Chalk is made by uniting carbonic acid gas with lime; it may therefore be employed as a source of the gas, by placing a few lumps of chalk, or marble, or limestone, in a bottle such as was used in the generation of hydrogen gas; on the addition of some water and hydrochloric acid, effervescence takes place from the escape of carbonic acid gas, and the cork and pewter pipe being adapted, it may be conveyed by its own gravity into glasses, jugs, or any other vessels, and a pneumatic trough will not be required. Carbonic acid gas has a specific gravity of 1.529, and is therefore rather more than half as heavy again as atmospheric air. _Sixth Experiment._ In order to satisfy the mind of the operator that the gas obtained from chalk is similar to the _product of combustion from the diamond_, some lime-water may be placed in a glass, and the gas from the bottle allowed to bubble through it; instantly the same milkiness is apparent, which again vanishes on the addition of acid. And this experiment is rendered still more striking if a lighted taper be placed in the glass just after the addition of the acid, when it will be immediately extinguished. _Seventh Experiment._ If a lady's muff-box, supported by threads or chains, is hung on one end of a scale-beam, and counterbalanced by a scale pan and a few shot, it is [Page 156] immediately depressed on pouring into the muff-box a quantity of carbonic acid gas, which may have been previously collected in a large tin vessel. After showing the weight of the gas, the box is detached from the scale-beam, and the contents poured upon a series of lighted candles, which are all extinguished in succession. (Fig. 147.) [Illustration: Fig. 147. A. Carbonic acid gas poured out of the tin box into B, the muff-box. B B. Detached muff-box, and candles extinguished by the carbonic acid gas poured from it.] _Eighth Experiment._ The property of carbonic acid gas of extinguishing flame, as compared with the contrary property of oxygen, is nicely shown by first passing into a large and tall gas jar one half of its volume of oxygen gas; a large cork perforated with holes may be introduced, so as to float upon the surface of the water in the gas jar, and is usefully employed to break the violence with which the carbonic acid enters the gas jar, as it is passed in to fill up the remaining half volume of the gas jar, which now contains oxygen at the top, and carbonic acid gas at the bottom. On testing the contents of the jar with a lighted taper, it burns fiercely in the oxygen, but is immediately extinguished in the [Page 157] carbonic acid gas, being alternately lighted and put out as it is raised or depressed in the gas jar. _Ninth Experiment._