In the Pan process, several pans, having a width of 20 to 24 ft., a length of 100 ft. in two sections, and a depth of 12 in., are placed under one roof. Adjoining this front row of pans at the back are arranged a second row of pans, 20 to 24 ft. wide, 30 ft. long, and 12 in. deep, set from 12 to 16 in. higher than the front pans, to enable the easy transfer of brine by syphon from the back to the front pan. The grates are 3 to 4 ft. wide, by 5 to 6 ft. long, and the pan bottoms, which are directly over the fires are protected from a too intense heat by fire-brick arches, which decrease in width from the front to the back of the pan, while the air spaces between the arches increase in width in the same direction. Beyond 20 ft. from the front of the first section of the pan they cease altogether. To convey the heat as close to the pan bottom as possible, beyond the last arch, the flues are usually filled in with earth or plaster, and thus the distance between the pan and flue bottom is between 3 and 4 ft., or even less, at the end of the first pan, where a perpendicular wall, called a bridge wall, reduces the space to about 1½ to 2 ft., through which the products of combustion pass under the back pan and finally into a common chimney. After the pans are properly cleansed they are white-washed with a thin milk of lime to prevent their rusting before they become thoroughly heated; the fires are started, and the pans are filled by syphons to a depth of about 6 in. with brine from the back pans. The former are so inserted that a constant flow of brine passes from the back pans into the last section of the front pans, and from these under the partition into the first section. Into the back pan flows a constant stream from the outside cistern, until the front pans are sufficiently full, when the flow is stopped. After a sufficient amount of salt has collected in the first section of the front pan it is removed to the “drip” for drainage. This is called drawing or raking the pans. The front pans are refilled from the back pan in which the brine has become considerably heated, and thus is prevented a too rapid cooling of the brine in the front pan, which would seriously interfere with the formation of a properly grained salt. For the same reason, the partition is placed in the front pan, since it prevents any cold brine from coming suddenly into the first section, but is compelled to enter at the bottom of the pan, where the temperature is at the highest. For the purpose of aiding the formation of fine grained salt, butter, specially prepared soft soap, gelatine, or white glue are added, and when this variety of salt is made the pans are drawn every 45 to 60 minutes. In the manufacture of coarser grained salt, the drawing of the pans take place at intervals of from two to twelve hours, while the temperature is reduced from 229° F. to as low as 148° F., according to the size of the grain.