science

Rideal–Walker coefficient

Rideal–Walker 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 Rideal–Walker coefficient rather than just read about it. In short: The Rideal–Walker coefficient, now only of historical interest, is a figure expressing the disinfecting power of any disinfectant. It is the ratio of the dilution of the disinfectant that kills a microorganism to the dilution of phenol that kills the organism in the same time under identical conditions.

Key takeaways

Rideal–Walker 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 Rideal–Walker coefficient to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Rideal–Walker coefficient from memory before moving on to harder problems.

Reference excerpt

The Rideal–Walker coefficient, now only of historical interest, is a figure expressing the disinfecting power of any disinfectant. It is the ratio of the dilution of the disinfectant that kills a microorganism to the dilution of phenol that kills the organism in the same time under identical conditions. The Rideal–Walker coefficient determines the phenol coefficient utilizing the method (test) described by English chemists Samuel Rideal (1863–1929) and J. T. Ainslie Walker (1868–1930). The arbitrary choice of contact time (sterilisation in 7.5 minutes), diluent (distilled water) and test organism (Salmonella typhi, then called Bacillus typhosa) did not reflect the conditions under which disinfectants were used. Because of this, impossibly high values were obtained for disinfectant activity and quoted by disinfectant manufacturers. The method was referred to by distinguished microbiologist Sir Ashley Miles as "...at best a grossly over-simplified answer to a very difficult problem, and at worst little short of bacteriological prostitution". It was replaced by a more realistic test devised by Dame Harriette Chick and Sir Charles James Martin, which in turn was replaced by other tests, not reliant on a comparison with phenol, in attempts to assess the effectiveness of particular disinfectants for different purposes.

Worked examples

Example 1 — a first encounter with Rideal–Walker coefficient

Start with the simplest possible case. Write down what Rideal–Walker 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 Rideal–Walker 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 Rideal–Walker 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 Rideal–Walker coefficient

In research: Rideal–Walker 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 Rideal–Walker 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: Rideal–Walker coefficient is common in secondary-school and first-year university syllabi. It links to neighbouring topics Disinfectants, so understanding it makes those chapters shorter.
In everyday life: Look for Rideal–Walker 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 Rideal–Walker coefficient in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Rideal–Walker 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 Rideal–Walker coefficient out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Rideal–Walker coefficient in simple terms?

Why does Rideal–Walker 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 Rideal–Walker 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 Rideal–Walker coefficient.