414 



REPORT — 1856. 



From the experimental inquiry into the strength of wrought-iron plates, 

 as applied to ship-building, we have the following results* : — 



Now if we compare the ultimate strength of the Staffordshire plates in 

 the above Table with those since experimented upon, we shall have, taking 

 those in which the strain was applied in the direction of the fibre, for the 

 former 19"563 tons per square inch, and for a mean of nine experiments of 

 the latter, ranging in temperature from zero to 395°, 20*408 tons per square 

 inch. Taking those torn asunder across the fibre, we have for Staffordshire 

 plates in the above Table 21*010, and for those since experimented on 1 9*254 

 tonsf per square inch, which on comparison give the following ratios of re- 

 sults : — 



Staffordshire plates, torn in the direction of the fibre, at a mean tempera- 

 ture of 191°=20*408 tons, and those (in the above Table) at the tempera- 

 ture of the atmosphere, or about 60°=19"563 tons, or in the ratio of 1* : '96 

 nearly, a remarkable coincidence in tensile strength in the two series of 

 experiments. 



Those torn across the fibre, at a mean temperature of 156°, gave a tensile 

 strength =19*254 tons ; those at the temperature of atmosphere 60°, as shown 

 in the previous experiments =21*010 tons, or in the ratio of 1 : 1*091. 



The above results indicate great uniformity in the ultimate strength of 

 Staffordshire plates, which may safely be taken at 20 tons per square inch at 

 all temperatures, between the extremes of zero and 400° Fahr., that is, under 

 a dead weight calculated to destroy the cohesive powers of the material. To 

 what extent these plates would resist impact, at various degrees of tempera- 

 ture, we have yet to determine; but assuming that iron is more liable to frac- 

 ture from an impactive force at a very low temperature ; it will be safer to 

 calculate on a reduction of their resisting powers, at the lower temperatures 

 under 32° Fahr., or the freezing-point of water. 



These experiments might be multiplied to a great extent, in order to de- 

 termine the strength of plates under the varied conditions of temperature in 

 regard to compression, extension, and the force of impact ; but we have 

 already shown in former experiments, and those now recorded above, that 

 iron is not seriously affected by those changes, and we trust the foregoing 

 results will pi*ove sufficient to enable the practical engineer to calculate the 

 resisting powers of iron plates, under all the changes of temperature, from 

 zero up to a red heat. 



* Philosophical Transactions, Part II. 1850, p. 677. 



t The mean temperature of nine, broken in the direction of the fibre, is 191°; and the 

 mean temperature of five, broken across the fibre, excluding red heat, is 156°. 



