It comes from the Greek ? or ? (Kappa) developed from the Semitic Kap, symbol for an open hand. This in turn was likely adapted by Semites who had lived in Egypt, from the hieroglyph for "hand" representing D for the Egyptian word for hand, d-r-t. The Semites evidently assigned it the sound value /k/ instead, because their word for hand started with that sound.

The Semitic value of /k/ was maintained in most classical as well as modern languages, although Latin abandoned the use of K almost completely, preferring C. When Greek words were taken into Latin, the Kappa was converted to C; Latin used K for other languages such as Etruscan, as seen in words such as kalendae, "first day of the month", whence English calendar. Some words from other alphabets were also transliterated into C. Therefore, the Romance languages have K only in words from still other language groups. The Celtic languages also chose C over K, and this influence carried over into Old English. Today, English is the only Germanic language to productively use hard C in addition to K (although Dutch uses it in learned words of Latin origin and follows the same "hard/soft" distinction in such words as does French and English -- but not in native words).

A soft, silver-white, highly or explosively reactive metallic element that occurs in nature only in compounds. It is obtained by electrolysis of its common hydroxide and found in, or converted to, a wide variety of salts used especially in fertilizers and soaps. Atomic number 19; atomic weight 39.098; melting point 63.65°C; boiling point 774°C; specific gravity 0.862; valence 1.

A deficiency of potassium in the blood is referred to as hypokalemia and manifests itself in many ways. Among the most serious are arthritis, high blood pressure, heart disease, stroke, cancer, and even infertility, as potassium constitutes a vital element of seminal fluid.

Potassium deficiency will increase acid levels in the body, lowering the natural pH, which will have far reaching effects. Lack of potassium can also aggravate problems caused by lack of protein. If potassium levels are down, the liver cannot operate normally, particularly regarding transformation of glucose to glycogen. A healthy liver should have about twice as much potassium as sodium.

Potassium deficiency can cause problems with the formation of connective tissue, and can render normally strong body tissue vulnerable to all kinds of problems. The collagen of a healthy person is approximately as strong as steel, and the strength of bone tissue can be likened to that of cast iron. Lack of potassium may create a susceptibility to fractures, skin lesions that do not heal, or other connective tissue problems. So important is potassium for the protection of collagen that many natural health gurus claim that along with other vital nutrients, it constitutes an essential element of protection against premature aging. As long ago as the 1920s, Max Gerson was the first person ever to cure lupus lesions with a diet designed to reduce abnormally high sodium levels and raise potassium levels to normal, which was entirely raw fruit and vegetables.

Potassium is essential to the efficient processing of foods in the body; without it they cannot be broken down into the proper compounds. This can lead to rheumatism, and is one reason why adequate potassium prevents rheumatism.

El kelvin es la unidad de temperatura de la escala creada por William Thomson, sobre la base del grado Celsius, estableciendo el punto cero en el cero absoluto (-273,15 °C) y conservando la misma dimensión. William Thomson, quién más tarde sería Lord Kelvin, a sus 24 años introdujo la escala de temperatura termodinámica, y la unidad fue nombrada en su honor.

Se toma como la unidad de temperatura en el Sistema Internacional de Unidades y se corresponde a una fracción de 1/273,16 partes de la temperatura del punto triple del agua. Se representa con la letra "K", y nunca "ºK". Además, su nombre no es el de "grado kelvin" sino simplemente "kelvin"; no se dice "19 grados Kelvin" sino "19 kelvin" o "19 K". Adelante Kelvin

Coincidiendo el incremento en un grado Celsius con el de un Kelvin, su importancia radica en el 0 de la escala: a la temperatura de 0 K se la denomina cero absoluto y corresponde al punto en el que las moléculas y átomos de un sistema tienen la mínima energía térmica posible. Ningún sistema macroscópico puede tener una temperatura inferior. A la temperatura medida en Kelvin se le llama "temperatura absoluta", y es la escala de temperaturas que se usa en ciencia, especialmente en trabajos de física o química.

También en iluminación de vídeo y cine se utilizan los kelvin como referencia de la temperatura de color. Cuando un cuerpo negro es calentado emitirá un tipo de luz según la temperatura a la que se encuentra, por ejemplo 1600 K es la temperatura correspondiente a la salida o puesta del sol. La temperatura del color de una lámpara de filamento de tungsteno corriente es de 2800 K. La temperatura de la luz utilizada en fotografía y artes gráficas es 5000 K y al del sol al mediodía con cielo despejado es de 5200K. La luz de los días nublados es más azul y es de más de 6000 K.