Comment About An Acidic Question

Editor,

Regarding An Acidic Question for Shawn Carlson in Backscatter (2 March 2007), I suggest that Bob try his suggestion of substituting a soluble nitrate (e.g., KNO 3 or NaNO 3 ) for concentrated HNO 3 before getting into the hassle of trying to buy or make it. The reagent or commercial grade of nitric acid contains about 75% HNO 3 , so you will need the equivalent of 0.75 parts HNO 3 . This would be 1.35 parts NaNO 3 or 1.60 parts KNO 3 dissolved in 3 parts conc. HCl. Maybe 0.25 parts of water should be added to replace that otherwise present in the conc. HNO 3 . I doubt if these proportions are too critical. You can try the concoction on a test piece to see if it's a satisfactory etchant.

Red fuming nitric acid is a solution of dinitrogen tetroxide, N 2 O 4 , in nearly anhydrous HNO 3 (white fuming nitric acid). Making the latter by heating KNO 3 with conc. H 2 SO 4 in a glass retort was a standard lab exercise in high school chemistry way back when. My hazy recollection is that the product was colorless. We did other fun things, like making nitrous oxide by heating ammonium nitrate (NH 4 NO 3 ), collecting the gas and demonstrating how it vigorously supported combustion of a taper. Repeating the experiment with ammonium nitrite (NH 4 NO 2 ) yielded N 2 which extinguished the taper. I guess that for safety's sake such demonstrations are now passé, but much is lost toward kindling enthusiasm in the young mind for what should be a fascinating discipline.

Norman Stanley

Another Comment About An Acidic Question

Editor,

Regarding An Acidic Question for Shawn Carlson , I use concentrated mineral acids all of the time. The easiest and best priced source that I use is Elemental Scientific. You can find them on the web. They supply to small labs and amateurs. If you order several pints at a time (like I do), the shipping and special packaging isn't too expensive (compared to other suppliers).

Also, muriatic acid makes a constant concentration solution when boiled for a time (actually, just below boiling works fine too). Just don't do it in your basement because the HCl gases will make everything rust.

I have been making nitric acid with the sodium nitrate-sulfuric acid method for over 30 years. I use it whenever I want fuming nitric acid, which makes some organic reactions go better. The acid coming over becomes more dilute the longer you run the reaction. You can order a small all-glass retort from Elemental Scientific that is ideal for making nitric acid by the old reaction. Simply put the end of the retort into a large test-tube in a beaker of ice-water, and there won't be a lot of fumes. But do it in the garage with the doors open anyway. I hope this is helpful.

Tim Kraemer

Readers, use great caution when working with acids. Follow all relevant safety precautions and never work in close proximity to children. Editor.


Honeybees and Data Loggers

Editor,

I noticed the data logger piece on honeybee hive temperatures (Forrest M. Mims III, Using a Data Logger to Record the Temperature Inside a Beehive , 2 February 2007). We lived in Oregon for nearly 10 years, and the company that I was part owner of (a consulting engineering firm) included civil engineering and hydrological studies in our services. Our hydrologist/civil engineer was constantly confounded at the requirement that flood insurance, flood studies, establishing flood plains and related matters be based on flood maps that were decades out of date but were official government publications. He designed and developed a simple and inexpensive logging device that he placed in the main storm water feeders into our main local drainage (Bear Creek in the Rogue River valley of South Oregon) to demonstrate how poorly the official maps represented seasonal flows and hydrological events. There are sophisticated and expensive loggers out there but we wanted something that was affordable for municipalities, counties, and small water district operators to use. The data loggers were all from Onset and we worked with them to develop the very simple mechanism that translated the linear motion of a float inside a PVC tube into a variable electrical signal that the logger could track and trend.

Moments after any significant rainfall event, the loggers could track and trend the rate of runoff, rate of rise of the tributary, and other data that could be compiled to show how the area might actually flood and drain given the existing condition of foliage, silt, rock, or other changes or improvements/degradation of the creek or tributary in real time. I believe they also set up one or two with telemetry for remote real-time readout.

Coincidentally, the year after the logger was developed, we experienced rains and flooding of historic proportions (see, for example, http://www.sou.edu/biology/faculty/rchristi/Flood.html ) and the loggers were in place to collect data. In short, the data that was collected pretty much tossed the flood maps out the window.

Equipment like this is fabulous to have. Efficient, affordable, compact, and reliable. Amazing.

Oscar Zuniga


Comment About Mark Valentine's Letter on Geothermal Energy Research

Editor,

This is in response to Mark Valentine's fascinating proposal " Geothermal Energy Research " in Backscatter in the February 2007 installment of "The Citizen Scientist."

TPVs (ThermoPhotoVoltaics) have some promise, at least in specialized applications. However, I'm not sure using them with (current) fiber optics will be very promising. The major problem will almost certainly be that traditional glass based fiber optics do not conduct very well in the infrared region of the spectrum (How well do they conduct? That might be an interesting project for a reader!). While it is certainly possible to use a different material other than "ordinary" glass, this may prove to be a huge materials science problem. (Note that there are MANY different kinds of material that we call glass, most of which have differing optical properties.)

Additionally, since fiber optics function by constraining the optical energy within the fiber, and since infrared frequencies have a much longer wavelength than visible light, the fiber optics may need to be larger. Both of these problems may certainly be overcome, but they imply that it may not be as easy as picking up an off the shelf fiber and attaching it to an infrared sensitive photovoltaic cell.

Another area which has some potential for harvesting either geothermal or waste heat energy is a Seebeck cell. Fortunately, these cells are readily available, and are coming down in price quite dramatically due to their use as Peltier cells in high end computers for cooling hot processors. The Seebeck effect is the reverse of the Peltier effect. The Seebeck effect takes a temperature differential and produces electrical power, while the Peltier effect takes electrical power and produces a temperature differential.

The major problem is that the voltage produced across a Seebeck cell is relatively tiny, although it is possible to connect many dozens (or even hundreds) of them in series to produce a more reasonable voltage. There are already commercial products using Seebeck cells (e.g., the Ecofan for woodstoves), although I'm not currently aware of any thermo-solar uses. This may be an interesting area for research. I recently acquired some Seebeck cells via an on-line auction. They consist of approximately 256 junctions in series in a package that measures about 2.5 x 2.5 cm (1 x 1 inch).

David W. Glass

Frozen Cactus Needles

Editor,

Regarding the photo in Coping with Ice (Forrest M. Mims III, Gallery, 2 March 2007), do you have any ideas about why the ice on the cactus had such an unusual shape? Were the other needles coated with the same shape?

Could this shape be telling something about the way heat is transfer from or to a cactus needle?

For many years I have wondered if there is a heat transfer mechanism for cactus needles.

Chuck Ernst

Chuck, I photographed a dozen or so ice-coated cactus needles. Only one needle appeared to have a uniform coating of ice. All the others had blobs and constrictions, some much more than the one in the Galley photo. I have no explanation for this. Readers, any ideas? Editor .

Following the Flow

Editor,

Subtle airflow patterns in a house can be difficult to sense. Knowing them may reveal doors and windows that don't seal well and that could be sealed better to reduce energy use. Knowledge of airflow patterns may also help in deciding where to place a smoke detector.

Follow the standard guidelines and manufacturer's instructions for smoke detector placement regarding distance from a ceiling or wall. Knowing the airflow patterns may help to make a decision of which particular wall (or which area of ceiling) to use.

To study home airflow patterns, I used to weight a small helium balloon with paper clips and clay (in a room that was tightly closed) to achieve neutral buoyancy, so that the balloon hovered without rising or falling). I then released the balloon outside the room and followed it from a distance.
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Tie a short string, at most 2 or 3 inches long, to the balloon. The string needs to be short because the length of the string limits how close the balloon can get to the floor. Tie the string to a standard size paper clip. Add small pieces of soft clay to the paper clip, until the added weight just balances the lift of the balloon. The balloon will then hover.

There were some surprises. My favorite was releasing the balloon on the third floor a moment before somebody went out the front door, closing it behind them. The balloon descended the flights of stairs, crossed the living room to within two feet of the front door, stopped, then bobbed up and down. What that revealed was the airflow when the door was open and the eddy currents created when the door closed.

Paul Sagi

Question for Dr. Shawn on Crystals

Dear Dr. Shawn,

Help! My Son is doing his science project on crystals. We are growing them using the Smithsonian crystal growing kit. The instructions say the powder to grow them is called "chemical crystal" powder. My question is will these grow to become "mineral crystals"? In other words, is chemical and mineral the same thing? Thank You.

[Name withheld]

Shawn Carlson Replies

A mineral is an element or chemical compound that is normally crystalline and that has been formed as a result of eological processes. Some of these, like halite (salt) are chemicals and minerals that can be grown at home. Sugars, being created by plants, do not form crystals by geological processes and do not qualify. So, a chemical crystal, like those in the Smithsonian kit, could be a mineral or not, depending on whether they are also formed naturally somewhere in the earth.

I hope this helps. Yours for great science,

Dr. Shawn

Thinking About Near-Earth Asteroids

Editor,

I request help from physicists to support or reject my inquiry regarding feasibility of altering current trajectory of Apophis. We have a space station in orbit, which is visited by launched vehicles. Earlier, composite vehicles were accelerated from earth orbit to the moon. We also have guidance systems which enable correction of weapon trajectory to hit another missile.

In my biological ignorance it seems possible to me to assemble a composite unmanned vehicle that can accelerate in its trajectory toward Apophis. Acceleration can have useful effects on mass and energy. A glancing blow could deflect the asteroid. Even if this project appears unnecessary, later; the experiments and practice may prove useful with other future asteroids .

Glen Hemerick

Rethinking a Book

Editor,

I have recently purchased a book through Amazon.com entitled The Final Theory, Rethinking our Scientific Legacy . The book has no index, notes or bibliography, but is well written in clear prose. The writer, Mark McCutcheon, purports to have discovered a new theory of gravity, among other things, which he calls "Expansion Theory."

Customer reviews, mostly 5 star, are enthusiastic. At chapter 2, as far as I got, I had the eureka moment that this book was a 417 page joke. Further reading did nothing to dispel that notion. Has anyone out there read this book? If so what do you think? Or if you'd like to read it, and don't want to risk your money, I'll send you mine, just to get it off my book shelf.

Dolores Bentham

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