PARAFFIN 



507 



but of a more oval shape is preferred. The merits of the case appear to be that 

 parties desirous of making only crude oil should erect horizontal retorts, whilst refiners 

 making their own crude should rely on verticals. The oil from vertical retorts has a 



1606 



specific gravity of 890 ; that from horizontal retorts varies from 850 to 860 ; but 

 indeed has been as low as 840. The latter commands the best price in the market ; 

 but the former is more cheaply made by the refiner ; and it is more valuable, for 

 though there is less burning-oil and naphtha, it contains 3 per cent, more paraffin. In 

 the Scotch upright retort the distillation is per ascensum^, and the condensers are 

 simpler than those figured in the drawing ; indeed, very complex forms of condensers 

 were used in the first stages of coal-oil making ; such as worm-tubes, with water-tanks 

 and hydraulic mains of various patterns. 16 is now found that simple radiation is 

 a sufficient cooling agont. 



Mr. Young of Straiton, near Edinburgh, some years ago introduced a very effective 

 retort resembling somewhat in section fig. 1605. But the cage is represented by 

 a framework of impervious iron, round which the waste gases are first conducted away 

 with the other products in this case by distillation per descensum, but afterwards 

 reintroduced by a suitable opening play, assisting the small fire. Not only is coal 

 saved, an item of importance even in days of cheap fuel, because such shale works are 

 generally far from coal-pits, but more paraffin is obtained. The Oakbank Oil Com- 

 pany, Midcalder, have used these retorts with great satisfaction. 



The revolving retort is an American invention. It is shown in elevation and 

 section in figs. 1607, 1608, 1609, the lettering being the same in the sections and the 

 elevation. 



a a is the body of the retort, a cast-iron cylinder (wrought-iron has also been 

 used) usually about 7 feet diameter and 7 feet long. The cylinder turns on the 

 axles c and d d ; the latter, d d, is hollow and serves also as the vapour-outlet to the 

 condenser g, which has a second or supplementary condenser shown in section at h, 

 connected with the first by the swan-neck i i (fig. 1608). 



The cylinder or body of the retort is turned very slowly by means of an endless 

 screw, e, working in a toothed-wheel, / /. The charging door, k, is on the opposite 

 face of the cylinder. The heat is communicated from the furnace by means of an 

 arched flue which embraces the whole of the cylinder. To charge the retort the 

 door, k, is turned upwards, as shown in the figure ; to discharge, it is by a half-revolu- 

 tion from this position brought to the lower side. 



The action of these retorts will be easily understood. The charge is continually 

 rolled over, and thus fresh portions are brought in direct contact with the heated 

 surface. By this means a very rapid distillation is effected. In this respect they are 

 most efficient. The objections to them are their costliness in the first place, and their 

 liability to crack, from the unequal expansion of so largo a surface of metal. They 

 cannot be protected all round, as ordinary retorts are, by a casing of fire-bricks, and 

 being thus exposed to the direct action of the fire are rapidly destroyed, especially if 

 great caro is not taken to remove the lining of carbon-deposit which forms on the 

 inside. When ordinary cannel is used, they have to be cleaned out weekly, which 

 involves a serious loss of time in cooling down and reheating all the surrounding 

 brickwork. This difficulty is to a great extent overcome by working lumps of hard 



