L. MECHANICS AND ENGINEERING. 5 41 



methods of manufacturing iron and steel are due to the suc- 

 cessive improvements of Dr. Siemens, Martin, and others. 

 The total annual produce of steel in Great Britain, in 1852, 

 was 50,000 tons ; at present it is over 700,000, and, possibly, 

 nearer 1,000,000 tons. In order to improve the quality of 

 the steel manufactured in Great Britain, Mr. Barlow, j^resi- 

 dent of the Mechanical section of the British Association, has, 

 with others, made a series of experiments for the Institute 

 of Civil Engineers, hoping by these to arrive at some stand- 

 ard of excellence, and some knowledge of the relative merits 

 of different manufacturers, in order eventually to establish 

 rules for the use of steel manufacturers, such as are now en- 

 forced by the Board of Trade government inspecting officers 

 in regard to the manufacture of iron. The experiments made 

 by the committee in question consisted of several series. In 

 the first, twenty-nine bars fifteen feet long were subjected to 

 tension, compression, and torsion, and the principle was es- 

 tablished : 



1. That in steel, as in iron, a bar whose tensile strength 

 is fifty per cent, above that of iron will also exhibit about 

 the same relative increase of strength under the other tests. 



2. That the limit of elasticity in steel is, like that of 

 wrought iron, rather more than half its ultimate resistance. 



3. In reference to toughness and malleability of eighteen 

 samples, each fifty feet long, it was found that w^hen they 

 were subjected to a breaking tension, the elongation at the 

 moment of fracture was, in the most brittle example, 2^ inch- 

 es, but generally varied from 4^ to 9^ inches. In the ex- 

 periments on transverse strain, bars two inches square were 

 bent into a V shape, having an angle of 150 degrees, without 

 any crack. 



In the second series of experiments, a remarkable increase 

 of strength is shown to have been obtained by tempering 

 steel in oil and water, a property that has been for some time 

 made use of in the manufacture of steel guns. 



The third series of experiments was made upon seventeen 

 steel bars, 14 feet long, and 1^ inches in diameter, whose tensile 

 strength varied from 32 to 53 tons per square section ; and 

 upon twenty-four iron bars, whose strength varied from 22 

 to 29 tons per inch. It was shown in these that the extension 

 and compression of steel per ton per inch was little less than 



