the roof of a house, 54.6 meters wide, for a gasholder in Berlin, was
raised to a height of 22 meters. In that instance the iron structure was
put together at the bottom of the tank, leaving the rafter ends and the
mural ring. The hoisting itself was effected by means of levers--one to
each rafter--connected with the ironwork below by means of iron chains. At
the top there were apertures at distances of about 26 mm. from each other,
and through these the hoisting was proceeded with. With every lift, the
iron structure was raised a distance of 26 mm.

[Illustration: FIG. 2.]

Herr Brenner had considerable hesitation in raising in the same way the
structure at Erdberg, which was much larger and heavier than that in
Berlin. The simultaneous elevation to 48 meters above the level, proposed
to be effected at forty different points, did not appear to him to offer
sufficient security. He therefore proposed to put the roof together on the
ground, and to raise it simultaneously with the building of the wall;
stating that this mode would be perfectly safe, and would not involve any
additional cost. The suggestion was adopted, and it was found to possess,
in addition, the important advantage that the structure could be made to
rest on the masonry at any moment; whereas this had been impossible in the
case at the Berlin Gasworks.

[Illustration: FIG. 3.]

HOISTING.

At a given signal from the foreman, two operatives, stationed at each of
the forty lifting points, with crowbars inserted in the holes provided for
the purpose, give the screws a simultaneous turn in the same direction. The
bars are then inserted in another hole higher up. The hoisting screws are
connected with the structure of the roof, and rise therewith. All that is
requisite for the hoisting from the next cross beam is to give a forward
turn to the screws. When the workmen had become accustomed to their task,
the hoisting to a distance of 1 meter occupied only about half to
three-quarters of an hour. At the outset, and merely by way of a trial, the
roof was lifted to a height of fully 2 meters, and left for some time
suspended in the air. The eighty men engaged in the operation carry on the
work with great regularity and steadiness, obeying the signal of the
foreman as soon as it was given.

THE GASHOLDER.

The holder, which was supplied by the well-known firm of Messrs. C. and W.
Walker, of Finsbury Circus, London, and Donnington, Salop, was in an outer