OF GAS EVOLVED AT DIFFERENT PERIODS. 83

culties occur in the practice. The more frequentcharging of the retorts and luting on the covers,*which such a mode of operating require, occasionsa prodigious waste of fuel, time and labour. Agreater number of retorts and more workmen mustlikewise be employed, in order to produce the requi-site quantity of gas daily, wliich the manufactureris called upon to supply ; more space of ground isrequired, and more dead capital must be sunk in theestablishment. The more frequent and suddenalterations of temperature which the retorts neces-sarily suffer, by the more frequent introduction ofcold coal, renders them extremely liable to becomeinjured; and it is almost impossible to maintaina number of retorts thus worked, at an uniformtemperature.

From various statements, which I have beenfavoured with, in confirmation of my own observa-tions on the best method of working - cylindricalretorts, it may suffice to lay before the reader theresult of a series of operations instituted by one ofthe largest and best conducted establishments in

* W hen the cover is ground on, air-tight, the cost of the retort ismuch increased.