The purpose of a test tube is to safely hold, mix, heat, or observe small quantities of liquids or solids during scientific work. Made most commonly from borosilicate glass, test tubes are used across chemistry for reactions and heating, in microbiology for growing cultures and detecting gas production, and in medicine for collecting and storing blood or fluid samples. Their simple, open-topped cylindrical shape makes them easy to fill, seal, label, and place safely in a rack between uses.
Where the Test Tube Actually Came From
Unlike some lab equipment with a single, well-documented inventor, the test tube's origin is genuinely a bit murky—and that's worth admitting rather than making up a tidy story.
The two most likely originators are Swedish chemist Jöns Jacob Berzelius and English scientist Michael Faraday, both of whom sketched tube-like vessels in their notes. Berzelius's earliest known sketch dates to around 1820, while Faraday's references come from the 1850s. Neither claim is fully settled, and historians still aren't certain which of the two deserves the credit—or whether one simply built on the other's idea.
What is clear is the moment that turned the test tube into the reliable workhorse we know today. In 1893, German chemist Otto Schott—founder of the glass company that still bears his name—developed borosilicate glass, branding it "Duran." A related, now more famous version, Pyrex, followed in 1908 when American scientist Eugene Sullivan developed it in the United States after encountering borosilicate glass while studying in Germany. That heat-resistant glass is the real reason this tube's usefulness expanded so dramatically—suddenly, the same tube that held a cold liquid could go straight over an open flame without shattering.
Why the Design Works So Well
Every part of a test tube's shape earns its place, and none of it is accidental.
The tube is typically 10 to 20 millimeters wide and 50 to 200 millimeters long, small enough to handle comfortably in one hand, yet large enough to hold a meaningful sample. The open top often flares slightly outward, which makes pouring liquid out—or in—noticeably easier. The bottom comes in a few shapes: flat, round, or conical, depending on whether the tube needs to stand upright on its own or sit in a rack or centrifuge.
Many test tubes also carry a small frosted or ground-glass patch near the top, just wide enough to jot a quick label in pencil—a small, low-tech detail that's genuinely saved countless experiments from turning into an unlabeled guessing game.
What Material Actually Matters Here
What a test tube is actually used for depends heavily on what it's made from, and the two most common materials serve very different jobs.
Borosilicate glass resists sudden temperature changes and most chemical attacks from acids, bases, and organic solvents, which is exactly why it's the standard choice for chemistry labs, heat sterilization, and any procedure involving a Bunsen burner or heating block.
Soda-lime glass is a cheaper, more basic alternative, but it can't handle rapid heating and cooling the way borosilicate can—fine for simple, room-temperature tasks, risky for anything involving a flame.
Plastic test tubes, introduced around the mid-20th century, added a disposable, shatter-resistant option that's now common in medical and biological settings where contamination control matters more than reusability.
The Real Purpose of a Test Tube in Chemistry
In a chemistry lab, this tool is refreshingly hands-on: mixing small quantities of reagents, running simple reactions, and observing color changes or precipitate formation up close. Because borosilicate versions handle direct heating well, they're also routinely used to warm a substance over a flame or in a heating block—something a plastic beaker could never survive.
Their resistance to chemical attack means they can hold acids, bases, and organic solvents without much concern, which is exactly why they show up constantly in titration prep, qualitative analysis, and general reagent testing.
The Purpose of a Test Tube in Microbiology
Step into a microbiology lab, and the job shifts from chemical reactions to living cultures. Test tubes filled with nutrient broth or agar provide a controlled, contamination-resistant space for bacteria, yeast, or fungi to grow.
One especially clever variation is the Durham tube—a tiny inverted test tube placed inside a larger one, first described in 1898 by British microbiologist Herbert Durham. As the larger tube's culture broth is sterilized (commonly at 121°C for 15 minutes), the trapped air inside the smaller tube escapes. If the microorganism being tested produces gas during fermentation, that gas collects visibly inside the small inverted tube—a simple, elegant way to confirm a specific metabolic activity without any complex instrumentation.
The Purpose of a Test Tube in Medicine
Walk into a hospital or diagnostic lab, and test tubes take on yet another job: collecting and storing blood and other bodily fluid samples for testing. Specialized blood collection tubes — often color-coded by cap to indicate which additive is inside — are a direct medical evolution of the same basic cylindrical design, adapted specifically for safe, standardized sample handling in clinical chemistry and immunoassay testing.
This medical application shows just how far this simple 19th-century chemistry-bench tool has stretched, without ever really changing its core shape.
Common Test Tube Variations and How They Differ
Not every tube that looks like a test tube serves the exact same purpose. A few worth knowing:
- Culture tubes are simple test tubes used specifically to grow microbial cultures, often capped with cotton, foam, or a screw lid to allow controlled air exchange.
- Centrifuge tubes are typically conical-bottomed and built to withstand high-speed spinning, separating components by density—a job standard test tubes aren't designed for.
- Durham tubes, as covered above, are miniature tubes used specifically for detecting gas production during fermentation testing.
- Blood collection tubes are specialized, often vacuum-sealed variants built for safe, standardized clinical sample collection.
Storing and Handling Test Tubes Properly
A test tube on its own doesn't stand up, which is exactly why test tube racks exist—keeping multiple tubes upright, organized, and safely separated during an experiment. Proper handling also matters: a hairline crack that looks harmless at room temperature can shatter the moment it meets a Bunsen burner flame, so a quick visual check before use is always worth the ten seconds it takes. Simple habits like this—checking for cracks, labeling clearly, and racking tubes properly between steps—are what actually keep a busy lab bench running smoothly, no matter how advanced the equipment around it gets.
Conclusion
The purpose of a test tube has never really been complicated—hold something small safely so it can be mixed, heated, grown, or examined without a mess. What's genuinely impressive is how far that simple job description has traveled: from Berzelius or Faraday's early 19th-century sketches, through Otto Schott's borosilicate breakthrough in 1893, all the way to Herbert Durham's gas-detection trick in 1898 and the specialized blood collection tubes used in hospitals today. Few pieces of lab equipment can claim to be equally at home in a school chemistry class, a microbiology culture room, and a hospital diagnostic lab—but the test tube manages all three without missing a beat.
Frequently Asked Questions
What is the main purpose of a test tube?
The main purpose of a test tube is to safely hold, mix, heat, or observe small quantities of liquid or solid substances during scientific experiments.
What is a test tube made of?
Most test tubes are made from borosilicate glass for heat and chemical resistance, though soda-lime glass and plastic versions are also common for less demanding or disposable applications.
Who invented the test tube?
The true inventor isn't definitively known, but the two most likely originators are Jöns Jacob Berzelius, who sketched a similar tube around 1820, and Michael Faraday, who referenced one in the 1850s.
What is a Durham tube used for?
A Durham tube is a small inverted test tube placed inside a larger one, used in microbiology since 1898 to visually detect gas produced by fermenting microorganisms.
Why are test tubes used in medical labs?
Specialized test tubes, known as blood collection tubes, are used in medical labs to collect and store blood samples safely for clinical chemistry and diagnostic testing.
