Daniell cell#Gravity cell

The gravity Daniell cell is a group of various advancements of the Daniell element developed in 1836, a historic galvanic cell. Gravity - Daniell elements were used as energy storage, among others in the electrical telegraphy until the early 20th century, they are among the so-called wet-cell batteries.

Construction

As the Daniell cell pass all gravity Daniell elements of two half- cells with a negative electrode of zinc in zinc sulfate solution and a positive electrode made of copper in a copper sulfate solution. Daniell cell in the original two Sulfaltlösungen are separated by a diaphragm also referred to as a salt of conductor which serves as an ion conductor, and in stoneware (alumina) is. Because of this, the diaphragm of the internal resistance of a Daniell cell is about 10 Ω, which element at a voltage of 1.1 V has a maximum discharge current of 100 mA in the range permitted, which is too low for many applications.

To reduce the internal resistance of the high resistance element Daniell diaphragm is omitted and the two brought sulfate solutions in direct contact. In order to prevent unwanted mixing that would lead to failure of the element, the different densities of the two sulfate solutions is exploited to separate, from which the name originates for Gravity gravity. The top of the gravity Daniell elements, the zinc sulphate solution is easier with the zinc electrode, which may be designed as a ring or mesh, such as the dense copper sulfate solution having a copper electrode. This type of galvanic cells had a significantly reduced internal resistance in the range of 1 Ω.

However, these cells are sensitive to vibrations, can be operated in a vertical position, and can be in operation, do not transport with which mobile applications are excluded. Moreover, the absence of a lead diaphragm during prolonged storage of cells to increased diffusion of the two sulfate solutions and to self-discharge. Gravity - cells was therefore collected immediately before startup, and the beaker slowly filled with the sulfate solutions, in order to avoid mixing.

Designs

In sum, there are several different designs of gravity Daniell cell which are named after their developers.

Meidinger element

The Meidinger element, named after the physicist Heinrich Meidinger, is at the bottom of a glass beaker which is filled with copper sulphate solution, labeled with dd in the drawing, which h the internally mounted glass tube and placed at the bottom and upwards isolated guided copper electrode surrounds. In the centrally located inside the glass tube is a reservoir of solid copper sulfate, which can pass into the copper sulfate solution through a small opening at the bottom. The range above, labeled AA, is filled with the lighter zinc sulfate, with zinc electrode located at the top. The glass mug in the lower section also has the task to delay the mixing of the two solutions as long as possible.

The Meidinger element was built in different forms, as shown in the right illustration.

Callaud element

Through the constructive comparatively complicated structure of the glass Meidinger element, the Callaud element was developed around 1860, as shown above, which was used because of its simplicity for decades in Telegrafiebereich. This simplest form of a Gravity - cell consists only of a cup in which the two sulfate solutions are superimposed introduced. The copper electrode is sometimes added in the lower area with a solid copper sulfate crystals in the bottom region of a higher amount of charge, the zinc electrode is located in the top portion and is hooked on the cup edge.

Lockwood element

An improvement of the electrode shape with an increased capacity to provide the Callaud element similarly constructed Lockwood element represents the zinc electrode overhead is executed in solid zinc, at the bottom of the spiral copper electrode is immersed in a reservoir of copper sulfate.

Literature sources

Historic battery
Primary battery

Stoneware#History and notable examples Aluminium–air battery Nickel oxyhydroxide battery Sodium–sulfur battery Nickel–lithium battery Lithium–air battery Lithium–sulfur battery Edison-Lalande cell Grove cell Clark cell

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