60

FORM OF THE RETORTS FOR

retort. If the heat be very intense the whole vesselis rapidly destroyed. If it be too languid, thedistillatory process is protracted, and much fuel,time, and labour wasted to no purpose ; and theretort is speedily deteriorated, if the heat acts uponone part of it more than upon another.

The different kind of retorts of which a descrip-tion has been given in the preceding pages, wereoriginally heated by means of flues passing underand over them. The retorts were placed hori-zontally and fixed in brick-work. One fire-placeat the extremity of the mouth of the retort where thecoals are introduced, and whence the coke iswithdrawn, was allotted to every two retorts in theseries.

At the commencement of the new art of pro-curing light the quantity of fuel as before stated,necessary to decompose a given quantity of coal,amounted to from thirty to thirty-six per cent ofthe coal decomposed ; that is to say, it requiredfrom thirty to thirty-six parts of fuel to decomposeone hundred parts of coal. This quantity hasbeen much lessened by a better mode of settingthe retorts, and it is now the general opinion that