The oval-shaped zero and circular letter O came into use together on modern character displays. The zero with a dot in the centre seems to have begun as a choice on IBM 3270 controllers (this has the problem that it looks like the Greek letter theta). The slashed zero, looking like the letter O with a diagonal line drawn inside it, is used in old-style ASCII graphic sets that came from the default typewheel on the well-known ASR-33 Teletype. This format causes problems because it looks like the symbol formula_1, representing the empty set, as well as for certain Scandinavian languages which use Ø as a letter.
The rule which has the letter O with a slash and the zero without was used at IBM and a few other early mainframe makers; this is even more of a problem for Scandinavians, because it looks like two of their letters at the same time. Some Burroughs/Unisys computers display a zero with a backwards slash. And yet another convention common on early line printers left zero without any extra dots or slashes but added a tail or hook to the letter O so that it resembled an inverted Q or cursive capital letter O.
The letters used on some European number plates for cars make the two symbols look different. This is done by making the zero rather egg-shaped and the O more circular, but most of all by cutting open the zero on the upper right side, so the circle is not closed any more (as in ). The style of letters chosen is called "" (abbr.: "FE Schrift"), meaning "script which is harder to falsify". But those used in the United Kingdom do not make the letter o and the number 0 look different from each other, because there can never be any mistake if the letters are correctly spaced.
In paper writing you do not have to make the 0 (zero) and O (letter O) look different at all. Or you may add a slash across the zero in order to show the difference.
Functions are explained in the Function (mathematics) article. If the function "f"("x") = 0, then "x" is called a zero (or root) of the function "f". For example, if the function "f"("x") is "x" − 1, then the zeroes of the function are +1 and −1, because "f"(+1) = (+1) − 1 = 0, and "f"(−1) = (−1) − 1 = 0.
Zeroes of a function are used because they are another way to talk about solving an equation, which is a main goal in algebra. If we want to solve an equation like "x" = 1, then we can subtract the right-hand side of the equation from both sides, in this case 1. Whatever we get on the left-hand side, in this case "x" − 1, can be called a function "f"(x). The right-hand side has to be zero, because we subtracted it from itself. So "f"(x) = 0. Finding the zeroes of this function is the same as solving this equation. In the paragraph before, the zeroes of this function are +1 and −1, so they are the solutions of this equation. We got this equation by subtracting the same thing from both sides, so we also have solutions to the equation we started with, in this case "x" = 1. More generally, if we could find zeroes of functions, we could solve any equation.
Zoology
Zoology is the science of studying animal life. It is part of biology. The word is pronounced "Zō-ölogy", not "Zoo-ology". Animal life is classified into groups called phyla, of which there are at least thirty.
Zoologists are scientists who study animals. They may work in laboratories, or do field research. The methods are many and various. At the heart, they cover the structure, function, ecology and evolution of animals. The structure is investigated by dissection, and microscopic examination. The function is investigated by observation and experiment. Palaeontology supplies information about extinct animals. Zoologists may be employed by universities, museums, or by zoos.
Some zoologists:
Zinc
Zinc, sometimes called spelter, is a chemical element. It is a transition metal, a group of metals. It is sometimes considered a post-transition metal. Its symbol on the periodic table is "Zn". Zinc is the 30th element on the periodic table, and has an atomic number of 30. Zinc has a mass number of 65.38. It contains 30 protons and 30 electrons. In total, 29 isotopes of zinc are known, and five of these occur in nature. Some isotopes are radioactive. Their half-lives are between 40 milliseconds for Zn and 5x10 years for Zn.
Zinc is a metal that is mostly used for galvanizing and batteries. It is the fourth most common metal.
Zinc is a shiny bluish grey metal. When it has just been cut, zinc has a whitish-grey color. If it is exposed to air, it will not stay shiny for long. Its melting point is at (), boiling point is (), cooling point is at , and freezing point is at . This temperature is lower than most transition metals but higher than tin or lead. It can be melted on a cooking stove. It boils at a low temperature for a metal. It is not magnetic. When heated a little, it becomes very flexible. If it is heated more, it becomes very brittle. It forms alloys easily with other metals.
Zinc is a reactive metal. It is about as reactive as aluminium and more reactive than most of the more common metals, such as iron, copper, nickel, and chrome. It is less reactive than magnesium. Zinc can react with acids, bases, and nonmetals. It does not rust in air, though. A coating of zinc oxide and zinc carbonate forms on the surface of the zinc when it is in air. This coating stops corrosion. Acids can dissolve this coating and react with the zinc metal. This reaction of zinc with an acid makes a zinc(II) salt such as zinc chloride and hydrogen gas. This is a very common chemical reaction. The reaction below is the reaction with hydrochloric acid.
Zinc can burn when powdered or in small pieces to make zinc oxide, a white powder. The flame is bright blue-green.
Zinc oxide can dissolve in strong bases. This reaction happens in some batteries that have zinc in them.
Zinc is a chalcophile. This means that it would rather react with sulfur and elements below it on the periodic table than oxygen. That is why zinc sulfide is the most common zinc ore, not zinc oxide.
Zinc can make chemical compounds with other elements. These chemical compounds are only in one oxidation state: +2. A +1 compound has been found but it is hard to make. There are no other oxidation states other than +1 or +2. Most of these compounds have no color. If they have a color, it is not the zinc that is making the color.
Zinc chloride is one of the most common zinc compounds. They are quite unreactive. They are a little acidic when dissolved in water. They make a green flame when heated in a fire.
Other zinc compounds are:
Five isotopes of zinc are found in nature. Zn is the most common isotope, with 48.63% of naturally occurring Zinc. This isotope has a half-life of 4.3x10 years. This is so long, that its radioactivity can be ignored. Similarly, (0.6%), with a half life of 1.3x10 years is usually considered to not be radioactive. The other isotopes found in nature are (28%), (4%) and (19%).
Zinc is not found as a metal in the earth's crust. Zinc is only found as zinc compounds. Sphalerite, a mineral that is made of zinc sulfide, is a main ore of zinc. Very little zinc is in the ocean. Zinc ore is normally found with copper and lead ores.
There are some other zinc ores, such as smithsonite (zinc carbonate) and a zinc silicate mineral. They are less common.
The zinc sulfide is concentrated by flotation. There is a detergent that collects the zinc sulfide. The impurities sink to the bottom and are removed. Then the zinc sulfide is heated in air to make zinc oxide and sulfur dioxide.
The sulfur dioxide is oxidized to sulfur trioxide.
The sulfur trioxide reacts with the zinc oxide to make zinc sulfate. This makes a soluble form of zinc which can be processed more.
The zinc sulfate is purified and electrolyzed. This electrolysis makes oxygen, zinc, and sulfuric acid. This makes a pure zinc that is known as "SHG" or special high grade.
The sulfuric acid is reused in place of the sulfur trioxide to leach more zinc oxide.