PRUSSIATE OF POTASH.

215

vertical section taken through fig. 121, at the line g, h. k, is a connecting tube fromthe retort and the elliptical pipes w. •

......

J-

mms

In the section, fig. 119, the shape of the tube k, will be better seen; also its cocks «,and likewise its connexion with, the pipes w. Z, is a safety valve; s, the cover ofthe pot or' retort; L, is the ash-pit; and b, the door of the furnace; x, is an openspace, roofed over, or a kind of shed, close to the furnace, and under it the pipes areemptied.

The arrows indicate the direction of the current of heat. This current traversesthe intervals left between the pipes, and ascends behind them, passing through theaperture /, in the brickwork, which is provided with a valve or damper, for closing it,as required. The heat passes through this aperture, and strikes against the sides ofthe pot when the valve is open. Another valve f, g, must also be open to expose thePot or retort to the direct action of the fire. The smoke escapes by a lateral passageinto a chimney n. _

It must be remarked, that there is a direct communication between the chimney andthat compartment of the furnace which contains the pipes, so that the heat, reflectedfrom the part v, strikes on the pot or retort only when the pipes w, w', w", w'", aresufficiently heated.

'In fig. 120 is shown an inclined plane m (also represented in fig, 119) and the junc-tion-tubes which connect the four pipes with their gas-burners z, z, and the cocks m, rri.r , r, are covers, closing the pipes, and having holes formed in them; these, holes areshut by the stoppers e. . .

Whether the pipes are placed in the vertical or horizontal position, it is alwaysProper to be able to change the direction of the current of gas; this is easily done byclosing, during one hour (if the operation is to last two hours) the cocks u, vi , andopening those v! m ; then the gas passes through into the branch K, and enteringv ", passes through q, into w'', through p, into w', and through o, and w, and finally