600 



POTASH, PRUSSIATE OF 



tuents hare been found to answer: Ordinary potash, 30 parts ; nitre, 10; acetate of 

 iron, 15 ; charcoal or coke, 45 to 55 ; dried blood, 50. The materials, mixed and dried, 

 are put into retorts similar to those for coal-gas. The animal-matter, however (the 

 blood), is placed in separate compartments of pipes connected with the above retorts. 

 The pipes containing the animal-matter should be brought to a red heat before any 

 fire is placed xinder the retorts. 



In Jig. 1637, ABCD, is a horizontal section of a furnace constructed to receive four 

 elliptical iron pipes. The furnace is arched in the part A B, in order to reverberate 

 the heat, and drive it back on the pipes w, TV', w", ~w'". These pipes are placed on 

 the plane E F, of the ellipsoid, a a, represents the grating or bars of the furnace to ba 

 heated with coal or coke ; n (fig. 1638), is the pot or retort. 



This pot or retort is placed in a separate compartment, as seen in jig. 1638, which 

 is a vertical section, taken through fig. 1640 at the line o, H. x is a connecting tube 

 from the retort and the elliptical pipes w. 



In the section, fig. 1639, the shape of the tube K will be better seen ; also its cocks 

 , and likewise its connection with the pipes w. I, (fig. 1638) is a safety-valve; s, the 



1637 



1638 



cover of the pot or retort ; r, is the ash-pit ; and b, the door of the furnace ; x, is an 

 open space, roofed over, or a kind of shed, close to the furnace, and under it the pipes 

 are emptied ; M, an inclined plane behind the fire-bars. 



The arrows indicate the direction of the current of heat. This current traverses 

 the intervals left between the pipes, and ascends behind them, passing through the 

 aperture.;, 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 of 

 the pot when the valve is. open. Another valve,/, g, must also be open to expose the 

 pot or retort to the direct action of the fire. The smoke escapes by a lateral passage 

 into a chimney, w. 



It must bo remarked that there is a direct communication between the chimney and 

 that compartment of the furnace which contains the pipes, so that the heat, reflected 



