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Real Science

The Chemistry of dry cleaning

Michael Rosenthal

(12/2017) The scientific publications I read, magazines and newspapers, are currently dominated by issues that relate to climate change. These discussions focus upon the differences in opinion and approach between the federal government and the scientific community. No compromises or resolution of the differences of opinion seem to be in sight, so Iím taking the liberty of taking a month off in reporting on these energy issues.

All of us have experience with dry cleaning. Dry cleaning isnít really dry, it utilizes solvents that are not water to clean clothes, and is utilized for clothing that would not do well being immersed in water. The first thing is to sort the submitted items and pretreat any really tough stains. The clothes are then "washed" in a machine with an organic chemical solvent. The solvent used most is perchloroethene, referred to as "perc" by the dry-cleaning industry. Perc is an organic chemical with a C-C double bond and 4 chlorine atoms.

Those of you who studied organic chemistry in college may be thinking that dry cleaning plants may not be the healthiest place to work. Indeed chemicals of this sort are toxic, and long-term exposure is not a good idea. Perc is classified as a probable carcinogen, and exposure may damage the liver and kidneys. Some 6.8 million kilograms of perc were utilized by the dry cleaning industry in 2012. These concerns have led to the seeking of alternatives to perc by the dry-cleaning industry, including 1-bromopropane, propylene glycol ethers, silicones, and high-pressure carbon dioxide. You may have noticed that your clothes returning from the dry cleaners often have a distinctive chemical smell about them until they air out.

When I went to college, there were nowhere near the safety precautions taken in the laboratory that we now implement. Laboratories are now better ventilated. Fume hoods, which are self-ventilating enclosures, are used for many experiments that involve more dangerous chemicals. Students are expected to wear slacks and long-sleeve shirts, and to utilize lab coats and wear goggles to protect the eyes at all times. Lab accidents do occur, and serious consequences are known to result. As I was finishing graduate school at The University of Illinois, a professor of chemistry of some distinction was fatally injured due to an explosion in his research lab. My thanks go to Andy Brunning in Chemical and Engineering News for providing the background for this explanation.

On a cheerier note, we have just enjoyed the season of fall leaves, typical of climates such as ours that have distinctive summers and winters. Leaves start out green, because they utilize a process called photosynthesis via the chemical transformation of air and water into sugar with the assistance of chlorophyll, the chemical that makes leaves green. As winter comes closer, chlorophyll production decreases with the less sunlight available, and the other pigments in leaves become evident, giving us oranges and reds. The exact coloring of fall foliage is the result of a mix of these red, orange, and yellow pigments. Such exposure, soil moisture, and temperature contribute to this process, and hence the variety of colors we see. As fall moves along, sunlight and frost kill off pigments, leaving behind tannin, which is brown. The brown leaves undergo cell breakdown, making them fragile, and wind and cold eventually remove them from the trees. In the spring, the process begins anew.

Letís take a look now at an important development beyond the earthís surface.

For thirteen years, NASAís Cassini spacecraft provided us with wonderful discoveries. It was launched in 1997 to bring us information about Saturn and its moons. The last contact was September 15, 2017, as it plunged into Saturnís atmosphere and vaporized. The spacecraft spent 13 years orbiting Saturn, studying the planet and its system after entering orbit on July 1, 2004. On the way it flew by Venus twice, Earth, the asteroid Masursky, and in December of 2000, Jupiter. It revealed the methane lakes of Titan, the subterranean ocean beneath the Saturn moon Enceladusís icy crust, and a host of moonlets in Saturnís rings. The rings are now believed to have been formed 100 million years ago. Scientists feel that this project revolutionized human understanding of the Saturn system. The mission has especially revolutionized our understanding of gas giants and has examined the potential for life to exist in the solar system beyond earth.

The ozone hole is a region of exceptionally depleted ozone in the stratosphere over the Antarctic. Ozone protects the earth from the effects of ultraviolet rays, and thus depleting of the ozone layer has serious consequences for life on earth. The good news is that the hole in the protective ozone layer is its smallest size since 1988. The hole is 1.2 million square miles smaller than last year, and it is still shrinking. The weather has an impact on its growth or shrinkage, but the reduction of the emission of ozone-depleting chemicals, a conscious human effort, has been the major cause in its protection. It is 30 years since the establishment of The Montreal Protocol, an international agreement that led to major global efforts to phase out the use of ozone-depleting chemicals. The culprits are chemicals that had been used in refrigerators, air-conditioners, and aerosol cans Ė chlorofluorocarbons Ė and replacing them with safer chemicals.

One of the scientific topics that tends to overwhelm us is that the universe is so large and that we are such a small part of it. Last month it was reported by a researcher at The University of Hawaii Institute for Astronomy that a small bright object was observed streaking across the sky. Because of the unique path it followed, it was concluded to be a space rock from another solar system. According to NASA, the object was an asteroid about 400 meters across and moving at a clip of 27 miles per second. The object had approached from above from the direction of the constellation Lyra and had been cruising through interstellar space at a rate of nearly 16 miles per second. It is now zooming toward another part of the galaxy toward the constellation Pegasus. No interstellar asteroid had ever been seen before!

Astronomers arenít entirely sure what this object is. They first called it a comet, but since it had no corona, a cloud of gas and dust that surrounds a cometís core, they thus declared it to be an asteroid. The astronomers are confident that it comes from outside our solar system. Further studies of it are underway before it disappears to try to determine its exact size, shape, and spin rate, and to analyze the colors of light emitted and absorbed by the object to determine its composition. I will keep alert for more information on this remarkable phenomenon.

Michael is former chemistry professor at Mount. St. Marys

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