Science Fair Rules

Editor,

Regarding the problem with science fair rules described in "Backscatter" for 24 February 2006, there may be one more factor in play here. While fear of lawsuits is a large issue, state science standards may apply. Many of them emphasize science ethics and even have special section on experiments on humans. If the local teachers and administrators take these guidelines for education too literally, they will be placing these restrictions on the students. Perhaps, they're just trying to show students what "real" science is like, by example.

I concur with Dr. Carlson's critique. However, much of teaching these day is "by the book" in the worst sense. Perhaps, the correspondent has encountered one of these situations.

Harry

Harry E. Keller, Ph.D.
President
ParaComp, Inc.
310-773-4293

A Simple Way to make Calcium Carbonate

Editor,

Could you tell me if there is anyway I can make sodium carbonate out of simple chemicals at home? I would appreciate hearing from you.

Thank you.

Jack Collins

Shawn Carlson suggested that we ask Norman Stanley to reply to your question, and Norm kindly sent the following reply. Editor.

Hello Jack:

Forrest has asked me to address your question about preparing sodium carbonate. It's very easy to do. All you need to do is heat sodium bicarbonate ("baking soda" available at your supermarket) to 100 C or higher. The higher the temperature the faster the reaction goes:

2NaHC₃ -----> Na₂CO₃ + H₂O + CO₂

The anhydrous carbonate is commonly known as "soda ash". Unlike the bicarbonate it is highly soluble in water. If the solution is concentrated by evaporation, the decahydrate, Na₂CO₃.10H₂O, will crystallize out. This form used to be available at grocery and hardware stores as "washing soda" but has been superceded by more efficient detergents.

Commercial production still relies on the venerable Solvay Process. In this process a saturated salt solution is saturated with ammonia and carbon dioxide:

NaCl + NH₃ + CO₂ + H₂O -----> NaHCO₃ + NH₄Cl

The sparingly soluble bicarbonate precipitates out and is filtered off and heated to produce the carbonate. The ammonium chloride byproduct is treated with calcium hydroxide to liberate ammonia which is then recycled into the process stream. Thus the raw materials consumed in the process are basically salt and limestone (source of CO₂ and Ca(OH)₂). Success of the process depends on the low solubility of the intermediate bicarbonate.

Norman Stanley

More About Celsius-Fahrenheit Conversions

Editor,

Regarding Tom Gartner's letter in "Backscatter" (The Citizen Scientist, 24 February 2006), I deduce the formulae remembering only that 9/5, 5/9 and 32 are involved in the conversions.

Consider the boiling point of water. Its Fahrenheit temperature is a larger number than the Celsius equivalent: converting from C to F one must multiply by 9/5 and from F to C, 5/9.

Now consider the freezing point of water. Converting either way, 0 has to be multiplied by the fraction. Thus, the 32 has to be subtracted from the Fahrenheit 32 before multiplying by 5/9, and the Celsius 0 has to be multiplied by 9/5 before adding the 32.

Ian Stirling

Most countries use the Celsius scale. The Fahrenheit scale has as an advantage nearly double the resolution between the freezing and boiling points of water. Editor.

To Dr. Larry Hill from James Farr: Thanks for the Idea.

Dear Dr. Hill,

Thanks for the idea ("Backscatter," The Citizen Scientist, 24 February 2006).

I'm going to ask the National Seashore here on Long island if they might be interested in starting a snapping turtle study using tagged turtles. They already have a tagging study that has been ongoing for the last thirty or forty years.It was started by Dr. John Nichols of the Museum of Natural History. When I was young, I sometimes assisted Dr. Nichols.

James Farr

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