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252 and when the burner is applied to a flash boiler, a regulator is employed, which is called the thermo regulator, by which the supply of vapour to the burner is automatically controlled by the temperature of the superheated steam. For explanations of 'Flash boiler' and 'Superheat,' see 'Boilers.'

The Syndicate vaporiser is an arrangement which permits paraffin to be burned in petrol burners of the Locomobile type. It consists of a vaporising coil heated by a suitable wick lamp, and to ensure a sufficient supply of air being mixed with the vapour a small jet of steam blows into the burner from the boiler by the side of the vapour nozzle, and so sucks sufficient air into a type of burner which would not otherwise supply enough for satisfactorily burning paraffin vapour. The arrangement was described and illustrated in 'The Autocar,' of January 18th, 1902.

The Serpollet burner shown in fig. 9 has a number of small atmospheric burners, and the paraffin is vaporised by being pumped in a tube across the fire-box before entering the burners. The initial heat is obtained by a gas-flame, or by burning alcohol in a tray under the vaporising tube. The burners are concentric; the vapour passes up a central tube surrounded by two air-tubes, and the suction of the vapour draws air up these, and it mixes with this air before burning.

The Boiler.—We have seen how the mission of the burner is to supply heat to the boiler, and how that heat is generated and controlled; the next step is to consider the generation of steam in the boiler. The duty of the boiler is to supply high-pressure steam to the engine. Steam is the gas which water gives off at boiling point, 212° Fahr. High-pressure steam is steam which is confined in a space smaller than that which it would occupy at atmospheric pressure. The smaller the space in proportion to the volume of steam, the greater the pressure. Steam so confined has immense elastic and expansive force, and the boiler and burner are so proportioned that when the pressure of steam is once obtained, the continual generation of it is so