TENSILE STRENGTH OF BOILER PLATE. 406 



On the Tensile Strength of Wrought Iron at various Temperatures. 

 By William Fairbairn, F.R.S. ^c. 



On a previous occasion I had the honour of conducting, for the Association, 

 a series of experiments to determine the effects of temperature on the 

 strength of cast iron. In that inquiry I endeavoured to show to what extent 

 the cohesion of that material was affected by change of temperature, and 

 taking into account the rapidity with which iron imbibes caloric, and the 

 facility with which it parts with it, it is equally interesting to know to what 

 extent wrought iron is improved or deteriorated by similar changes. In the 

 present inquiry, as in the former on cast iron, the expansion of the metal 

 by heat is not the question for solution. Rondelet, Smeaton and others have 

 already investigated that subject, and it now only remains for us to deter- 

 mine the effects produced on the strength of malleable iron by changes of 

 temperature, varying from — 30° of Fahrenheit to a red heat, perceptible in 

 daylight. 



The immense number of purposes to which iron is applied, and the changes 

 of temperature to which it is exposed, render the present inquiry not only 

 interesting, but absolutely essential to a knowledge of its security under the 

 varied influences of those changes ; and when it is known that most of our 

 iron constructions are exposed to a range of temperature varying from the 

 extreme cold of winter to the intense heat of summer, it is assuredly desirable 

 to ascertain the effects produced by these causes on a material from which 

 we derive so many advantages, and on the security of which the safety of 

 the public not unfrequently depends. 



Independent of atmospheric influences, another consideration presents 

 itself in reference to the durability and ultimate stability of iron under 

 changes much greater than those alluded to above, and this is the strength 

 of such vessels as pans and boilers subjected to the extreme temperatures of 

 boiling liquids on one side, and the intense heat of a furnace on the other. 

 But even these extremes, however great, do not seem seriously to affect the 

 cohesive strength of wrought-iron plates, nor do they appear to cause any 

 disruption of the laminated structure which results from the system of piling 

 and rolling adopted in the manufacture, excepting only where small particles 

 of scoria happen to intervene between the laminated surfaces. These not 

 unfrequently prevent a perfect welding, as the plate is compressed by 

 passing through the rolls, and the effects of temperature are strikingly 

 exhibited in the production of large blisters upon the surface of the plate, as 

 shown in the annexed sketch at 



a, a. Now the reason of this is Fig. I. 



the want of solidity and homo- 

 geneity in the plate, and the con- 

 sequent expansion of the lower 



part exposed to the greatest heat. Let us suppose, for the sake of illustra- 

 tion, the plate to be f ths of an inch thick, and the surface b to be the inte- 

 rior of a boiler-plate, and the surface a, a to be exposed to the action of the 

 fire in the furnace. In this case it is evident that the temperature of the side 

 a, a may be upwards of 1000°, while that of b is very little above 212°, or 

 the temperature of boiling water ; and supposing there be any imperfection or 

 want of soundness in the plate, the result will he a greater expansion on the 

 exterior surface, causing it to rise up in blisters in the manner we have de- 



