The exact date of discovery is not known; but early records show it to have been preempted by a Dr Adams in 1812 for the manufacture of saltpetre, and his vats and hoppers are still to be seen.
The coal, previously elevated to hoppers, is dropped into the feeding chambers, which are so arranged that they can travel from end to end of the retorthouse and feed the coal into the retorts.
Guides are placed in front of the retort to direct its course to the coke hoppers or conveyer below, and to prevent scattering of the hot material.
Of the latter there are probably 12,000 to 15,000 species, including 140 butterflies, at least 180 grasshoppers, several hundred bees, &c. The so-called " grass hoppers," true locusts, have done great damage at times in Nebraska.
The material to be melted is introduced into the furnace from the hoppers HH through the charging holes in the roof.