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shale with the cannel, which is especially necessary when cannel slack, for which 

 these retorts are best adapted, is used. Where the material to be used is liable to 



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soften and become at all adhesive when treated, these retorts are utterly useless. 

 When it forms a hard clinker coke, they may with careful management be advan- 

 tageously used, as the quantity of work done by them is very great. 



Another difficulty is presented by a very friable material which readily crumbles 

 into dust, as such dust flies over with the vapour and makes a very dirty oil. 



Among the earlier efforts to improve the process of distillation of coal, &c., was 

 the application of superheated steam. Several patents have been secured for this, the 

 general object being to drive the heated vapour through a mass of coal broken into 

 small pieces, and thereby apply the heat directly to each fragment, thus completely 

 avoiding the third source of excessive temperature, besides affording an effectual 

 means of regulating the temperature while diffusing it equally throughout the whole- 

 mass. 



This method, though so admirable in theory, has failed in practice, after being well 

 tried by Messrs. Young, by Messrs. Lavender and Co. at the Canneline Oil Works, 

 Flintshire, and by others. It is now, as far as we are aware, altogether abandoned. 

 The difficulties that have led to its abandonment were mainly the costliness of the 

 superheating process, and the great amount of steam required to be formed in the 

 first place, and then to be condensed. It must be remembered that while the latent 

 heat of steam is equal to about 1000 Fahr., that of the hydrocarbons primarily to be 

 distilled is not above one-tenth of this ; thus every pound of steam requires for its 

 condensation about ten times the amount of cooling surface which is necessary for 

 the condensation of a pound of oil-vapour ; and the complete condensation of the 

 steam is necessary, as it obstinately retains an important quantity of oil-vapour 

 diffused through it. 



The use of heated gases, such as nitrogen, carbonic acid, &c., in the place of 

 steam, overcomes this difficulty ; but the cost of preparing the gases renders their 

 application equally impracticable on the primary score of economy. 



The ' meerschaum retort ' is a modification of the principle of distilling the coal by 

 internal application of heat. This is effected by means of . large chamber or kiln, 

 rather than retort, constructed of fire-brick and shaped like a huge tobacco pipe- 

 bowl, with which an exhaust-pipe like the stem of a tobacco-pipe communicates 

 with the bottom. This exhaust-pipe communicates with suitable condensing 



