphate to insoluble red copper(I) oxide. Copper(II) sulphate is also used in the Biuret reagent to test for proteins.
Copper sulphate is a commonly included chemical in children’s chemistry sets and is often used to grow crystals as can be seen here.
The chemical is also used in flame tests – again which can be seen here.
In 2008, the artist Roger Hiorns filled an abandoned waterproofed council flat in London with 75,000 litres of copper sulphate solution. The solution was left to crystallize for several weeks before the flat was drained, leaving crystal-covered walls, floors and ceilings. The work is titled Seizure.
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Ever wondered what the smell of the earth is? Maybe you’ve visited the countryside while farmers have been ploughing their fields and smelled it. The smell is caused by Geosmin which is an organic compound with a distinct earthy aroma produced by a type of Actinobacteria.
Geosmin is produced by the bacteria Streptomyces, a genus of Actinobacteria and released when these microorganisms die.
Geosmin is a colourless liquid, with a boiling point of 270°C. The human nose is extremely sensitive to geosmin and is able to detect it at concentrations as low as 5 parts per trillion. It is the smell after a rainstorm when the ground is wet.
Geosmin is often responsible for unpleasant tastes in water supplies. Cyanobacteria (blue-green algae) and actinobacteria release geosmin when they die, and this can be absorbed by bottom-feeding freshwater fish such as carp and catfish. Geosmin combines with 2-methylisoborneol, which concentrates in the fatty skin and dark muscle tissues. Geosmin breaks down in acid conditions; hence, vinegar, lemon and other acidic ingredients are used in fish recipes to help reduce the muddy flavour.
Geosmin can sometimes be tasted in wine or drinking water.
It has also been suggested that camels can detect the smell of geosmin that had been released by Streptomyces miles away in wet ground, and track the geosmin to find an oasis; in return the camel could carry away and disperse the spores of the Streptomyces bacterium.
Soil is considered to be the “skin of the earth” and consists of a solid phase (minerals and organic matter) as well as a porous phase that holds gases and water. It carries essential nutrients for plantlife and is a habitat for organisms that take part in decomposition of organic matter and the creation of a habitat for new organisms.
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