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