96

TEMPERATCUE FOR

elsewhere in this country, and where saving of timeis also an object of primary importance, it is clearlyestablished, that the manufacturer who pursues themethod of decomposing- coal in masses from five toeight inches and upwards in thickness, by meansof cast-iron retorts,* w ill consult his interest best,by employing such a high temperature for thedecomposition of the coal, as will produce in theshortest time the greatest possible quantity of gas,from a given quantity of coal, without regardingthe unavoidable deterioration of the retorts. Butin places where coal and labour is cheap, it w ill behis interest to save the retorts at the expence ofthe coal. But that this fact may not rest onmere general assertion, I shall subjoin for thesatisfaction of the reader a few statements of ex-periments made upon a large scale for the pur-pose of ascertaining these facts.

* The Retorts should be manufactured of what is called in com-merce, iron of the second process. The best cast-iron of this kind, isof a light grey colour, its fracture is granulated and dull, it receives adent from the blow of a hammer. The cast-iron which exhibits a darkgrey or black colour inclining to blue, and presents granular concre-tions, readily friable, and therefore unfit for vessels intended to standa long continued heat.