the hot fuel it is reduced to carbonic oxide. The liberated oxygen combines again, partly with some of the carbonic oxide, to become carbonic acid, and partly with carbon to form carbonic oxide. The gas used in the internal combustion engine should be clean and free from sulphur compounds, and it must be cooled to give a large amount of energy per unit volume in the cylinder. Hence, for such purposes, it is best to use anthracite coal, which, being nearly pure, does not contain sulphur nor yield much ammonia, tar, or other products which readily condense and foul the pipes and valves. Good anthracite is also suitable fuel for the generator, because it makes a dense fire, free from holes or passages, and it does not cake or yield much clinker. Ordinary gas coke in small pieces free from sulphur, which does not yield large quantities of clinker and which has been subjected to high temperatures in the retorts, is also used with good results. The gas is cooled by passing through the pipes F, then cleansed by passing through water in the hydraulic box H, then through the sawdust scrubber J on its way to the coke scrubber K inside the gas holder. The automatic regulator O regulates the supply of steam to the generator and, within certain limits, governs the production of gas, by the rise or fall of the gas holder, and this not only avoids waste of fuel, but renders the storage of much gas unnecessary, as the production of gas is very rapid. Carbonic oxide is a very poisonous gas, and devoid of colour, whilst having great heating power; but Dowson gas has a characteristic though very slight smell, not readily detected, but, with the proper precautions of sound fittings the risk is reduced to a minimum. Unfortunately for Mr. Dowson, gas engine makers have not paid sufficient attention to the construction of engines to deal with producer gas to the best advantage. It is beyond dispute that good results are obtained from producer gas, even when using coke. The cost of maintenance of a boiler has long been known and accepted as inevitable. We may also accept the cost of a gas-producer plant, for a gas engine, though the up-keep will be less. About four times the amount of Dowson gas is required than lighting gas in each charge which enters the cylinder of the gas engine. A safe rule for the size of gas supply pipe is one third of a square inch for each indicated H.P. when working under ordinary conditions. The ordinary method of mixing gas and air gives the best results with producer gas, though necessitating a specially constructed channel. The difficulty with producer gas is to get enough into the cylinder, with the required volume of air; as the port in the cylinder is open for the same time as for town gas, it is important that the gas passages should be as free as possible, and that the valve should admit fully the extra quantity of gas. To ensure good working more 'lead' is necessary with Dowson than with coal gas. The usual practice of regulating the air inlet near the combustion chamber does not give the best results, which the author has obtained by throttling the air at the extreme end of the air pipe and depending on the momentum generated in the column of air contained in the length of pipe when the piston is at its maximum velocity. By this method the gas is allowed to enter the combustion chamber freely and thoroughly mingle with whatever burned gases the cylinder may contain; when, towards the end of the charging stroke, the piston speed lessens, there is considerable commotion in the air pipe, which assists the incoming gas thoroughly mingling with it. With an engine having a cylinder 19 × 30 inches stroke the author has found that the valves require cleaning, &c., as follows: Exhaust valve required cleaning and grinding in every six weeks. Air valve required cleaning and grinding in every six months. Gas valve required cleaning and grinding in every two weeks. This engine runs about 56 hours per week, and develops about 80 per cent. of its maximum power. CHAPTER XXXIV MANSFIELD OIL GAS MESSRS. Mansfield & Sons are makers and patentees of plants for making cheap gas from oil, sawdust, nut shells, mineral, vegetable, and animal matter. The Mansfield oil gas apparatus is shown at fig. 193. The producer or gas generator has a strong cast-iron casing D, lined inside with moulded fire clay blocks. The cast-iron retort C hangs by a flange on the fire clay cover, and can be lifted out or replaced in a few minutes. The retort is heated and kept up to the desired temperature, from 1,600° to 1,800° F., a bright cherry red, by a fire of coal, coke, wood, or other fuel, placed on bars at L and regulated to a nicety by the sliding grids M, the colour of the retort being observed through · a sight hole. These retorts usually last two years with moderate use, and the clay blocks last for some two or three years. The trouble of screwing up and making joints in the ordinary way is obviated by the simple expedient of a socket in top of the retort, filled with melted lead, and a socket on top of the standpipe at N, kept filled with water. These are arranged to prevent the escape of gas, acting at the same time as safety valves, because, whenever any extraordinary back pressure occurs, the gas forces its way out at N or J. The lower end R of the standpipe dips into water in the hydraulic box G, which is regulated by the half-inch siphon bend J. Any accumulation of tar can be cleared out occasionally at the door K. To make gas, the usual procedure is to light the fire below the retort and keep up a regular heat until the lead in the ring space C on the top of the retort is all melted, a sign that a sufficiently high temperature has been attained for the manufacture of the gas. The can or cistern A is filled with oil or melted fat, which trickles into the funnel and through the half-inch siphon pipe B in a thin, continuous stream, one-sixteenth of an inch thick, into the upper part of the retort. The oil is vaporised in this pipe, and the oil vapour, passing down the interior into contact |