“Purity” means something special in aesthetic terms, with its allusion to the look and communicative power of pure form. But in science, “purity” sometimes has a very different meaning. Photo by Bill Westmoreland


brutjournal's science-and-art contributor David Bjerklie is a science writer and editor, and former science reporter for TIME magazine. He is based in New Jersey and Minnesota. Evoking a sense of purity in nature, we've illustrated this article with photos by Bill Westmoreland.

by David Bjerklie

On first examination, the notion of purity in the world of science seems entirely straightforward. When chemists or materials scientists refer to a pure sample of an element, whether it’s gold, carbon, sulfur, lead or uranium, they simply mean that the only substance present in such a sample is that single named element.

In this sense, purity is something absolute. It may be regarded as the chemical counterpart of the oath a witness takes in court when he or she pledges to tell “the truth, the whole truth, and nothing but the truth.” In the real world, however, chemists have had to devise scales, or grades, of purity in order to meet the practical demands of measurement in a range of scientific, pharmaceutical, and industrial contexts.

Degrees of purity apply to the smelting and smithing of gold, for example, processes in which karats serve as the unit by which purity is measured (24-karat gold is 99.99% pure, 18-karat gold is 75% pure, and 12-karat gold is 50% pure).

Science measures "purity," often with great precision.

It’s also possible to produce pure samples of a particular chemical compound. Distilled water is pure H2O. What we refer to as “dry ice” is pure carbon dioxide (CO2) in its frozen state. Pure preparations of methane (CH4), sulfuric acid (H2SO4), ammonia (NH3), baking soda (NaHCO3,) and ordinary table salt (NaCl) can also be made.

The list of possible pure compounds is essentially endless. But note that there is a big difference between a compound and a mixture. A compound is still a single entity created by chemical bonds; a mixture is not. You could put bananas, yogurt, spices, and honey into a blender, for example, and hold the button down for as long as you’d like, but no matter how uniform and silky the result, that liquid would be a mixture, not a compound; in that instance, the idea of “purity” would not apply. Similarly, when it comes to a familiar, smelly tool of farming, there is no such thing as “pure manure,” even though, in another realm, that might be just what many politicians seem to be so capable of serving up so much of the time.

Does purity exist in nature? Ask a scientist — and bring some fine-tuned measuring instruments along with you.

Science also offers us a notion of purity that can seem counterintuitive — and deliciously appealing to the aesthetic sensibility of the brutjournal community. That’s the idea of “pure” nothing.

A perfect vacuum, for example. Most of us learned that deep space is a perfect vacuum, a perfect void, a complete absence of anything. It turns out that the physics of pure vacuums is a bit more complicated, but practically speaking, a cubic foot of deep space is indeed pure emptiness, containing 99.999999999999% of nothing, give or take a few decimal points. 

Researchers create vacuums here on Earth for a variety of experimental as well as engineering and manufacturing purposes. The ideal of purity as complete absence also has applications beyond vacuums. So-called cleanrooms, for example, strive to eliminate all airborne particulate matter, including the smallest floating motes of dust, in order to avoid contamination in nanoscale processes, including the production of semiconductors.

Untouched nature, in all its glory, offers a vivid example of what many poets, artists, and lovers of the outdoors have regarded as "pure."

Most cleanrooms attempt to keep any contaminants from entering the workspace, but there are cleanrooms that are engineered to keep contaminants from escaping the workspace, such as those used in the study of deadly pathogens. Cleanrooms employ a battery of filters, fans and air handlers to maintain strong barriers between their enclosed spaces and the rest of the world. Sterilization is another process that strives for pure absence by killing any and all forms of biological agents, including microbes, spores, and the misfolded fragments of proteins called prions, which are the cause of mad cow disease. 

While it is certainly the case that purity, in all its degrees and forms, is essential in the realms of science, technology and medicine, it bears noting that achieving or producing these forms of purity require human intervention. Scientifically speaking, purity is almost always an engineered state; true purity is a rarity in nature. Life on Earth walks, swims, crawls, flies through — and, in fact, is dependent on — impurities at every turn. 

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