and the other articles produced by the destructive distillation of wood, such as charcoal, tar, acids, w ood naphtha, etc., will more than pay all expens e s and bring the i l luminating gas down ...

When wood is subjected to destructive distillation or is greatly heated in close vessels, an acid liquor oozes over with the tar and gaseous products. This acid liquor is the pyroligneous acid.