*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. (_d_) Tip the jar containing the carbon dioxide over the mouth of a tumbler, as in pouring water, though not far enough to spill the acid, and then insert a burning splinter in the tumbler. Account for the result. Inference as to the weight of carbon dioxide. [Fig. 59] Fig. 59—*Simple apparatus* for illustrating passage of oxygen through the body. (_e_) Review experiments (page 101) showing the presence of carbon dioxide in the breath.