My Science School

The Hopi Indians of south west America still trying to make rain by sacrificing Golden Eagles and dancing with live rattlesnakes in their teeth. But while they perform their traditional rain dances to please their gods and get rain for their crops, others have adopted a more scientific approach.

In 1946 Vincent Schaefer and Irving Langmuir started their work at the general electric research laboratories in Schenectady, New York, which proved that rain clouds could be artificially encouraged to produce showers.

Clouds are made up of billions of particles of water too small to fall as rain. Only when the droplets grow to a quarter of a millimetre or more will they fall as a fine drizzle. Smaller droplets evaporate before reaching the ground.

One way the droplets grow is by freezing to form particles of ice. In the cloud containing some ice particles and some water droplets, the ice particles grow rapidly as the droplets evaporate and the valour is transferred to the ice. Since the temperature of clouds is often below freezing it might be expected that the droplets would freeze easily. But the water can be 10 or 20° below freezing (supercooled) without actually freezing.

The reason for this is that the water in clouds is absolutely pure, without any dust or other contaminates which can from the centre of an ice crystal. If tiny particles are provided, the droplets freeze, grow quickly until they are large enough to fall, and then melt as the temperature rises, reaching the ground as rain.

Schaefer and Langmuir proved that small particles, usually of silver iodide, added to supercooled clouds could create rapidly growing ice crystals. These particles have been dropped from aircraft, carried by rockets or even released at ground level for air currents to carry them aloft.

In the Soviet union, 70 mm artillery guns have been used to fire silver iodide particles into clouds, exploding at the right height to disperse the chemical.

As long as the clouds are supercooled the technique may work increasing rainfall by up to a fifth. But since it is impossible to know how much rain could have fallen and anyway there are still question marks over the methods economic effectiveness.

 

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Acids can gradually wear away and destroy almost everything they touch. All are soluble in water, and their strength is measured by their potential of Hydrogen.

The potential of Hydrogen scale runs from 1 to 14. One is extremely acid, 7 is neutral, and 14 is very alkaline (the opposite of acid).

The potential of hydrogen content of a liquid is measured with a potential of Hydrogen metre or with Universal Indicator paper, such as litmus. A strong acid turns the indicator paper red, while a neutral liquid turns it green. Strong alkaline liquids turn the indicator purple.

 

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For most of the time when I was at school, a chemistry teacher would walk into our class and say “Uuu”. While the uninitiated ones were often trembling to find out if the “you” meant themselves, for the rest of us it was clear that our teacher was speaking about element 111.

It has now been 25 years since element number 111 in the periodic table, roentgenium, was discovered, during which a few more synthetic elements have been added to the table. For it was on December 8, 1994 that atoms of roentgenium were discovered and detected for the first time.

Bombard bismuth with nickel

As early as 1986, nuclear physicists at the Joint Institute of Nuclear Research at Dubna, Russia, bombard the element bismuth with nickel in the hopes of creating element 111. Alas, it wasn’t to be as they weren’t able to detect any atoms of a new element.

It had to wait another eight years before the discovery was eventually made. The methodology was similar, but the protagonists weren’t. As it was a group of scientists led by German physicists Peter Armbruster and Gottfred Munzenberg at the Gesellschaft fur Schwerionenforschung (GSI Helmholtz Centre for Heavy Ion Research) in Darmstadt, Germany who enjoyed the success. In fact, Armbruster and Munzenberg were involved in the discovery of every element from 107 to 112.

The experiment involved bombarding a target of bismuth with nickel ions in the hope that the nuclei of the two would fuse together to form a bigger atom, once the nickel penetrated the bismuth nucleus. The trick was to carefully control the energy of the collision in order to ensure that fusion did take place.

Getting it right

This was needed because if the nickel ions weren’t fast enough, they would move off bismuth on contact, unable to overcome the repulsion between two positive nuclei. If, however, the nickel had too much energy, then the compound nucleus would just fall apart owing to the excess energy. Considering that most of an atom is empty space, successful collisions weren’t easy.

The scientists observed three successful collisions on December 8, 1994, forming atoms of atomic number 111 and mass 272. The new atoms were identified based on what happened to them when they decayed.

Considering that the atoms formed were very short-lived-what with a half-life of 1.5 milliseconds – it was some effort on the part of the scientists to realise that they underwent successive alpha decay to form atoms of element 109, 107, 105 and 103.

Uuu is for unununium

Even though the discovery was announced in a paper published in 1995 and further experiments conducted in 2000 by the discoveries yielded a few more atoms whose decay chains could be traced up to element 101, element 111 was given only a temporary name. This was because the permanent name had to wait until independent confirmation of its existence was provided.

The temporary name, as dictated by the International Union of Pure and Applied Chemistry (IUPAC), was derived from the atomic number. Element number 111 was therefore called unununium and was given the symbol Uuu (the “Uuu” in the first paragraph now makes sense, doesn’t it?).

A team of scientists at the RIKEN Linear Accelerator facility in Japan were able to make a few atoms of element 111 in 2003, providing the independent confirmation. Those in Darmstadt were given the opportunity to pick a name for the element and they went with roentgenium, honouring Wilhelm Conrad Roentgen, who discovered X-rays in 1895.

Since 2004, when IUPAC officially accepted the name, element number 111 has been roentgenium, with a symbol Rg. In that same year, during the discovery of element 115, scientists identified as isotope of roentgenium in its decay chain, offering scope for studying it further.

With very few atoms of roentgenium ever produced and with its longest-lived isotope known currently having a half-life of a little over 20 seconds, a lot remains unknown yet regarding element 111.

 

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French chemist Antoine Lavoisier (1743-1794) is a celebrated scientist and nobleman who was central to the chemical revolution in the 18th Century. A meticulous experimenter who changed the way chemistry was done and perceived, he had a large influence on how both chemistry and biology developed. While it is impossible to cover everything that Lavoisier achieved in a short article, we will be looking at how one of his predictions came true nearly 100 years later.

A prophetic idea

Lavoisier had a prophetic idea that “[t]he air, or at least some of its constituents, would cease to remain an invisible gas and would turn into the liquid stage. A transformation of this kind would thus produce new liquids of which we as yet have no idea.” Given that until 1877, the dominant thought was that the permanent gases – oxygen, hydrogen, nitrogen and carbon monoxide – were not capable of existing in liquid form, such a statement was indeed beyond his time.

And yet, it did come true. For within days of each other, French physicist Louis Paul Cailletet and Swiss physicist Raoul Pictet arrived independently at methods for the liquefaction of oxygen in December 1877. A whole new field of research and science then opened up.

Born in 1832 into an industrial family, Cailletet was privileged to attend Lycee Henri IV in Paris, and the Ecole des Mines as an unregistered student. He returned to work on his father’s ironworks after his studies, and even though his exact nature of work remains unknown, it is evident that he applied the knowledge he had acquired while studying.

Observations in ironworks

Starting 1856, Cailletet published his studies based on observations in the ironworks and techniques to improve the quality of products. Most of these were presented by French chemist Henri Etienne Sainte-Claire Deville, a person with whom Cailletet shared a friendship that when beyond the typical Parisian scientific environment.

So when Deville became director of the chemistry laboratory at the Ecole Normale Superieure in 1868, it was no surprise that Cailletet also switched to a new series of experiments a year later – experiments that were no longer directly related to observations from ironworks. In 1869, Cailletet started experiments on high-pressure chemistry and most of his publications thereon dealt with compressibility of gases.

In 1877, Cailletet successfully attempted liquefaction of gases with an experimental arrangement based on a compression apparatus. Cailletet paced oxygen and carbon monoxide into his liquefaction apparatus on separate occasions, cooled and compressed them to a specific temperature and pressure and let the gases expand. He observed a thick mist at the end of the expansion and was able to identify that these were the condensed form of both gases.

 Deville is in the detail

Cailletet shot a letter to Deville on December 2, 1877, announcing the liquefaction of oxygen and carbon monoxide. Deville had the presence of mind to seal the letter in an envelope and deposit it with the Academie des Sciences. As a result, even when the Academie received a telegram from Pictet on December 22 stating that he had liquefied oxygen, there was no confusion over who got there first.

Pictet denied any priority claim and there was no dispute between the two parties. Pictet and Cailletet arrived at their results using different techniques and both of them were awarded the Davy Medal by the Royal Society of London in 1878.

Pictet proved to be an exception as a number of others jumped in and disputes ensued, Parallel priority claims were a constant theme between 1877 and 1908, during which time all the so-called permanent gases were liquefied. Cailletet’s liquefaction of oxygen had thus heralded cryogenics – a new field of research that concerned itself with the produced and behaviour of materials at very low temperatures.

 

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