"I think that I have one," Stacey speaks up. "Not exactly a breakthrough, but..."
"Wait," says Ralph.
Ralph interrupting. That's new.
In an apologetic tone he explains, "Before we go off on a different angle, I'd like to return to where we were yesterday. I think we were too hasty in our decision that classification of data can't lead to something good. May I?"
"Sure," Stacey says, almost in relief.
"Well," Ralph fidgets, apparently uncomfortable, "as you know, or maybe you don't, I minored in chemistry in college. I don't know much about it, but one story stuck in my mind. Last night I looked back at my notes from class and I think you'll find it interesting as well. It's a story about a remarkable Russian named Mendeleev, and it happened less than one hundred fifty years ago."
Noticing that he grabbed our attention, he becomes more confident. Ralph is a family man and has three little children, so he's probably used to telling stories.
"Right from the start, in the days of ancient Greece, people postulated that underlying the phenomenal variety of materials there must be a simple set of elements from which all other sub- stances are composed."
As he gets into his story his voice becomes rich with under- tones.
"The Greeks naively assumed that the elements were air, earth, water and..."
"Fire," Bob completes the list.
"Correct," says Ralph.
What a wasted talent. He's a real story teller, I think to my- self. Who would have suspected it?
"Since then, as you know, people have proven that earth is
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not a basic element but actually composed of many different more basic minerals. Air is composed of different types of gases, and even water is a composition of more basic elements, hydro- gen and oxygen. The kiss of death to the naive Greece approach came at the end of the eighteenth century, when Lavoisier showed that fire is not a substance but rather a process, the pro- cess of attachment to oxygen."
"Over many years, out of the chemists' mammoth work, the more basic elements emerged and by the middle of the nine- teenth century, sixty-three elements had been identified. The sit- uation actually resembled our colored board. Many circles, rec- tangles, stars, and other shapes, in many colors and sizes filled the area with no apparent order. A real mess."
"Many tried to organize the elements but no one succeeded in offering anything that was not immediately dismissed as a fu- tile arbitrary exercise. It got to the point that most chemists gave up on the possibility of finding any generic order and concen- trated their efforts on finding more hard facts regarding the com- bination of the elements to create other, more complicated mate- rials."
"Makes sense," Bob remarks. "I like practical people."
"Yes Bob," Ralph smiles at him, "But there was one profes- sor who claimed that in his eyes it resembled dealing with the leaves while nobody had found yet the trunk."
"Good point," says Lou.
"So this peculiar Russian professor who, by the way, taught in Paris, decided to concentrate on revealing the underlying or- der governing the elements. How would you go about it?"
"Shape is out of the question," Stacey says, looking at Bob.
"Why? What do you have against shapes?" Bob demands.
"Out of the question," she repeats. "Some of the elements are gases, some are liquids."
"Yeah, you're right." Being Bob he continues, "But what about color? You like colors, don't you? Some gases have colors, like green chlorine, and we can say that the others have transpar- ent colors."
"Nice try," Ralph says, ignoring their apparent attempt to ridicule his story. "Unfortunately some elements do not have a decisive color. Take pure carbon, for example. It appears as black graphite, or more rarely as a sparkling diamond."
"I prefer diamonds," Stacey jokes.
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We all laugh, then responding to Ralph's gesture I give it a try. "We probably have to look for a more numerical measure. This way we'll be able to arrange the elements without being criticized for subjective preferences."
"Very good," says Ralph. He's probably mistaken us for his kids. "What do you suggest as a suitable measure?" he asks me.
"I didn't take chemistry," I reply, "not even as a minor. How would I know?" But since I don't want to offend Ralph I con- tinue, "Maybe something like specific gravity, electrical conduc- tivity, or something more fancy like the number of calories ab- sorbed or released when the element is combining with a reference element like oxygen."
"Not bad, not bad at all. Mendeleev took basically the same approach. He chose to use a quantitative measurement that was known for each element and which didn't change as a function of the temperature or the state of the substance. It was the quantity known as atomic weight, which represents the ratio between the weight of one atom of the given element and the weight of one atom of the lightest element, hydrogen. This number provided Mendeleev with a unique numerical identifier for each element."
"Big deal," Bob can't hold himself. "Exactly as I suspected, now he could organize all the elements according to their ascend- ing atomic weights, like soldiers in a line. But what good does it do? What practical things can possibly come out of it? Like I said, children playing with lead soldiers, pretending that they do very important work."
"Not so fast," Ralph responds. "If Mendeleev had stopped here, I would accept your criticism, but he took it a step further. He didn't arrange the elements in a line. He had noticed that each seventh soldier represents basically the same chemical be- havior, though with increased intensity. Thus he organized the elements in a table with seven columns.
"In this way all the elements were displayed according to ascending atomic weight, and in each column you find elements with the same chemical behavior in ascending intensity. For ex- ample, in the first column of his table stood lithium, which is the lightest of all metals, and which, when put into water, becomes warm. Right below it is sodium, which when put into water, flames. Then the next one in the same column is potassium, which reacts even more violently to water. The last one is cesium which flames even in regular air."
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"Very nice, but as I suspected it's nothing more than child's play. What are the practical implications?" Down-to-earth Bob.
"There were practical ramifications," Ralph answers. "You see, when Mendeleev constructed his table, not all the elements were already found. This caused some holes in his table that he reacted to by 'inventing' the appropriate missing elements. His classification gave him the ability to predict their weight and other properties. You must agree that's a real achievement."
"How was it accepted by the other scientists of his time?" I ask, curious. "Inventing new elements must have been received with some skepticism."
"Skepticism is an understatement. Mendeleev became the laughing stock of the entire community. Especially when his table was not as neatly arranged as I described it to you. Hydrogen was floating there above the table, not actually in any column, and some rows didn't have one element in their seventh column, but a hodgepodge of several elements crowded into one spot."
"So what happened at the end?" Stacey impatiently asks. "Did his predictions come true?"
"Yes," says Ralph, "and with surprising accuracy. It took some years, but while he was still alive all the elements that Mendeleev predicted were found. The last of the elements that he 'invented' was found sixteen years later. He had predicted it would be a dark gray metal. It was. He predicted that its atomic weight would be about 72; in reality it was 72.32. Its specific gravity he thought would be about 5.5, and it was 5.47."
"I bet nobody laughed at him then."
"Certainly not. The attitude switched to admiration and his periodic table is regarded by students of chemistry today as basic as the ten commandments."