PART V.

Di fference in the quantity of Gas evolved duringdifferent periods of the distillatory process ,and economical considerations resulting there-from in the manufacture of Coal Gas .

In conducting the decomposition of coal, theevolution of the gas is far from being, with regardto quantity, uniform during different periods ofthe distillatory process. The formation of the gasis more rapid in the beginning of the process, andgradually slackens as the operation proceeds. Thegas also differs in its chemical constitution,at different periods of the process; althoughin the case of large supplies, this difference is oflittle consequence after the gas is purified in the