he crayon, and fill the cavity with powdered sulphur. Ignite the
sulphur in the flame of an alcohol lamp or Bunsen burner, and lower it
into a bottle of oxygen. Observe the change in the rate of burning, the
color of the flame, and the material formed in the bottle by the burning.
The gas remaining in the bottle is sulphur dioxide (SO2), formed by the
_uniting_ of the sulphur and the oxygen.

4. Bend a small loop on the end of a piece of picture wire. Heat the loop
in a flame and insert it in some powdered sulphur. Ignite the melted
sulphur which adheres, and insert it quickly in a bottle of oxygen.
Observe the dark, brittle material which is formed by the burning of the
iron. It is a compound of the iron with oxygen, similar to iron rust, and
formed by their uniting.

*Preparation and Properties of Carbon Dioxide.*--1. (_a_) Attach a piece of
carbon (charcoal) no larger than the end of the thumb to a piece of wire.
Ignite the charcoal in a hot flame and lower it into a vessel of oxygen.
Observe its combustion, letting it remain in the bottle until it ceases to
burn. Note that the burning has consumed a part of the carbon and has used
up the free oxygen. Has anything been formed in their stead?

(_b_) Remove the charcoal and add a little limewater. Cover the bottle
with a piece of cardboard, and bring the gas and the limewater in contact
by shaking. Note any change in the color of the limewater. If it turns
white, the presence of carbon dioxide is proved.

2. Burn a splinter in a large vessel of air, keeping the top covered. Add
limewater and shake. Note and account for the result.

3. Place several pieces of marble (limestone) in a jar holding at least
half a gallon. Barely cover the marble with water, and then add
hydrochloric acid until a gas is rapidly evolved. This gas is carbon
dioxide.

(_a_) Does it possess color?

(_b_) Insert a burning splinter to see if it supports combustion.

(_c_) Place a bottle of oxygen by the side of the vessel of carbon
dioxide. Light a splinter and extinguish the flame by lowering it into the
vessel of carbon dioxide. Withdraw immediately, and if a spark remains on
the splinter, thrust it into the bottle of oxygen. Then insert the
relighted splinter into the carbon dioxide. Repeat several times, kindling
the flame in one gas and extinguishing it in the other. Finally show that
the spark also may be extinguished by holding the splinter a little longer
in the carbon dioxide.