The quantity of sulphuric or muriatic acid required for the decomposition of the carbonates depends upon their percentage of carbonic acid.

For the production of 100 parts by weight of carbonic acid are required according to Dr. Hirsch's table theoretically, parts

According to these figures 227 lbs. of marble dust, whiting, etc., need 241 to 244 lbs. of sulphuric or 505 to 555.6 lbs. of muriatic acid of 66° respectively, 21 or 19° Bme - to produce 100 lbs. of carbonic acid, or in other figures: 100 parts by weight of

In practice not so much acid is taken and not so much carbonic acid gas is obtained, as all carbonates contain more or less foreign substances which are indifferent to the action of the acids. It is to be considered that some carbonates are difficult to be entirely decomposed, and it must be remembered that the work is never conducted throughout with perfect accuracy and economy, that some gas remains in generator and purifier, and that some is to be spent in removing atmospheric air from the apparatus.

The proportions generally used in practical carbonating are about 25 pounds of marble dust, or any other carbonate, to 15 pounds of sulphuric acid, or about 5 gallons of marble dust and whiting to 2 1/2 or 3 gallons of sulphuric acid, and 10 gallons of water.

The careful carbonator will soon be enabled to ascertain the practical limit within which his actual and theoretical results should agree. Many manufacturers use the materials in the following proportions:

1 gallon acid, 2 gallons marble dust or whiting, 4 gallons of water, and prefer rather to use the carbonate in excess, which is cheaper than acid.

If the capacity of an apparatus is not quite exactly known, the following rules are generally applied: Measure capacity of acid chamber, use twice as many gallons of marble dust, etc., and double the quantity of water, providing the combined amount of carbonate and water does not exceed 2/3 of the total capacity of generator body.

The generator should never be filled over 2/3 of its capacity; this is important, as space has to be reserved for the down-flowing acid, and room for the generated carbonic acid gas above the surface of the mixture in the generator. If too full, the contents are very apt to boil over and contaminate the liquid in the fountains.

It is worth repeating, that marble dust is the most compact but least effervescent of the carbonates; and as it is by far principally used in the United States, we should give it our particular attention.

Marble dust, like all other carbonates, is insoluble in water, but is mixed with this in order to allow its being easily agitated, and to get it in a state of fine division as already stated. But the quantity of water can be put at an equal quantity, or one and a half of that of the marble dust (1 to 1 or 1 to 2) if the size of generator does not permit more, and the operation will be the same with the exception that the more water the better the heavy marble dust can be agitated.

For whiting (chalk) the same proportions may be used, however, some manufacturers prefer to use rather two or three gallons of water to one of whiting, as it otherwise becomes too soon a thick, pasty mass, and this precaution is well applied where the apparatus offers room enough. Whiting is very effervescent, and the gas therefore has to be very slowly and carefully generated; the flow of acid must be very small and regular to prevent the boiling over of the contents. A great amount of water in generator lessens somewhat this danger, and regulates to a certain extent the evolution of gas, as the acid gets more diluted and the whiting is more in a state of finer division, thus lessening the sudden action of strong acid on a more concentrated carbonate.

The residue ought to be free of undecomposed carbonate, and of an excess of acid. However, an excess of undecomposed carbonate guarantees the exhaustion of the acid better than an excess of acid guarantees the thorough displacement of the carbonic acid. Therefore we prefer rather the use of a small excess of carbonate than of acid, as the latter effects the apparatus, and as the carbonate is cheaper than the acid.