PART III.

Classification of Pit-coal , and maximum quan-tity of gas , obtainable from different kinds ofCoal .

We have stated already that pitcoal is in thiscountry the cheapest crude natural productionfrom which carburetted hydrogen gas can beobtained in the large way. It is that which yieldsit in abundance, and which. can with the leasttrouble and expence be subjected to the operationit has to undergo for the production of the gas.#[Nature has dealt this mineral out to us, with anunsparing hand, and has provided mines of coalwhich seem to defy the power of man to exhaust.

* Other Substances from which carburetted hydrogen gas, may beeconomically obtained, are animal and vegetable oil, tar, both vegetableand coal tar; pitch, resin, the essential oils obtainable from vege-table and from coal tar, and the compact species of turf. On thissubject we shall speak hereafter