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256 pumped through a coil of tubing, and this tubing is heated to an intense heat by the burners, so that almost as soon as the water enters it, it is 'flashed' into steam—that is to say, the process of boiling and steam generation is all gone through in an instant, and the water which enters the coil of tubing at the bottom issues from the top of the coil as high-pressure super-heated steam. This process goes on continually as long as the water is pumped into the coil, as its quantity is always small compared with the length of heated tube.

Figs. 9 and 10 illustrate the Serpollet generator and burner, the latter being dealt with under 'Burners.' The generator

consists of a box with an outer and inner metal skin packed with asbestos to retain heat. Coils of round nickel steel tube are passed through the boiler, and fig. 10 is a plan of one of these coils. The coils are placed one above the other in varying numbers, according to the power of the engine they are required to drive. They are connected to each other by tubes, these junctions being outside the burner space, so that they do not get the direct heat of the fire upon them. It will be understood that these coils are arranged like shelves inside the generator case (fig. 9) in the space, with the