Fig. 32.

seemed to him that no oil-paint could ever fulfil satisfactorily

the requirements of a protective coating for iron or steel

Mr. Young. moisture subsequently deposited upon the structure.

METHOD OF STRENGTHENING GIRDERS OF THE VAUXHALL BIRDGE, GREAT YARMOUTH.

Hence it

structures in England.

What was required was a substance Mr. Young. easily applicable, and chemically unaffected under any conditions

by either moisture, acids, iron-rust, iron, or oxygen. He believed
that the best results were to be
anticipated from the use of one of
the following substances:-

Pure bitumen (dissolved for application in a completely volatile naphtha).

Specially prepared petroleum

tar.

Specially prepared wood-pitch (dissolved in naphtha).

Many difficulties presented themselves. First, practical trials of each substance must be made to discover exactly the necessary consistency to give the requisite elasticity in winter, combined with complete absence of "flow" in summer. Having settled this point, a specification should be framed to ensure the supply of uniform material, and this should be rigidly enforced. A very important point was the proper preparation of the iron surface to receive the protective coating; it was essential to remove every trace of rust, and Mr. Young was confident that it would be economical to spend considerably more time and money over this work than was usually devoted to it. Skilled and well-paid men should do the work, under the close supervision of a foreman known to be conscientious, who had been made to understand the importance of leaving no rust in any corners.

Fig. 32a.

The AUTHOR, in reply, stated that he had tried an air The Author. painting-machine, but the result was not satisfactory. The paint

[THE INST. C.E. VOL. CLXII.]

S

INCHES 12

STRENGTHENING LONGITUDINALS OF BRIDGE BETWEEN ST. IVES AND SOMERSHAM.

S 2

The Author. required to be too liquid, and there was apt to be a serious loss of paint, especially in the case of openwork girders. He does not consider the work was nearly so well done as with a brush. The sand-blast was, however, very useful for cleaning plates, and where air was available it might be used. He found that a few seconds' application gave a bright clean and slightly roughened surface. The apparatus was so simple that it only took a few hours to make, and it might with advantage be often used. He was glad to find that Mr. Barker agreed with his view that rusting should not be allowed to begin, as in his experience it was just the places which had been allowed to rust badly that gave all the trouble.