Modern Gasworks Practice

586 MODERN GASWORKS PRACTICE prepared by mixing together about 1 ton of ground copperas with an equal amount of lime, care being taken to ensure that the lime is present in sufficient quantity to make the mixture alkaline. (3) The trace of sulphuretted hydrogen may be due to Chemical action in the gasholder. The cause of and remedy for such derangements are discussed in the next chapter (see page 688). Purifying Capacity of Material One ton of good quality (Dutch) bog-ore may be considered capable of removing the sulphuretted hydrogen from two to two and a half million cubic feet of gas before it is finally sperrt. The quantity of lime required to extract carbon dioxide varies. in accordance with the amount of inert matter or “ core ” present in the lime. In the usual way, from 3| to 4 yards are necessary per million cubic feet of gas. In the case of lime purification methods for complete removal of all impurities from the gas (i.e. when lime is used in corrjunction with oxide), the quantity of lime may amount to 5| cubic yards per million cubic feet of gas. Basis of Purchase Purifying material in this country is generally purchased on the basis of analysis, i.e. so much per ton for a certain percentage of ferric oxide, with pro rata additions or reductions in accordance with the result of the test. The spent material is sold in accordance with its sulpliur content, i.e. so many pence for each unit (or per cent.) of sulpliur. For example, it may be assumed tliat a spent oxide contains 50 per cent, of free sulpliur, i.e., 50 units per ton. If the price per unitis 9<Z., the value of the oxide is (50 X 9d) = 450Æ, or 37s. 6d. per ton. Small works frequently obtain their oxide on a Ioan basis, paying (say) a penny per ton of coal carbonized, and returning the spent material, when it has reached a certain sulphur content, to the supplier. As bog-ore and other purifying materials are frequently bought subject to certain conditions—particularly with regard to their content of ferric oxide or ferric hydrate—the following contract form, which. may be adopted as a standard, has been included, in the belief that it may prove of some value to gas engineers having the purchase of oxide in view. Specification and Form of Tender for Oxide of Ikon Description—The tender must state the description of material to be supplied. Quantity—The quantity of material required is . . . tons. Moisture—The moisture is not to exceed 50 per cent, by continued hcating at 212° F. Ferric Oxide—The quantity of ferric oxide (i.e. Fe2O3, inclusive of Fe2O3 as FeO) is to be not less than 25 per cent, in the material (in the natural state). Price—The tender is to be at a rate per unit of ferric oxide (Fe2O3, inclusive of Fe2O3 as FeO) per ton in the condition as supplied. Delivery—(As required). Notice of Arrival—A. week’s notice of probable time of delivery should be given by seller to buyer.