How Obtained - Quantity and Kind of Acid Used - Its Purification Necessary - The Purifiers and How Used - Chemical Purification - Filtration - Filtration and Chemical Purification - Chemical Impurities and Remedies - Application of Remedies - Examination of Carbonic Acid Gas.

How Carbonic Acid Gas Is Obtained

Carbonic acid gas is obtained by the chemical action of sulphuric acid or muriatic acid on the carbonates. The acids having greater affinity than carbonic acid for the alkalies unite with it and displace the carbonic acid, setting it free in gaseous form.

All carbonates must be mixed with water and be in a state of fine division. The carbonates in a powdered condition offer a larger surface to the acid for its action, and thus a more thorough exhaustion may be expected. Never bring the carbonates in their dry state in connection with the acids. This would cause a sudden evolution of gas, a blocking up of connecting pipes, and the carbonate would get but partially decomposed. As the conversion of water into steam produces pressure in the boiler, so the conversion of solid carbonic acid into gas in a generator produces pressure. Advantage is taken of the pressure thus produced to assist the combination of the water and gas, in the apparatus of the American plan.

About the quantity of water necessary to mix with the carbonates, there are no positive rules; it depends entirely upon the kind of material used. Generally the carbonates are mixed with double their quantity of water by measure, viz.: 5 gallons of marble dust or whiting, powdered or ground, mixed with 10 gallons of water.

When a powdered or ground carbonate is used, the necessary quantity of water is put first into the generator, and the carbonate added second by means of a wide funnel, constantly turning the agitator to prevent its getting hard, sticking to the bottom or becoming lumpy. When the carbonates are lumps, they are previously mixed and powdered in water and both together poured into the generator.

Limestone we know to be used ground or in fragments - the latter being preferable, when muriatic acid should be used, as the evolution of gas takes place more steadily than in ground state. In the United States limestone ground is used by a few manufacturers and decomposed exclusively with sulphuric acid.