LII. ; DISCUSSION. 
strength of steel is about 38,000 or 39,000 ibs. per square inch, 
and the formula for acid steel is— 
38600 + 121 carbon + 89 phos. + R=tensile strength 
For basic steel— 
37430 +95 carbon + 8-5 mang. + 105 phos. + R = tensile strength. 
The carbon manganese and phosphorus are expressed in units 
of 0:001%, and the value of R given in accordance with the 
conditions of rolling and the thickness of the plates or pieces. 
_ The formule were derived from experiments on structural steels 
ranging from 0-02 to 0°35% of carbon, and probably do not apply 
to steels of harder quality or special alloys. 
Mr. H. M. Howe, a high authority on this subject says, “ The 
structure and physical properties appear to depend chiefly—1. On 
the ultimate chemical composition. 2. On the mechanical treat- 
ment it has undergone. 3. On the conditions under which it has 
been heated or cooled, i.e., its “heat treatment” which may 
induce the ultimate components of the mass to regroup themselves 
in new combinations, thus causing one set of minerals to give 
place to another. Just as the character of granite rock may be 
judged from the character of its mineral constituents, as proximate 
chemical compounds, and very imperfectly from ever so exact & 
determination of its ultimate elements, so we must learn to rely 
with less assurance on the ultimate chemical analysis of iron and 
steel, and more on the proximate chemical compounds formed 
therefrom. Unfortunately these latter are difficult of determin- 
ation, or even of identification, and hence we know very little 
about them. It is for this reason that we are as yet unable to 
infer with any great assurance the mechanical properties from the 
chemical analysis.” 
The author considered that the form of the cross section of rails 
was very important, and that the relatively thin flanges adopted 
by English engineers were unsuitable for steel containing a high 
percentage of carbon. The American section appeared to be much 
more satisfactory in every way. 
