This is especially necessary in the case of reverberatory furnaces, which are essentially weak structures, and therefore require to be bound together by complicated systems of tie rods and uprights or buck staves.
These uprights are supported on huge piers of masonry and concrete, the foundations for which were carried down, by the aid of iron caissons and compressed air, to a depth of about 15 metres on the side next the Seine, and about 9 metres on the other side.
The shelves should be of slate a, a, supported by iron uprights b, b, each half having a front ledge of bricks set on edge in cement c, c. The slabs of slate forming the shelves should not be too closely fitted, as a small interval will prevent the accumulation of moisture at the bottom of the bed.
This axis is a hollow forging of nickel steel, of which the accurately turned pivots rest on bearings attached to cast-iron uprights bolted upon a massive cast-iron base plate.
The chief portion of this rig is the derrick, Oil which consists of four strong uprights or legs held in Derrick position by ties and braces, and resting on strong wooden sills, which are preferred, as a foundation, to masonry.