CARBON DIOXIDE. The popular belief that poisoning from carbon dioxide occurs in unventilated and overcrowded rooms is a mis taken one. Results observed on such occasions are due in large part to the reduction in the amount of oxygen present and not to the in crease of carbon dioxide, which in no sense is a poison, but which is frequently confounded with carbon monoxide, one of the deadliest of poisons.
Commercial Methods of Manufacture.— Carbon dioxide is extracted from natural sources at many places in Europe and at Sara toga Springs, N. Y. Its origin is debatable but is generally considered to be volcanic and it is obtained by sinking wells from which the gas issues as such, or combined with saline water. A purity of less than 98 per cent is not commercially satisfactory and if a "dry gas' well does not come up to this the desired purity is generally obtained by sinking to greater depths. Failing this the impure gas must be treated by absorption as described under the coke process.
Where the gas occurs, as at Saratoga Springs, saturating the escaping spring water in proportions as high as five volumes of gas to one of water, its recovery is a simple matter. The pipe carrying the saturated spring water delivers its burden to a separator whose trapped water outlet offers greater resistance than the water seal of the storage gasometer, with the result that the water flows away, holding only that amount of gas due to atmospheric pressure and temperature of emergence — about equal volumes of gas and water — and the surplus gas is piped from the top of the separator to the gasometer.
If, as sometime. occurs, hydrogen sulphide is present, its removal is effected before storage of the gas by passing it through trays filled with iron oxide mixed with wood shavings. After saturation the oxide is revivified by exposure to air.
The natural carbon dioxide at Saratoga Springs has a purity of about 98.5 per cent and in common with gas of like origin from several other sources has been found to be radio-active.
A process for manufacture of carbon dioxide which has been largely displaced depends upon the calcination of magnesite (carbonate of magnesia). The rock, crushed to suitable fine ness, is fed to oil-fired retorts, and carefully held at the proper temperature. The escaping gas, passed if necessary through purifiers for removal of traces of sulphur compounds, and then through coolers, is conveyed to the gas ometer while the calcined magnesia, containing always more or less unburnt magnesite, is al lowed to cool, ground and sold as a by-product.
Its value is largely affected by the care with which the calcination is conducted and by the presence of calcium salts which are highly de leterious for certain uses. Until the develop ment of the California deposits, the chief source of supply was Grecian. Importations from that source were suspended early in the war.
A small amount of carbon dioxide is pro duced by plants engaged in the manufacture of epsom salts. The process is purely the labora tory one on a large scale, of adding an acid, sulphuric, to a carbonate, magnesite. There is, however, a variation, wherein dolomite, a mixed carbonate of magnesia and lime, is treated with sulphuric acid and the resulting mixed sulphates separated. In both cases the carbon dioxide obtained is of high purity and passes to the gasometer without further treat ment. The normal demand for epsom salts is not such as to stimulate production along these lines.
A small amount of carbon dioxide has been produced 'in the manufacture of beer, but the advent of prohibition has closed this avenue. Such great difficulties were found in removal of odorous products of fermentation that gas from this source never became a product of import ance.
The coke process is the one most generally used in the commercial production of carbon dioxide. Substantially it involves the com bustion of coke with effort to secure as high a percentage of carbon dioxide as possible in the resulting gaseous products. These are passed through scrubbers and thoroughly washed to ensure removal of any sulphur compounds, and then enter the absorbing towers. These are generally of steel, about eight feet in diameter and 50 feet high and of any desired number, depending on the capacity of the plant. In general about 10 cubic feet tower capacity per pound carbon dioxide per hour is accepted as a suitable distributing proportion. The gases are there brought in contact with a solution of car bonate of soda or potash which is pumped to the top and flows counter-current against the gases.