735 Riddle Road Cincinnati, Ohio 45220
I'm a molecule of water. Dinosaurs drank me. Throughout millennia, I have flowed in rivers and drifted in clouds. I have meant good health to countless plants and animals, including human beings. Life on earth could not exist without me. My experiences are innumerable, but, recently, in a place called Darke County, Ohio, I had quite an adventure, which I should like to recount.
First, permit me to describe myself. Despite the simplicity of my form, I am complex. Only two atoms of hydrogen and one atom of oxygen make up all of me. Without meaning to sound boastful, I would say my personality is magnetic even electrifying! My oxygen atom's center, called the nucleus, carries eight positive electrical charges. Eight negatively-charged electrons rapidly orbit the center. They form four parts. Every pair sticks together because the two electrons are spinning in opposite directions on their own axis, generating a magnetic attraction. The four pairs repel one another and keep far apart.
My two hydrogen atoms are much smaller than my oxygen atom like two grapes next to a grapefruit (only on an atomically-tiny scale). The center of each hydrogen atom (called a proton) bears a positive charge. Opposites attract. Thus, two of the four negatively-charged electron pairs grab fast to the two positively-charged hydrogen centers. The angle between my hydrogen atoms is just about 104 degrees.
The hydrogen proton is tiny; it can come close enough to the ample numbers of electron pairs of other water molecules to create additional bonds. (For that matter, each of the two hydrogen atoms contributes an electron of its own.) You see, because my hydrogen atoms connect to my oxygen atom at an angle less than 180°, one side of me is slightly more positive, the other side is a tad more negative. My positive side attracts the negative parts of other water molecules. So two or three or more water molecules can string themselves together. Even as weak as these hydrogen bonds indeed are, they make water a liquid, instead of a vapor (or gas), at ordinary temperatures on earth.
In a barrel of water, the hydrogen bonds keep forming and breaking down so that not all of the molecules are attached to other water molecules at any one time. Generally speaking, the hotter it gets, the faster I and my fellow molecules move and the hydrogen bonds linking us molecules can break. Then I fly off by myself as vapor. I don't need a high temperature to do this, but higher heat speeds up the process.
You probably have strolled out on the surface of a frozen lake in winter. Beneath the solid ice is liquid water, and above the ice if vapor. As you can recognize, water can exist in all three states at once: solid, liquid, and gas. For comparison's sake, iron is solid until heated to 2,795°. It then becomes a liquid up to 5,432°, when it finally transforms into a gas.
Petroleum is the only other naturally-occurring liquid compound existing in millions of tons on earth. But there is a billion billion times more water than petroleum! Even you are seventy percent water!
Now, on to my great adventure!
In July, I was happily minding my own business in a friendly string of water molecules in a well in Darke County, Ohio, when I found that I and about four hundred gallons of water had been pumped into a tank on wheels. This water wagon transported me and my companions across a grassy field. Then about half of the water, including me, was pumped from the first tank into a second one. When my friends and I happened to pass near the metal walls of our new enclosure, I felt warmer than when I had been lying in the cool well (where the temperature varied only about ten degrees year round and only one degree per day). The hydrogen bonds in my string held firm, nonetheless.
Without warning, I surged forward (pumped again! this time by a geared pump). I rushed along a feed-water pipe and into a closed, steel-shell heating mechanism. Here, I passed alongside tubes which radiated so much heat that my temperature skyrocketed from about 65° to 150°. (Before long, I would be passing through the inside of these same tubes but not until many amazing changes had occurred.)
It all happened so fast that it's only now that I have had time to sort it all out. Just when I thought I'd reach 200°, I was forced inside a boiler. The fiery heat thrilled me with a vague sensation of explosive possibilities. As you know, heat is both a quality to be felt and a quantity of energy which can do work. Water 1,350 pounds of it was boiling in this flange-steel cylindrical container measuring twenty-eight inches in diameter, about seven feet in length, and 9/32 of an inch in thickness. The potential for dynamic energy could be described only as tremendous. Thirty-six seamless-steel tubes, each two inches in diameter and 84 inches long, were conducting 400° combustion gases from a coal fire in a firebox in back of the boiler barrel to a smoke box and smokestack (or chimney) in front. These gases were chuffing through the tubes in a pulsating draft of up to eight chuffs per second. Those tubes exuded terrific heat, and, as we strings of water molecules churned around them in quick currents, we grew hotter and hotter and hotter!
The weak hydrogen bonds attaching me to my companions broke sooner than I had expected. I was suddenly free in the state of vapor, also known as steam. (Not all of my friends in the half-ton and more of water changed from liquid to gas so rapidly.)
Allow me to pause here long enough to explain a matter of great importance in light of what will follow. Out in the open air at approximately the level of the sea, a pint of water will evaporate into nearly twenty-seven cubic feet of steam. To put this same fact another way, I tell you that the steam from a pound of water at atmospheric pressure expands 1,600 times its volume in the liquid state. To transform liquid water to vapor requires enormous energy despite the relative weakness of the hydrogen bonds linking water molecules. Of all natural substances, water demands the most energy to accomplish this transmutation from liquid to gas. The same amount of energy to convert one pound of water to steam could melt three pounds of steel or thirteen pounds of gold.
Back to my astonishing tale ... When I abandoned the liquid state to become a molecule of steam in that boiler, I did so because I could draw on plenty of energy from the heat, which can help to do the work of changing from liquid to steam by breaking hydrogen bonds. But heat isn't the only story here; there was pressure, too. Once I was free, I wanted to fly far away from my fellow steam molecules, just as I would have done, had I been outside in the open air. But I couldn't!
I bubbled to the rolling surface of the water and leapt into the torrid space above, but the boiler shell imprisoned me. My temperature was precisely 327.75°, signifying that the pressure which I and my steamy colleagues were exerting against every square inch of the inner surface of that boiler was exactly 85.3 pounds. No wonder I hadn't boiled at the usual 212° but at a higher temperature the pressure inside was nearly six times greater than that of the atmosphere outside (14.7 pounds per square inch at sea level)!
I was invisible, dry, and rich with potential energy. I danced madly into a dome, then through a pipe which led me up, over, and down into a steam chest, where a sliding valve mechanism uncovered an exit for me and my comrades. This channel (or port) took me inside a cylinder nine inches in diameter and, as I would instantly discover, ten inches in length.
The pressure felt intense, but something gave way. My friends and I had pushed against a piston, which began to slide down the length of the cylinder. Shortly after I and my peers had been admitted to the cylinder, the port shut, cutting off the entry of any additional molecules. Still, a fourth of a trillion-trillion of us had made it in. If you were to count each one of us at the rate of one per second, it would take you 500,000 times the age of the universe to finish counting. We kept shoving that piston, relieving the pressure little by little. A few of my comrades huddled more closely together, reforming their hydrogen bonds and reverting to liquid. They had quit their rapid motion and their frenzy to expand. Why? Because they had yielded their energy to the rest of us to help us to expand farther (by pushing the piston). It's a little known fact, but expanding steam requires a small input of energy to expand. Consequently, a nearly-negligible amount of liquid water will form.
Many, many more of my peers also returned to the liquid state but for entirely different reasons. They became lethargic and reconstituted their hydrogen bonds that is, they condensed because they had approached the walls of the cylinder, which were a trifle less hot than the temperature of the steam.
Evidently, moments before my entrance into this space, steam had been exhausted from the cylinder through those tubes alongside of which I had passed in the heater. This action of exhausting had permitted the departing steam to carry off heat absorbed from the inner surface of the cylinder, left wet with a clammy film of liquid molecules sunk into lassitude. Those of the fresh steam molecules who had come in with me and were nearest to this surface imparted their energy to reheat the walls almost to the 327.75° of the boiler steam. I felt that this loss was a shame. After all, the energy given up to reheat the cylinder's innermost metallic skin could have been put to better use pushing the piston. What a purposeless decrease in the efficiency of the machine I was in!
Anyway, an immense number of steam molecules reverted to the liquid state, swirling as more and more mist while the piston traveled farther and farther toward the end of the ten-inch-long cylinder. The sliding of the piston had presented us energetic steam molecules a portion of the room we had wanted for expanding outward, but the work we had done in shoving that piston had depleted much of our energy. Soon, many of us were pooped.
At that moment, the port where I had entered the cylinder opened again, and I and my colleagues scrambled for it. Our combined pressure seriously declined, and a great deal of re-evaporation occurred. In other words, at the lowered pressure, the temperature was plenty to cause liquid molecules to jump back into a frantic boil as steam. I both pitied and deplored these molecules, most of them the same ones who initially had yielded their energy to reheat the metal of the cylinder's surface, for they had not done an honest day's work in pushing the piston. They had gone from steam, to liquid, and back to steam with the waste of misdirected effort.
I had virtually no time to consider them, however, while I dashed through the port and found that the passage led me in a new direction. Later, I learned that more fresh, or 'live', steam had entered the cylinder on the opposite side of the piston, thus compelling it to undergo a return trip. Not all my comrades escaped before the port closed again, and I am told that the returning piston compressed them. I am sure they valiantly pressed back against the piston and formed a cushion between it and the end of the cylinder a noble deed. Those of us who had been exhausted through the port carried off with us much precious heat energy from the inner walls of the cylinder. I remained sweltering, but before long I knew that I was inside the tubes of the heater and that energy was being drained from many of my friends. I suddenly understood that, from within those heater tubes, they were warming the feed water on the exterior of the metal in the same way that I had been heated at the outset of my wonderful journey toward and through the cylinder. I chuffed my way out of the heater, through an exhaust nozzle which launched me dizzily upward, and out the smokestack.
The blast of us molecules as we were jettisoned from the nozzle served to swell the draft up the smokestack, thereby assisting the hot combustion gases from the firebox to flash from the back of the boiler, through the fire-tubes, to the smoke box, and up the chimney. In contact with the cooler air, I calmed down enough to form hydrogen bonds with several of my comrades. I was liquid again water spiraling high above the smokestack where the force of the exhaust steam and the smoky draft propelled me.
Below stood a nine-ton, 50-horse-power Case traction engine. In my own small way, I had helped to run that powerful machine. During my odyssey, I had pressed that piston forward, its motion relayed as mechanical energy to the spinning crankshaft and revolving flywheel. I noticed a crowd of onlookers appreciating the spectacle of steam-powered machinery from the storied agricultural past of America. I felt proud. I had contributed in yet another way to the positive quality of life on earth.
Released from the convection currents, my molecular friends and I formed a droplet and fell, splashing on the nose of one of the spectators Bob Rhode, I think his name was.
For factual information, this article relies upon many sources, notable among them:
Boss, William. The Heath Book for Threshermen. Winnipeg: Heath, 1908.
Case catalogues, parts lists, and manuals (all reprints).
Deming, H. G. Water: The Fountain of Opportunity. New York: Oxford UP, 1975.
The Power Catechism. New York: McGraw, 1897.
Thurston, Robert H. History, Structure, and Theory of the Steam-Engine. New York: Wiley, 1904. Vol. 1 of A Manual of the Steam-Engine. 2 vols.
I am indebted to Dr. Charles E. Hawkins, professor of physics and director of academic computing at Northern Kentucky University, for valuable computations included in this essay.