168 PROPERTIES OF IRON AND STEEL CONSTRUCTIONS. 



Steel, with increasing mixture of phosphorus, loses its capacity to undergo 

 repeated heating without losing its peculiar properties. 



In the year 1871, Joule, Fairbairn, Spence and Brockbank contributed 

 to the Manchester Literary and Scientific Society four papers upon the in- 

 fluence of cold upon iron and steel. All agreed that resistance to dead load 

 was not diminished by cold, but considerably increased. Brockbank held 

 it certain that cold diminishes resistance to shock; this, Joule and Fairbairn 

 did not admit. All referred to experiments. No one will question the ex- 

 actness of Joule's tests; but the test-pieces were wires, needles and nails, so 

 that the results may not hold for larger pieces; while Fairbairn and Spence 

 tested only under dead load. A series of observations by Brockbank eon- 

 firm the results obtained by Sandberg. Eails were tested with blows; and 

 in frosty weather they had far less strength than at ordinary temperature: 

 a hollow cast-iron core-rod, about which a cylinder had been cast, cooled 

 down to — 7^°, broke square and smooth, leaving a brittle-looking surface, 

 while the pieces were made stiff and sound again by heating. A rod of 

 round iron of best quality, of 38 mm. diameter, which lay a week exposed 

 to frost and was covered with ice, broke at 4^° under a single blow of a 

 hammer weighing 5.4 kil. 



All authorities admit the increase of resistance to tension under great 

 cold, though they deny that there is a diminution of power to resist shocks. 

 This is bad reasoning. It is certain that resistance to dead load is some- 

 what increased by frost; and besides this, according to StyflPe, the elastic 

 limit; just as is the case under hammering, rolling, hardening, etc.; but as 

 with all the latter, resistance to shock increases, there seems to be bo reason 

 for a contrary judgment in the first case. Styffe has proved that iron be- 

 comes stiffer with decrease of temperature'; agreeing with Sandberg. 



Thurston concludes from results of hie experiments that phosphorus and 

 other substances, inducing cold brittleness, may impair resistance to shock 

 at low temperatures, which seldom occur; and that in other cases resistance 

 to dead load, as well as to shock, is increased by cold. This would be novel, 

 but it must first be proven. Thurston's test-machine is well adapted to the 

 lecture-room, being convenient and cheap ; but it is not suitable for scien- 

 tific experiments requiring results numerically exact. The velocity, an 

 important element, is not regulated ; the methods of measurement are much 

 too primitive to answer to small differences due to temperature; and it is 

 not to be taken for granted that torsion-tests are best suited to determine 

 the properties ot resistance of fibrous and laminated metals. 



In a report of the Massachusetts Eailroad Commissioners (1874) men- 

 tioned by Thurston, it is said, that " cold does not make iron and steel brit- 

 tle and unsuitable for mechanical purposes, and that it is not the invariable 

 rule that the most breakings occur on the coldest days." The membership 

 of the CommiBsion is not given, nor is it certain what kinds of metal were 

 under consideration. Did it contain a large percentage of phosphorus? 

 Were the rails iron or steel? It has been found in Northern climates 



