" The effect of arsenic upon steel was quite fully investigated several years ago by Harbord and Tucker. The conclusions given by them may be summarized as follows: -

"Arsenic, in percentages not exceeding 0.17, does not appear to affect the bending properties at ordinary temperatures, but above this percentage cold shortness begins to appear and rapidly increases.

"In amounts not exceeding 0.66 per cent., the tensile strength is raised very considerably. It lowers the elastic limit, and decreases the elongation and reduction of area in a marked degree. It makes the steel harden much more in quenching, and injures its welding power even when only 0.093 per cent. is present.

"These results have been corroborated by J. E. Stead, who found that between 0.10 and 0.15 per cent, of arsenic in structural steel has no material effect upon the mechanical properties; the tenacity is but slightly increased, the elongation and reduction of area apparently unaffected. With 0.20 per cent. of arsenic the difference is noticeable, while with larger amounts the effect is decisive. When 1 per cent. is present, the tenacity is increased, and the elongation and reduction of area both reduced. This increase in strength and diminution in toughness continue as the content of arsenic is raised to 4 per cent., when the elongation and reduction in area become nil"

Influence of Manganese.1 - " In considering the influence of this metal on steel, it must be remembered that, unlike most of the. other constituents, it is not an impurity originally present which the metallurgical treatment has failed to remove, but is, at all events in the case of all steel used for structural purposes, an essential constituent especially added to deoxidise the decarbonized metal so as to prevent its being red short. The effect which manganese has upon the tenacity and ductility varies very considerably with the percentage of carbon in the steel, its influence being much more marked in the case of high than of low carbon steels. In the author's opinion, for mild steel and rail steel, the less manganese a steel contains above that required to insure solid ingots and freedom from red shortness the better, and with reasonable care taken during the manufacture, there should not be the slightest difficulty in obtaining these results with 0.4 to 0.5 per cent. of manganese in the finished product, at all events for mild steel made in the Siemens furnace. ... In the case of mild steel required for boiler plates and for bridges or other structural work, an increase of manganese has a very distinct hardening effect, and above 0.6 per cent. begins to be dangerous, and should not be allowed. The tendency amongst steel makers to bring up the tensile strength to the specification by increasing the manganese, instead of the carbon, is greatly to be deprecated, and notwithstanding the reported excellent records of mild steel plates with 1 per cent. of manganese, and steel rails containing more than this amount, engineers will be well advised to decline to accept such material."

1 F. W. Harbord, " The Metallurgy of Steel," 1904.

It will be evident from a consideration of the foregoing remarks that the relationship between the chemical constitution of mild steel and its ultimate resistance to tension must be of a complex character, and that the attempt to establish a satisfactory formula which shall equate the chemical and physical qualities of any given specimen of the material is surrounded with some difficulties. Several authors have proposed formulae to this end, but it will suffice here to quote some of the conclusions arrived at by Mr. Campbell as the result of elaborate investigations based on a large number of experiments. For the details and methods employed, the reader is referred to the works of that author.1

These conclusions are as follows, converting pounds into tons per square inch: -

1 " The Manufacture and Properties of Structural Steel;" also the paper read before the Iron and Steel Institute at New York, October, 1904.

The strength of pure iron,1 as far as it can be determined from the strength of steel, is about 17.76 to 18.75 tons per square inch.

An increase of '01 per cent, of carbon (determined by combustion) raises the tensile strength of acid steel about 0.44 tons per square inch, and of basic steel about 0 34 tons.

The influence of manganese upon the tensile strength of acid steel is a variable quantity, depending not only upon its own percentage, but upon that of the carbon with which it is associated, and is indicated in the table which follows, for steels of from 0.10 to 0.40 per cent, of carbon.

Table No. 2. Acid Steel

Thus for a steel of 0.35 per cent, carbon and 0.52 manganese, the increase would be 1.50 tons per square inch.

An increase of 0.01 per cent, of phosphorus raises the tensile strength of acid and basic steel about 0 44 tons per square inch.