506 



PARAFFIN 



1604 



we can only state dimensions generally : from 8 to 10 feet is the usual length ; width, 

 from 30 inches to 5 feet 6 inches, commonly 3 to 4 feet ; and height, from 12 to 24 

 inches. The verdict of experience runs in favour of further flattening down to the 12 

 inches. 



Fig. 1603 represents the general arrangement of Mr. Birkbeck's flat D's in plan 

 and section, where a b is the body of the retort, c the outlet-pipe, d e the flat condenser, 

 fff, transverse section of body of retort at/ g', h the retort-door and screw-clamp, and 

 i i i furnace and flue. These retorts are 5 feet 6 inches wide. 



The advantage of such retorts over the D gas-retort is obvious upon consideration 

 of difficulty No. 3. The coal is spread over a larger surface in a thinner layer, and 

 yet a large quantity is included in one charge. All experience goes in favour of spreading 

 out the coal in thin layers rather than packing it in a thick mass. The thinnei 

 the layer the smaller will be the difference of temperature between the retort itseli 

 and the least heated portion of its contents. 



Fig. 1604 represents 

 another form of flat D ; 

 a b, body of the retort ; 

 c d, main condenser and 

 outlets; eee, zigzag supple- 

 mentary condenser made of 

 cast spouting pipe. It is 

 made by Bryan Johnson, 

 of Chester. 



This retort differs but 

 little from the previous 

 one, excepting in having 

 a large outlet with more 

 direct communication with 

 the condenser, and the 

 modified form of the con- 

 denser itself. A large 

 outlet is always advanta- 

 geous, as by its means the 



vapours more readily escape from the decomposing action of the heated retort and its 

 contents. 



Fig. 1605 represents in section the upright retort of Mr. Holmes of Ruabon, where 



1605 



a a a is the body of the retort, b the 

 discharging outlet for the coke, c the 

 charging mouth, d the vapour-outlet, 

 c e and //the condensers. 



In this retort the internal cage shown 

 in the figure serves the purpose of the 

 shelves, &c. already described, as by its 

 means the charge forms a layer occupy- 

 ing the space a a a in contact with the 

 retort-walls, while the vapours pass into 

 the cage and thence to the condenser. 

 It is easily charged where the coal is 

 brought from an upper level. 



Fig. 1606 represents Bryan John- 

 son's modification of the Scotch upright 

 retorts, which work a continuously-de- 

 scending charge. Supposing the retort 

 to be filled, the valve at a is opened, 

 and a portion of the coke let down into 



^____ .__-_^ r _- w __ t ^ le receiving water-tank, c c. The 



hopper, d, being filled with a correspond- 

 ing quantity of fresh cannel or shale, the valve, b, is raised by means of the lever e e, 

 and the retort is filled. This is repeated at short intervals, and thus the charge is 

 gradually worked downwards. Theoretically, these retorts should be hottest at the 

 bottom, and the heat gradually diminish upwards ; but practically there is great diffi- 

 culty in arranging the flues to obtain a regular gradation of heat on account of the 

 rapidity with which the heated gases of the flues ascend when the draught is at all free. 

 In Scotland the common D-shaped gas-retort continues in a few crude works. The 

 retorts in them are now set in benches naked to the fire, and tho waste gas is also led 

 below them ; so that a saving of 4 cwts. of coal in each charge of shale is effected. 

 But, after much controversy, a continuous vertical retort, similar to that in fig. 1606, 



