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m the oxygen of an inclosed portion of air by causing that gas to unite with phosphorus. Place a piece of phosphorus the size of a pea in a depression in a flat piece of cork. (Handle phosphorus with wet fingers or with forceps.) Place the cork on water and have ready a glass fruit jar holding not more than a quart. Ignite the phosphorus with a hot wire and invert the jar over it, pushing the mouth below the surface of the water. The phosphorus uniting with the oxygen fills the jar with white fumes of phosphoric oxide. These soon dissolve in the water, leaving a clear gas above. This is nitrogen. Place a cardboard under the mouth of the jar and turn it right side up, leaving in the water and keeping the top covered. Light a splinter and, slipping the cover to one side, thrust the flame into the jar of nitrogen, noting the effect. (Flame is extinguished.) Compare nitrogen with oxygen in its relation to combustion. What purpose is served by each in the atmosphere? _Oxygen._--Review experiments (page 114) showing the properties of oxygen. _Phosphorus._--Examine a small piece of phosphorus, noting that it has to be kept under water. Lay a small piece on the table and observe the tiny stream of white smoke rising from it, formed by slow oxidation. Dissolve a piece as large as a pea in a teaspoonful of carbon disulphide in a test tube, pour this on a piece of porous paper, and lay the paper on an iron support. When the carbon disulphide evaporates the phosphorus takes fire spontaneously. (The heat from the slow oxidation is sufficient to ignite the phosphorus in the finely divided condition.) What is the most striking property of phosphorus? What purpose does it serve in the match? _Sulphur._--Examine some sulphur, noting its color and the absence of odor or taste. (Impure sulphur may have an odor and a taste.) Burn a little sulphur in an iron spoon, noting that the compound which it forms with oxygen by burning has a decided odor. _Other Elements._--_Magnesium._ Examine and burn a piece of magnesium ribbon, noting the white compound of magnesium oxide which is formed. _Iron._ Examine pieces of the metal and also some of its compounds, as ferrous sulphate, ferric chloride, and ferric oxide or iron rust. _Sodium._ Drop a piece of the metal on water and observe results. Sodium decomposes water. It has to be kept under some liquid, such as kerosene, which contains no oxygen. (It should not be touched except with the finge
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