404 MEMOIR OF DAXIEL TREAD WELL. 



improved cannon, tlio processes of manufacture, and the efforts he made to bring it to 

 the favorable notice of the government, 



" Having been engaged more than four years in inventing and reducing to practice a 

 method of making cannon of wrought iron and steel, which have been proved, by the most 

 severe tests, greatly superior to cannon made of bronze or cast iron, I have thouglit that 

 a general account of my mode of operation, and of tlic principles and laws upon which it is 

 founded, may not be without interest to engineers. 



" The first cannon made after the invention of gunpowder were of wrought iron. They were 

 commonly formed of staves and hoops united together by brazing. Those engines, it seems, 

 answered for throwing light projectiles, as stone balls, the powder probably being much in- 

 ferior to that now used with artillery. It is certain, however, that none of the old wrought- 

 iron cannon made in this way would withstand a single discharge if loaded with modern powder 

 and solid iron shot. The early abandonment of these guns, and the substitution of those made 

 of In-onze and cast iron in their place, does not prove, however, that the material was inferior 

 to bronze or cast iron, as it is evident that this mode of construction must, in itself, be essen- 

 tially defective. No fact in the arts seems to be more confidently relied upon, than that 

 wrought iron is much stronger than cast iron or bronze, and this is certainly true if we expose 

 the wrought iron to the testing force in one particular direction only. But all wrought iron is 

 in its structure fibrous, the fibres being more or less distinctly marked, according to the 

 process followed in the manufacture of the iron. In wire it is most clearly apparent, the 

 fibres, in some cases, being so easily parted tliat the wire can be split with a knife. In sheets, 

 formed by the rolling-mill, the fibres are arranged in plates or lamina, and tlicse often so 

 slightly adhere one to another that they may be separated like the layers of a pasteboard. With 

 hammered iron, tlie grain or fibres are less apparent, and the bars possess, in tlieir different 

 directions, greater equality of strength. By comparing the various operations of wire-drawing, 

 rolling, and hammering, we are led to the conclusion that the fibres are always formed in the 

 direction in wliich the iron is extended, and tlie cohesion is least amongst the atoms which 

 are spread over each otlier. All that is here said of iron is equally true of steel, the cohesive 

 force of which, however, exceeds in an essential degree that of iron. Cast iron and bronze, on 

 the contrary, are of equal strength in all directions ; their structure appearing as an aggre- 

 gation of grains, assuming the form of crystals, often apparent to the naked eye. 



"The strength or direct tenacity of these various metals, the wrought iron and steel being 

 tested in the direction of their fibres, may be taken as follows for each square inch area of the 

 metal : — 



Step] (English spring) 100,000 pounds. 



Wrought iron 65,000 " 



Bronze 30000 " 



Cast iron 25,000 » 



That is, a bar of steel of one inch square will raise and sustain a wcigiit of 100,000 pounds, and 

 bars of wrought iron, bronze, and cast iron, of 65,000, 30,000, and 25,000 pounds, respectively. 

 This statement, supposing all the materials of good quality, is a near approximation to the 

 truth, as derived from the best experiments. If, however, the steel or wrought iron be exposed 

 to the testing force in such a way that the fibres shall be separated laterally instead of being 

 broken, the strength will rarely be found to exceed that of bronze or cast iron even. 



