Oenobareus

From the Greek meaning 'heavy with wine'
A blog devoted to science and reason
Written after a glass or two of Pinot Noir.
Showing posts with label electricity. Show all posts
Showing posts with label electricity. Show all posts

Saturday, February 9, 2013

An Inventory of the Furniture in Dr. Priestley's Study


Professor Eckstrom, a colleague of mine in the English department at Rio Hondo College, passed along a couple of poems.  They were written by Anna Laeticia Barbauld (née Aikin).  The first, reprinted below, is An Inventory of the Furniture in Dr. Priestley's Study; the second is The Mouse's Petition (To Dr. Priestly) that Prof. Eckstrom tells me is about a mouse that inhabited Priestley's study.

Portrait by Ellen Sharples, 1794,
National Portrait Galleery, London.
Joseph Priestly is usually credited with the discover of oxygen - what he called dephlogisticated air.  In his study of gases, he also discovered nitric oxide (nitrous air), hydrochloric acid (vapor of the spirit of salt), ammonia (alkaline air), and nitrous oxide (diminished air).  Priestley also wrote The History and Present State of Electricity, the authoritative text that was widely used for over hundred years.  In this text is the first demonstration of the inverse square nature of the electrostatic force and a detailed description of Benjamin Franklin's kite experiment.

In 1761, Priestley moved to Warrington, not far from Liverpool and Manchester.  He became a tutor at an academy where Barbauld's father also taught.  She became good friends with Priestley and his wife.  

Now to the poetry.



An Inventory of the Furniture in Dr. Priestley's Study

A map of every country known, 
With not a foot of land his own. 
A list of folks that kicked a dust 
On this poor globe, from Ptol. the First; 
He hopes,–indeed it is but fair,– 
Some day to get a corner there. 
A group of all the British kings, 
Fair emblem! on a packthread swings. 
The Fathers, ranged in goodly row, 
A decent, venerable show, 
Writ a great while ago, they tell us, 
And many an inch o'ertop their fellows. 
A Juvenal to hunt for mottos; 
And Ovid's tales of nymphs and grottos. 
The meek-robed lawyers, all in white; 
Pure as the lamb,–at least, to sight. 
A shelf of bottles, jar and phial, 
By which the rogues he can defy all,– 
All filled with lightning keen and genuine, 
And many a little imp he'll pen you in; 
Which, like Le Sage's sprite, let out, 
Among the neighbors makes a rout; 
Brings down the lightning on their houses, 
And kills their geese, and frights their spouses. 
A rare thermometer, by which 
He settles, to the nicest pitch, 
The just degrees of heat, to raise 
Sermons, or politics, or plays. 
Papers and books, a strange mixed olio, 
From shilling touch to pompous folio; 
Answer, remark, reply, rejoinder, 
Fresh from the mint, all stamped and coined here; 
Like new-made glass, set by to cool, 
Before it bears the workman's tool. 
A blotted proof-sheet, wet from Bowling. 
–"How can a man his anger hold in?"– 
Forgotten rimes, and college themes, 
Worm-eaten plans, and embryo schemes;– 
A mass of heterogenous matter, 
A chaos dark, nor land nor water;– 
New books, like new-born infants, stand, 
Waiting the printer's clothing hand;– 
Others, a motley ragged brood, 
Their limbs unfashioned all, and rude, 
Like Cadmus' half-formed men appear; 
One rears a helm, one lifts a spear, 
And feet were lopped and fingers torn 
Before their fellow limbs were born; 
A leg began to kick and sprawl 
Before the head was seen at all, 
Which quiet as a mushroom lay 
Till crumbling hillocks gave it way; 
And all, like controversial writing, 
Were born with teeth, and sprung up fighting.
"But what is this," I hear you cry, 
"Which saucily provokes my eye?"– 
A thing unknown, without a name, 
Born of the air, and doomed to flame.



Sunday, November 27, 2011

Don't Ask Marilyn a Physics Question


Marilyn needs a physics class. A chemistry class would help, too.  In this morning's Parade magazine*, Marilyn vow Savant answered the question "Is it true that if water is 100 percent pure, it will not conduct electricity?" with "Yes."

Uh, no.

Electricity is the motion of electrically charged particles.  Most commonly, it is the motion of electrons in metal wires that most people think of as electricity.  However, in batteries and other electrochemical applications, both positive and negative ions are moving.  How well a substance conducts electricity depends on a number of factors such as the number of charged particles, the distance the charges have to travel, the area through with they move, the temperature of the material, complex interactions with the atoms and molecules, and the applied voltage.

Tap water is a poor conductor; copper is about 10 billion times better**.  Adding ions makes it somewhat better.   Copper is only 10 million times better than sea water. In other words, sea water is around 1000 times better at conducting electricity than drinking water.

So it makes some sense to think that if one were to remove all impurities from water than it wouldn't conduct at all.  Except…

Water autodissociates.  Even in pure water, there are hydronium ions (H30+) and hydroxide ions (OH-).
Chemists have a way to express how much hydronium ions are in solution; it's called pH, the logarithm (base 10) of the H3O+ concentration.  Pure water at room temperature has a pH 0f 7.  

Therefore, pure water will conduct**.

There are other substances that one might think don't conduct electricity - air and glass, for example.  Under normal conditions they don't, but if I were to apply enough of a voltage, even these materials will conduct.  Remember this the next time you watch a lightning storm.

NOTES:
*As of noon on Nov. 27, neither Parade.com nor www.marilynvossavant.com have a link to this column.  When one appears, I will update the blog.  UPDATE: The link to the column is http://www.parade.com/askmarilyn/2011/11/Sundays-Column-11-27-11.html.

** Pure water has a conductivity of 5.5 X 10^-6 S/m.  For comparison, copper has a conductivity of 5.96 X 10^7 S/m.  

Friday, September 2, 2011

Maxwell's Silver Magnet (apologies to the Beatles)

In the post on wine swirling, i didn't bring up one of of Ralph de Amicis' incorrect comments, because there were so many that were wrong. This one though, deserves it's own post.

The positive pole is more highly charged, just like the North Pole of the Earth,…

A frequent mistake that people make is to mix up the electric charge with the magnetic pole. Both are basic characteristics of matter, just as mass is, but they're not interchangeable. Incredibly, I've even heard one of my science colleagues make this mistake in his class.

When I rub a balloon on my sweater, the balloon rips electrons from the fibers. When I put the balloon near the wall, those extra electrons on the balloon repel the electrons near the surface of the wall leaving a slight deficit of electrons (or a slight surplus of protons). Now notice those little plus (+) signs and negative (-) signs. Benjamin Franklin realized that electric charge comes in two types. He named them positive and negative. I think those are rather apt names, because in mathematics a negative sign can mean 'opposite.'

Now let's play with a magnet. When I place a magnet near a compass which is just a small magnet, I notice that the one end of the compass (white in the figure) is attracted to the red end of the magnet and vice-versa. I also notice that the red end of the compass is repelled by the red end of the magnet. When I take the compass outside, I see that the red end always points North. Historical note: The Chinese invented the compass 4500 years ago.

Since not all magnets have red and white ends, we need to name the two ends. I guess that since the red end points toward the North Pole, some ancient people (probably either the Chinese or the Greeks) called that end the north pole and the other end the south pole. Now look at the figure with the Earth. Since the north pole of the compass (the red end) points toward the North Pole of the Earth, the North Pole is really a magnetic south pole. Every semester when I teach this, I wish we used the terms red end and white end.

Two separate characteristics, two different phenomena. Charges created static electricity. Poles create magnetism.

What's really cool though is that although charge and pole are different characteristics of matter, they are related. Scientists like Faraday and Maxwell realized in the 19th century that by moving charges (like in electrical currents), we can create an electromagnet and by moving magnets we can create electrical current. These are the principles that give us electrical motors and generators.