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I recently was in need of zinc for an experiment. So I resorted to obtain it from some dry cell. But I wondered if it was pure zinc or was it $\ce{ZnO2}$ or any other compound of $\ce{Zn}$. It then occurred to me that I had knowledge of existence of pure $\ce{Zn}$ and its compounds, but how would its discovery have happened without the prior knowledge of its existence?

How did scientists discover the elements without knowing of their existence and unique properties?

Modern day scientists rely on technology and advanced nuclear physics. But in absence of these advances, how were ancient scientists able to discover them?

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Modern day scientists rely on technology and advanced nuclear physics. But in absence of these advances, how were ancient scientists able to discover them?

In many cases, they weren't - the ancient... maybe we can't call them scientists. Let's call them "natural philosophers." The ancient natural philosophers (up until about 1700) only knew about a handful of elements. This is part of the reason that it took so long to put the periodic table together.

At the time, an element was something that was not reducible to smaller components. The ancient philosophers tended to conflate properties of things with this idea of fundamental components, and as a result, things like earth, air, fire, and water were thought of as elements. When we say they "knew about" modern elements, what we mean is that they knew of the substances - they did not necessarily know that they were chemical elements in the sense that we define them today.

That modern concept of an element defined by the number of protons in the nucleus wasn't developed until around 1913. The wikipedia article on the history of chemical element definitions gives a good overview of how the definition has evolved over time.

The time period you are probably most interested in is that between the "ancient" era (pre-history up until the mid-1660's or so) to the beginnings of the modern era (say early 1900's). During this period, chemistry was evolving from alchemy into a modern science. The systematic investigation and communication of results was occurring, and a large body of known but poorly understood chemical "recipes" was available to chemists. Using a range of reactions and isolation techniques, they basically just randomly tried things (maybe not completely randomly) until they reached a point where it seemed like something could not be decomposed further, or until they identified a new substance. In many cases, they would discover the new element, but not be aware that it was an element - in other words, they could isolate and identify a substance, but because our collective understanding of chemistry was still very limited, they had no way of knowing that it was an elemental substance.

Wikipedia's list of elemental discoveries gives details about the discovery of each element - although you should keep in mind that "discovery" in this case means "identified as a new substance," not necessarily "identified as a chemical element."

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Essentially, a continuous process of trying to find the purest forms of different materials, and then find patterns and distinctions in how they behave.

For example: say you pick up a random rock. You can try to measure as many qualities as possible about it: colour, hardness, density, magnetic susceptibility, and so on. Then, try to make it into something else. Heat it, freeze it, attack it with acids, water, alkali, and see if it seems to behave like anything you already know about, or whether you can convert it into something that does.

The more methods you have, the more sure you can be that two different objects are composed of the same material, or different materials. Particular similarities can cause problems, for example it took a long time for people to manage to separate the lanthanides because they behave very similarly under many tests.

In some cases, elements have also discovered after finding unexpected results -- for example, helium was discovered in the spectral lines of the sun's radiation before it was ever isolated or identified on Earth.

It's a common problem of trying to find the irreducible complexity behind an opaque emergent system -- in this case, trying to work back from the materials we have to their fundamental components. The more information you have, the easier it is to discern more elemental qualities and patterns, and the more other bits you can find.

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Zinc doesn't naturally occur in elemental form. Instead, it occurs as zinc sulfide.

It is thought that zinc was first produced in India and China by roasting the zinc sulfide with a carbon reducing agent, possible dung.

Zinc is a component of brass. Zinc was first produced as this alloy with copper.

Purer forms of zinc were first produced in Rajasthan by distillation.

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Many metals are unstable in their elemental form and naturally form oxides. Scientists from the 1600s and 1700s believed these metal oxides to be a substance called “phlogiston” until oxygen was discovered by Antoine Lavoisier ( and Joseph Priestly). After that more elements were rapidly discovered.

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