science

Phenol coefficient

Phenol coefficient is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Phenol coefficient rather than just read about it. In short: The Phenol coefficient, is now largely of historical interest, although the principles upon which it is based are still used. It is a measure of the bactericidal activity of a chemical compound in relation to phenol.

Key takeaways

Phenol coefficient belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Phenol coefficient to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Phenol coefficient from memory before moving on to harder problems.

Reference excerpt

The Phenol coefficient, is now largely of historical interest, although the principles upon which it is based are still used. It is a measure of the bactericidal activity of a chemical compound in relation to phenol. When listed numerically, the figure expressing the disinfecting power of a substance by relating it to the disinfecting power of phenol may be a function of the standardized test performed. For example, the Rideal–Walker method, introduced in 1903 gives a Rideal–Walker coefficient and the U.S. Department of Agriculture method gives a U.S. Department of Agriculture coefficient. To calculate phenol coefficient, the concentration of phenol at which the compound kills the test organism in 10 minutes, but not in 5 minutes, is divided by the concentration of the test compound that kills the organism under the same conditions (or, probably more common, dividing the dilution factor at which the tested substance shows activity by the dilution factor at which phenol shows comparable activity). The Rideal–Walker test was widely used, but the test conditions chosen were unrealistic, and impossibly high values for the coefficient were claimed by disinfectant manufacturers. Distinguished bacteriologist Sir Ashley Miles, reviewing the subject, described the test as "...at best a grossly over-simplified answer to a difficult problem and, at worst little short of bacteriological prostitution". Modifications were made by Dame Harriette Chick and Sir Charles James Martin in 1908. They used more realistic conditions, including 3% sterile faeces to mimic the conditions in which many disinfectants were used. The Chick–Martin test was then widely used until replaced by more suitable tests not reliant on phenol and reflecting the conditions in which modern disinfectants are used. Calculations by Harriette Chick showed that the killing of bacteria by disinfectants followed first order kinetics. So, the bactericidal activity of a particular disinfectant at a given concentration can be expressed as a constant (k) calculated by employing the formula k = N/C·T where N is the number of surviving cells, C is the concentration of agent applied and T is the time for which the agent is applied, so k is inversely proportional to dose (C·T is collectively called dose). One way to compare disinfectants is to compare how well they do against a known disinfectant and rate them accordingly using the Phenol coefficient. The disinfectant to be tested is compared with phenol on a standard microbe (usually Salmonella typhi or Staphylococcus aureus). Disinfectants that are more effective than phenol have a coefficient greater than 1; those that are less effective have a coefficient less than 1.

References

Dorland's Illustrated Medical Dictionary. 2004. "Phenol c." entry. Archived from the original on November 2, 2006. Retrieved 2006-11-06.

Worked examples

Example 1 — a first encounter with Phenol coefficient

Start with the simplest possible case. Write down what Phenol coefficient claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Phenol coefficient before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Phenol coefficient ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Phenol coefficient

In research: Phenol coefficient appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Phenol coefficient in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Phenol coefficient is common in secondary-school and first-year university syllabi. It links to neighbouring topics Antiseptics, so understanding it makes those chapters shorter.
In everyday life: Look for Phenol coefficient outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Phenol coefficient in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Phenol coefficient means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Phenol coefficient out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Phenol coefficient in simple terms?

Why does Phenol coefficient matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Phenol coefficient?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Phenol coefficient.