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Kipp's apparatus

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A Kipp's apparatus is a specialized laboratory tool used to prepare small volumes of gas.

Kipp Apparat
Kipp Apparat

This device allows a chemist to control the production of gas by regulating a chemical reaction. It was invented around 1844 by a Dutch pharmacist named Petrus Jacobus Kipp. For many decades, it was a common sight in chemical laboratories and school demonstrations. Today, most laboratories have moved away from using this apparatus. Instead, they use industrial gas cylinders to supply their needs. These cylinders provide gases that are much purer and drier than those produced by a Kipp generator.

Kipp apparatus
Kipp apparatus

The physical design of the apparatus is quite distinct. It is typically constructed from glass, though some versions are made of polyethylene. The structure consists of three vertically stacked chambers that resemble the shape of a snowman. A tube extends downward from the upper chamber, passing through the middle chamber and into the bottom chamber. Between the middle and lower chambers, there is a retention plate. This plate is often a conical piece of glass containing small holes. These holes are designed to permit the passage of both liquid and gas while holding solid materials in place.

Operating the apparatus requires a specific sequence of steps to manage the reaction. To begin, a solid material, such as iron sulfide, is placed into the middle chamber. These solids must be in lumps large enough to stay above the retention plate. Next, a liquid, such as an acid, is poured into the top chamber. The acid can flow down the tube into the bottom chamber, but it cannot rise back up unless the gas pressure allows it. To start the process, a user opens a stopcock, which is a small valve located near the top of the middle chamber. Opening this valve lets air escape, allowing the liquid to flow through the retention plate and reach the solid material.

Once the liquid and solid meet, a chemical reaction occurs, and gas is evolved. This gas can be drawn off through the stopcock as needed. The apparatus has a built-in mechanism to stop the reaction automatically. When the stopcock is closed, the pressure of the evolved gas in the middle chamber begins to rise. This increasing pressure pushes the liquid back down into the bottom chamber. Once the liquid is no longer in contact with the solid material, the reaction stops. This cycle allows for precise, on-demand production of gas. However, this method only works if the solid material is insoluble in the acid. If the solid were to dissolve, gas would continue to evolve even after the liquid level dropped.

Scientists have used the Kipp's apparatus to produce a vast array of different gases. For example, hydrogen can be generated using iron flakes or zinc combined with hydrochloric or diluted sulfuric acid. Carbon dioxide is produced by reacting pieces of marble, which is calcium carbonate, with hydrochloric acid. Other complex gases include hydrogen sulfide, made from iron(II) sulfide and acid, and acetylene, made from calcium carbide and water. The apparatus can even produce methane from aluminium carbide and lukewarm water. It can also be used to make more specialized substances like ozone, ammonia, and various silanes or germanes.

Because the gas is produced through a vigorous chemical reaction, it is often not ready for immediate use. The produced gas is frequently contaminated with water vapor or a fine aerosol of the reacting chemicals. Therefore, the gas often requires further purification or drying. For instance, acidic gases like hydrogen chloride or sulfur dioxide can be dried using concentrated sulfuric acid or phosphorus pentoxide. Basic gases, such as ammonia, can be dried using substances like calcium oxide or sodium hydroxide. This extra step ensures the gas reaches the required purity for scientific experiments.

Beyond simple gas production, the apparatus has several historical and specialized variations. One interesting version is the Döbereiner's lamp, which is a small, modified Kipp's apparatus used to produce hydrogen. In this version, the hydrogen is passed over a platinum sponge catalyst. The reaction between the hydrogen and oxygen in the air heats the catalyst, creating a gentle flame. This device was commercialized in the 1820s for lighting pipes and fires, with over a million units sold. Other larger variants, such as those designed by Gay-Lussac and Verkhovsky, were created to produce much larger amounts of gas than the standard Kipp generator.

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