Those of us who live in the Northern hemisphere have probably forgotten the comet because it was only visible to the naked eye of those who lived south of the equator. We are referring to Comet C/2001 Q4 (NEAT) , a rather neat name for a comet. Discovered three years earlier, the comet made its closest approach to Earth in May of 2004 when it came within 0.32 AU from our planet. That’s almost 48 million miles, and although that’s 18 million miles closer than Venus ever comes to us, it’s not very close compared to other comets, as revealed by the following list. In 1999, the small comet, P/SOHO 5, came within only 1.8 million km of us, only 4.7 times as far as the moon!
The more interesting thing about Comet NEAT is that its trajectory is hyperbolic. A hyperbola gives one the false impression that its source must come from outside the solar system. But Comet NEAT comes from the Oort cloud, one of two distinct regions of the solar system that gives birth to comets. Although the spherically shaped Oort Cloud is the source of long-period comets ( more than 200 years), encompassing the solar system between distances of 1000 AU to 100,000 AU, it is not uncommon for a gravitational disturbance to change an Oort-comet’s orbit from an elliptical to a hyperbolic shape. Currently, Comet NEAT is on its way out of our solar system, having crossed the orbit of Neptune in 2014. A NASA JPL applet tracks its location.
Comets are believed to contain the most pristine material left over from the presolar nebula. They provide hints about how complex molecular species are formed. Thanks to interferometry from the old BIMA array of 9 radio telescopes, methanol (CH3OH), carbon monoxide (CO), carbon monosulfide (CS), and methyl cyanide(CH3CN) were identified in Comet NEAT. Other compounds include alcohol, cyanide, even amino acids. It has been speculated that comets have brought us water along with the organic soup required for the origin of life.
One can associate chlorine with cubism’s style of simultaneously representing a subject from many viewpoints on the same canvas. In a way, it takes a cubist’s perspective to paint a complete picture of chlorine. A part of cellular electrolytes in the form of chloride, it’s a life-essential element. As part of an acid it initiates the digestion of protein in many animals. By isolating it we have been able to make disinfectants, one which keeps water free of contaminants between a water treatment plant and the tap at home. But others have used the elemental form as a weapon of war. Cl2 is an also intermediate in the production of a wide variety of industrial compounds, many of which are indispensable, while many others have turned out to be known or probable carcinogens.
Let us begin with how mankind first stumbled upon the element.
Chlorine was first prepared in 1774 by Swedish chemist Carl Wilhelm Scheele. He had produced the yellow-green gas by adding fuming muriatic acid or spiritus salis (fuming hydrochloric acid) to a fine powder of pyrulosite (a mineral containing manganese dioxide Figure 1). But a pair of flawed hypotheses prevented Scheele and others from realizing that the gas was a new element. The first idea that stood in the way was the phlogiston hypothesis.
Chemists at the time believed that metals, acids and combustible substances contained phlogiston, which was released in fires and corrosion. It was impossible not to notice the new gas(chlorine)’s suffocating odour and painful action on the lungs. It resembled dephlogisticated air(oxygen) by supporting combustion. The phlogiston hypothesis had proposed that in a closed space, a fire died out before the fuel was consumed because the air would become saturated with phlogiston. Dephlogisticated air had a greater capacity for phlogiston, which was their explanation for why oxygen was better than air at sustaining flames. Using the internal logic of the hypothesis, Scheele concluded that the pyrulosite had taken away the phlogiston from the acid, and so he called the gas “dephlogisticated muriatic acid”.
A few years later, after Lavoisier had refuted the phlogiston hypothesis by revealing the role of oxygen in combustion, a second idea stood in the way of understanding the nature of chlorine. Lavoisier had incorrectly proposed that all acids contained oxygen. Chemists who had accepted his views thought of muriatic acid as an oxygen-bound compound. Davy realized that when muriatic acid and water were added to potassium, the potassium was liberating hydrogen from the acid and then from water. Any oxygen that went into solution (as hydroxide) was coming from water, not from the muriatic acid. Since experiments that had tried to separate chlorine gas into other substances had all failed, Davy concluded that muriatic acid was a compound of only hydrogen and chlorine and that chlorine was a new element.