Chemistry: This Day in Science History - July 28 - Charles Townes

Chemistry Get the latest headlines from the Chemistry GuideSite.

This Day in Science History - July 28 - Charles Townes Jul 27th 2011, 22:05 July 28th is Charles Townes birthday. Townes was the American physicist who created the first working maser. A maser is a device that was the precursor to the laser that amplifies microwave radiation instead of light. Townes worked on a system that used ammonia molecules in a cylindrical cage with metal rods. The rods would be alternately charged to produce an electric field that would excite the electrons in the ammonia and separate excited ions from unexcited ions. The excited ions left the end of the resonator through a small hole. The resulting radiation was of very low power, on the order of a microwatt, but the wavelength was constant. Masers operate using a different method now, but the principle is the same. They are used to amplify microwaves, radar, and even in radio astronomy to detect very weak signals over a great distance. Find out what else occurred on this day in science history. Follow Chemistry on Facebook or Twitter.

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Chemistry: 6th Grade Science Quiz

Chemistry Get the latest headlines from the Chemistry GuideSite.

6th Grade Science Quiz Jul 27th 2011, 10:11 Sounds easy, right? It turns out you probably knew most of the science you ever learned by the time you were in 6th grade. Do you remember it or did you learn it in the first place? Take the new quiz and find out.

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Chemistry: What's Hot Now: What Causes Rigor Mortis?

Chemistry: What's Hot Now These articles that had the largest increase in popularity over the last week

What Causes Rigor Mortis? Jul 27th 2011, 10:03 A few hours after a person or animal dies, the joints of the body stiffen and become locked in place. This stiffening is called rigor mortis. Depending on temperature and other conditions, rigor mortis lasts approximately 72 hours. The phenomenon is caused by the skeletal muscles partially contracting. The muscles are unable to relax, so the joints become fixed in place. More specifically, what happens is that the membranes of muscle cells become more permeable to calcium ions. Living muscle cells expend energy to transport calcium ions to the outside of the cells. The calcium ions that flow into the muscle cells promote the cross-bridge attachment between actin and myosin, two types of fibers that work together in muscle contraction. The muscle fibers ratchet shorter and shorter until they are fully contracted or as long as the neurotransmitter acetylcholine and the energy molecule adenosine triphosphate (ATP) are present. However, muscles need ATP in order to release from a contracted state (it is used to pump the calcium out of the cells so the fibers can unlatch from each other). ATP reserves are quickly exhausted from the muscle contraction and other cellular processes. This means that the actin and myosin fibers will remain linked until the muscles themselves start to decompose. Rigor mortis can be used to help estimate time of death. The onset of rigor mortis may range from 10 minutes to several hours, depending on factors including temperature (rapid cooling of a body can inhibit rigor mortis, but it occurs upon thawing). Maximum stiffness is reached around 12-24 hours post mortem. Facial muscles are affected first, with the rigor then spreading to other parts of the body. The joints are stiff for 1-3 days, but after this time general tissue decay and leaking of lysosomal intracellular digestive enzymes will cause the muscles to relax. It is interesting to note that meat is generally considered to be more tender if it is eaten after rigor mortis has passed. Recent Chemistry Articles

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Chemistry: What's Hot Now: Unit Conversions Test Questions

Chemistry: What's Hot Now These articles that had the largest increase in popularity over the last week

Unit Conversions Test Questions Jul 27th 2011, 10:03 This is a collection of ten chemistry test questions with answers dealing with unit conversions. Question 1 Convert the following measurements into m. a. 280 cm b. 56100 mm c. 3.7 km Question 2 Convert the following measurements into mL. a. 0.75 liters b. 3.2 x 104 μL c. 0.5 m3 Question 3 Which is greater: 45 kg or 4500 g? Question 4 Which is greater? 45 miles or 63 km? Question 5 How many cubic feet are there in a room measuring 5m x 10m x 2m? Question 6 What is the volume of a 12-oz can of soda in mL? Question 7 What is the mass of a 120 lb person in grams? Question 8 What is the height in meters of a 5'3" person? Question 9 6 gallons of gasoline costs $21.00. How does a liter cost? Question 10 A man makes a 27.0 km trip in 16 minutes. a. How far was the trip in miles? b. If the speed limit was 55 miles per hour, was the driver speeding? Answers 1. a. 2.8 m   b. 56.1 m   c. 3700 m 2. a. 750 mL   b. 32 mL   c. 5 x 105 mL 3. 45 kg 4. 45 miles (72.4 km) 5. 3531.47 ft3 6. 354.9 mL 7. 54431 grams 8. 1.60 m 9. $0.92 10. a. 16.8 miles   b. Yes (63 mph)

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Chemistry: This Day in Science History - July 27 - John Dalton

Chemistry Get the latest headlines from the Chemistry GuideSite.

This Day in Science History - July 27 - John Dalton Jul 26th 2011, 22:05 On July 27, 1844 John Dalton died. Dalton was an English chemist and physicist who proposed what has become known as Dalton's atomic theory. This theory puts forth the idea that elements are made up of very small units, or atoms. These atoms are the smallest unit of mass that cannot be destroyed by chemical means. All atoms of a particular element are identical to each other. Dalton's theory also says chemical compounds are formed by combining two or more different kinds of atoms and that a chemical reaction is just the rearrangement of atoms. This theory explained many unknown chemical phenomenon of the time and was quickly adopted by chemists. Today, we see flaws with the overall theory. Dalton had no idea of the existence of parts of atoms and the existence of isotopes. He also didn't know that atoms could be created or destroyed through nuclear processes. In spite of this, his basic theory lives on in modern chemistry. Find out what else occurred on this day in science history. Follow Chemistry on Facebook or Twitter.

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Chemistry: Want to Repel Bugs? Smell Like Death!

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Want to Repel Bugs? Smell Like Death! Jul 26th 2011, 12:04 Have you ever noticed how bugs avoid the bug zapper, even though it may be crammed-to-bursting with tasty bug-barbeque? The same holds true for any dead bug you may have in your house. The cat might bat at it, but other bugs will leave the deceased in peace. Why is this? It turns out the smell of (bug) death repels others bugs. Researchers have discovered you can keep cockroaches (insects, yes I know the difference, but let's just call them bugs here) at bay by smearing dead cockroach guts as a repellent. The active ingredient consists of fatty acids formed during the decay process. These fatty acids also repel ants and caterpillars as well as buggy crustaceans like woodlice and pillbugs. While the chemicals are smelly to cockroaches and other arthropods, the levels that repel bugs aren't offensive to humans. This particular natural bug repellent may sound pretty nasty, but if you find a dead cockroach (for example) in your house, you can help keep its friends away by scattering the remains. Of course, it's likely the reason dead bugs repel other bugs is because death can signal the presence of poison or disease, so this isn't something I'd recommend testing in your kitchen.

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Chemistry: What's Hot Now: Atomic Structure and Periodic Table Quiz - Multiple Choice Test on Atomic Structure and the Periodic Table

Chemistry: What's Hot Now These articles that had the largest increase in popularity over the last week

Atomic Structure and Periodic Table Quiz - Multiple Choice Test on Atomic Structure and the Periodic Table Jul 26th 2011, 10:02 from Anne Helmenstine, Ph.D., Guide to ChemistryTest your understanding of atomic structure and the periodic table with this 10-question multiple choice quiz. Use the atomic structure and periodic table quiz to help yourself study for the AP chemistry exam or first year college chemistry test. You are welcome to refer to the periodic table while taking the quiz. Start the quiz again. AP Chemistry Course & Exam Topics Review Atoms & Ions Review the Periodic Table Atom Basics Quiz Atomic Structure Quiz

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