Modern Gasworks Practice

GAS-MAKING AND OTHER COALS 363 As regards gas-making yields a high, quality cannel is capable of giving, in exceptional cases, 14,000 cubic feet of gas, with. an illuminating power of from 35 to 45 candles. Cannel tar is of a distinctly paraffinoid nature. In recent years cannel coals and shales have mainly attracted attention from the point of view of oil production, and during the war extensive experiments were carried out with. this purpose in. view. SPACE OCCUPIED BY COALS, ETC. For the purpose of estimating stocks of coal or coke it is necessary to have some idea of the space occupied per unit of weight by various solid substances. For the use of the gas engineer the following figures will be found suitable, but the physical condition of the material may account .for some variation in either direction :— 1 Ton of— Ordinary gas coal (unbroken) occupies . . 42 . 35 . 35 . 85 to 43 cubic feet. „ „ (broken) Cannel coal (vanes considerably) Anthracite Coke (unbroken) 99 9 9‘ • „ • 55 40 to 45 99 99 99 99 99 99 99 99 99 39 92 Breeze J, • . 60 99 65 99 99 Lime (1 yard = 12} cwts.) 42 99 99 Oxide of iron (Dutch) » • 45 99 99 „ „ (Prepared) ?> • 41 99 99 „ „ (Belgian) 99 • 40 99 99 Sulphate of ammonia 99 • . . . 47 to 48 99 99 CONSIDERATIONS AFFECTING THE PURCHASE OF COAL It is extremely difficult to lay down any hard and fast stipulations on which. to base the purchase of coal intended for gas-making purposes. A final clioicé should not necessarily be influenced by a comparison of thermal units per ton and total residuals, but by a consideration of net financial standing after all charges have been balanced against receipts. It is for this reason tliat many concerns still adhere to the poorer classes of coal where the collieries producing these are near the gasworks, thus saving in freightage charges. High yields of gas per ton are undoubtedly alluring, but useful contrasts between the working results of different gasworks cannot be drawn on this basis. The only true gauge is the annual or half-yearly balance-sheet. Coal for all the larger gasworks is purchased by contract, usually for a period of twelve montiis. In the ordinary way these contracts are entered into as dating from Ist July in each year, for a specified monthly quantity. In the majority of cases a fixed yearly price is settled, but occasionally a somewliat higher price for the six winter months has to be conceded. The various coal groups have by this time established a reputation, either good or indifferent, for the dass of material they turn, out; and as each. dist-rict or series of seams has its own particular name, the name alone is often sufficient to convince the purchaser of what he is buying. For all that, coals occurring in the same locality vary considerably, and too mucli