Herr Brenner, the engineer of the Erdberg Works, gives a description of how 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 courtyard.  It is a three-lift telescopic one; the lowest lift being 200 feet, the middle lift 197 ft. 6 in., and the top lift 195 ft. in diameter.  The height of each lift is 40 feet.  The several lifts are raised in the usual way; and they all work in a circle of 24 vertical U-shaped channel irons, fixed in the