TREATMENT OF MANUFACTURED IRON AND STEEL. 265 
Steel has the advantage of possessing the same tensile strength 
and elongation with and across the’ length of the plates, and it 
will be readily understood that this is especially valuable in many 
cases of constructional work. 
6 
It is of the greatest importance that material of a ductile and 
reliable character, such as mild steel, should be used in the manu- 
facture of bridges &c., because no matter how carefully the design 
may be prepared, some unforeseen events may arise, such as a 
slight movement in the foundations &c., that will throw greater 
stresses than were anticipated upon some member of the structure. 
As an instance of this, the author has known of cases in Australia 
where the outside tension members in the bottom boom of a truss 
girder, have had to be protected from the sun’s rays, by boarding; 
as they became bent owing to their expansion by heat, and stresses 
they were designed to carry, were thrown upon the adjacent and 
similar members. 
There are two descriptions of steel largely manufactured for 
constructional purposes; one generally termed the ‘‘ Siemens 
Martin,” and the other known as the ‘“ Open Hearth Basic.” The 
former is made by the open hearth process from high-class hematite 
iron practically free from phosphorous ; and the latter by the same 
process from iron possessing an amount of that element which 
would produce cold shortness in the finished material if it were 
not eliminated in the furnaces during the process of manufacture. 
The former, or as it is frequently termed, open hearth steel made 
by the “Acid Process” is in the best practice, specified for boiler 
plates where steel is used, and steel produced by both methods 
is employed for bridges and works of that character. 
TESTs. 
The following are the tests usually required by some of the best 
known British engineers, for iron and steel for bridges, and steel 
for boilers. 
