scribed it at length. A current of steam heated to incandescence, meeting crude petroleum as it drips slowly over cast-iron shelves, takes up all the oil and carries it to a chamber where it meets an air-blast .and passes on to the combustion-chamber. This is a cellular tier of fire-bricks occupying the space over the bridge-wall of an ordinary furnace. Here the combustion begins, and thence the flames pass into the furnace, heating the six piles of iron, of 500 pounds each, which form a charge. Eight tons of boiler-plate can be worked off in ten hours with 300 gallons of crude petroleum, to which should be added 500 pounds of coal for generating and heating the steam. Petroleum is also used as a source of power in hydrocarbon engines (G. B. Brayton's), its vapor being mixed with air and ignited.
Production and Value of Petroleum and its Products.—When the first abundant supplies of petroleum were obtained, the demand for it as an illuminator was small, and it could be bought at the wells for ten cents a barrel, or was even allowed to run to waste (Wrigley), but as the consumption increased the price rose steadily, reaching, in 1864, $13.75 per barrel. The average prices per barrel at Titusville are given below, taken from Stowell's Petroleum Reporter, Pittsburg:
| 1864 | $7 62 | 1870 | $3 74 |
| 1865 | 6 18 | 1871 | 4 50 |
| 1866 | 3 78 | 1872 | 3 84 |
| 1867 | 2 78 | 1873 | 1 84 |
| 1868 | 3 95 | 1874 | 1 29 |
| 1869 | 5 48 | 1875 | 1 48 |
The production of the Pennsylvania oil-region, from 1859 to 1874, according to Wrigley, has been as follows:
| 1859 | 3,900 | barrels | 1867 | 3,347,306 | barrels |
| 1860 | 650,000 | " | 1868 | 3,715,741 | " |
| 1861 | 2,113,600 | " | 1869 | 4,215,000 | " |
| 1862 | 3,056,606 | " | 1870 | 5,659,000 | " |
| 1863 | 2,611,359 | " | 1871 | 5,795,000 | " |
| 1864 | 2,116,182 | " | 1872 | 6,539,103 | " |
| 1865 | 3,497,712 | " | 1873 | 9,879,303 | " |
| 1866 | 3,597,527 | " | 1874 | 10,910,303 | " |
The yield for 1859 is put at about 2,000 barrels by Mr. S. H. Stowell, who has also kindly furnished the following statistics:
Total Yield of the United States in 1875.
| Pennsylvania | 8,787,506 | bbls., of 42 galls. |
| Western Virginia (approximated) | 182,000 | """ |
| All other sources," | 17,150 | """ |
| ———— | ||
| Total | 8,986,656 | """ |
The total value of the crude oils at the wells, up to the end of 1874, is given by Wrigley as $235,475,120, with an additional value for
