Modern Gasworks Practice

730 MODERN GASWORKS PRACTICE of less than 300° C. should also be noted; this should be as low as possible, for the reason that a high yielcl of these fracticns indicates a tendency towards undue volatility. More than 10 per cent, remaining at 400° C. would show tlie presence of undesirably heavy constituents ; while the specific gravity of the various fractions should show a fairly uniform progressive rise. Uneven jumps at various temperatures are not a recommendation. A Standard Test The solid residue remaining after the completion of fraotionation is of no little importance, and should never exceed 2 per cent, by weight of the original quantity of oil taken ; in many cases tlie figure will be found to be below 1 per cent. Mexican oil will usually leave a far greater solid residue, occasionally amounting to more than 5 per cent. A standard test for oil which. is carried out at many of the larger gasworks is to distil 10 fluid ounces in a special apparatus, and to carry the temperature up to 350° F., this latter point being gradually arrived at in a period of 40 minutes. The residue remaining behind is bhen cooled, and its specific gravity noted. If the oil is of a desirable quality the gravity will be 0-900. Probably one of the most important items is the sulphur content, and this should not be allowed to exceecl 0-4 to 0-5 per cent. The quantity of water is also to be watched, and may be con-veniently estimated by use of a “ Sutherland bulb.” The rougher test for all oils which lose an inappreciable perceirtage of hydrocarbons on being heated to 110° C. is to weigh 25 grammes in a glass dish, heating to this temperature on a sand bath, and contimially stirring until bubbles of steam cease to form. The sample is then allowed to cool, and is reweighed, when the loss of weight in grammes, miilti-plied by four, represents the perceirtage of water present. Although of considerable importance, owing to its effect on the sulphur im-purities of the gas, the test for sulphur is seldom carried out on gasworks. A con-venient method of obtaining an idea as to the quantity of sulphuretted hydrogen is to hold at intervals a piece of moistened lead acetate paper above the out let of the. condenser ; if sulphiuetted hydrogen is present the paper will be blackened in tlie usual manner, the degree of blackening giving a fair indication of the amount of sulphur in the oil. The total sulphur present can conveniently be arrived at by Carius’s method, or by the use of the bomb calorimeter; but for gasworks purposes a ready means would be that of taking a weighed quantity of oil, mixing it with a spirit (such as alcohol) entirely free from sulphur, and then burning it in a suitable lamp. The products are collected in an apparatus similar to that prescribed by the metropolitan gas referees for testing sulphur compounds. Other iefmements of oil testing include tlie use of the colorimeter and tintometer. But such, apparatus is usually beyond the scope of the average gasworks. ATMOSPHERE IN WATER-GAS PLANTS Somo interesting work in connection with. the effect of atmosphere on the ultimate quality of water gas has been carried out by Downing and Pohlman.1 1 American Gas Inst., 1917.