Modern Gasworks Practice

PLANNING AND LA YING OUT OF GAS WORKS 11 the annual charges for construction, working and incidental costs payable to the railway Company. (b) The level of the ground should be low in comparison with the districts to be supplied. It is a “ golden rule ” of gas engineering never to erect a gasworks on a hill. Owing to its specific gravity (0'42 to 0’52, depending on the proportion of carburetted or blue water gas), gas exerts its pressure upwardly; hence where the works is erected on elevated ground unnecessary pressure has to be sacri-flced in driving the gas downwards to consumers. With regard to the so-called loss in pressure, this is usually estimated by an arbitrary rule based on general circum-stances and inclusive of friction in the mains. The rule prescribes that the loss due to altitude will amount to approximately one inch of water pressure for every 100 feet rise in elevation. Gas pressures, as usually understood, are, of course, not absolute; that is to say, they do not start from zero, but from atmospheric pressure as measured by the barometer. So that, if A is the atmospheric pressure, and B is the pressure of gas in the main, then A plus B is the absolute pressure. There are generally, of necessity, niany points lower than the gasworks, especially in undulating country, but in general, keep low, having regard to otter matters mentioned later with reference to flooding. (c) The character of the surrounding property must be considered. A gasworks is essentially a thing of utility, and can lay little claim to æstheticism ; there-fore the picturesque portions of tlie district should be respected. For the same reason, a site should not be chosen in the fashionable quarter of the town, other-wise complaints from well-to-do residents will be a contimial source of annoyance. Here it may be mentioned that wlien applying for parliamentary sanction to make or purify gas on any land, notices have to be served on all owners, lessees and occupiers of dwelling-houses within 300 yards of any portion of the said land, who may petition the House (before Committee) against the adoption of the site. (d) The ground should be suitable for foundations, botli as to cost and stability. Before a definite agreement is concluded, trial borings should be made, and the nature of the subsoil determined. Hard gravel, ballast and clialk are the ideal. Many clays form excellent foundations, whilst “ made up ” ground (such as disused rubbish heaps, tips, etc.) is probably the most treacherous. Running sand, com-pressible clays, soft peat and fine alluvial soil may turn out to be very untrustworthy and costly. Rock, of course, makes excellent foundations, but is expensive to work, although it may be used for concrete mixing. Fürther economy may be effected by obtaining sand or ballast from the ground. Of extreme importance is the permanent water level, and the possible floods level; both affect the cost of works construction, the former in particular. The latter afEects the actual operation of the works, for no gasworks can be called satis-factory if always liable to floods. The loss of tar and liquor from Underground wells would be considerable and the damage to buildings and plant would be heavy, but the greatest danger would be that of complets stoppage by the extinguishing of furnaces in the retort house. These points are more fully dealt with in Chapter II (Foundations).