The annular space between the two vessels is filled with water to the same level as the solution in the receiver, and the latter is provided with suitable pipes or coils, in which steam is caused to circulate for the purpose of raising the solution of the desired temperature, and effecting the digesting process. At the same time any steam generated collects in the upper part of the boiler, and maintains an equal pressure within the whole apparatus. The arrangement is shown clearly. Within the boiler is placed the receiver, of pottery, lead, or other material, leaving an annular space between it and the boiler; this space is filled with water. The receiver is furnished with a series of pipes, in which steam or hot water circulates, to heat the charge to the desired temperature. These pipes may be arranged either in coils or vertically. The latter are provided with inner return pipes, so that any condensed water accumulating at the bottom may be forced up the inner pipes by the steam pressure and escape at the top.

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MPAA: G
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