606 TRANSACTIONS OF SECTION G. 
probably due to the existence in compression, as in tension, of a condition 
immediately after yield in which the stress that the material will sustain is 
less than that required to initiate the yield. 
The effects of eccentricity of loading and initial curvature were investigated, 
and a number of tests of struts of ordinary commercial section compared with 
the theoretical results. 
5. Metals for Structures. By A. T. Waumisuny, M.Inst.C.E. 
Birmingham from an early date has been recognised as one of the chief seats 
of industries in metals, and hence a paper which presents an opportunity to 
elicit a discussion upon some of the latest developments of various alloys used 
as constructive materials appears suitable for a meeting of the Engineering 
Section. Such alloys are not mere mechanical mixtures, but homogeneous com- 
binations, secured by fusion, possessing distinguishing qualities for special 
purposes. 
Copper possesses the element of conductivity. It is always economical to use 
the purest copper obtainable commercially, especially for electrical purposes. 
In contact with iron it is inimical to the iron. Hence roofs are boarded. A 
layer of felt will serve as a separator, care being taken in the attachment of 
bolts to allow no immediate contact between iron and copper. 
Zinc is applied for coverings. Galvanised sheets can be tested with sulphate 
of copper, which will adhere to any exposed surface of the iron not coated with 
zinc. The durability of zinc depends mainly on the spelter from which it is made. 
A covering of zine is better adapted to resist the attacks of a vitiated atmo- 
sphere than galvanised iron, which provides simply an exterior coating. 
Lead has no elasticity, but is useful for girder seatings, where the weight is 
sufficient to crush the lead so as to produce uniformity of pressure upon the 
bearing. It is also serviceable for roof coverings and for flashings. 
Brass, consisting of copper and zinc, is employed for lubricators and pumps, 
while Muntz’s metal—also an alloy of copper and zinc—has superseded copper 
for sheathing vessels. 
Manganese bronze, an alloy of copper and ferro-manganese, is serviceable 
for propeller blades, on account of its toughness; and ordinary bronze—-an alloy 
of copper and tin—is found to possess sufficient fluidity for satisfactory melting, 
combined with slightness of contraction on solidifying. 
Phosphor bronze, by the addition of phosphorus, excels ordinary bronze iu 
hardness, density, and tensile strength, and is used for friction bearings, 
especially when liable to shock; also for sliding surfaces in the case of steel 
shafts, as a steel or wrought-iron shaft would be liable to grip a cast iron bearing. 
Gunmetal, another alloy of copper and tin, takes its name from its employ- 
ment as the metal from which large guns were formerly made, while bell-metal 
and delta-metal also possess characteristics described in the paper. 
When one metal less oxidisable than another comes in contact galvanic action 
may be set up. In the case of mild steel and wrought iron in metallic contact 
the steel may oxidise at the expense of the iron. Iron rivets have been found 
to become slack in steel plates without any special wasting in the steel plates, 
while the iron has wasted somewhat. 
The durability of materials is one of the leading questions of the day. 
TUESDAY, SEPTEMBER 16. 
The following Papers were read :— 
1. Notes on an Engineering Theory of the Gyrostal. 
By J. W. Gorpvon. 
2. Hxposure Tests of Copper, Commercial Aluminium, and Duralumin. 
By Professor Ernest Winson. 
These are a continuation of tests upon the influence of exposure in London 
on the electrical conductivity of light aluminium alloys, reports of which have 
