PROCEEriNGS OP THE POLYTECHNIC ASSOCIATION. 549 



extreme diameter of the mass in breadth, measured across the large end. 

 The cracks were from a lialf to seven-eigliths of an inch open at the widest 

 part in the center, and passed ofT, at each extremity, to an indefinitely thin 

 wedge. 



45. In no case was there a trace of bad welding or of defective work- 

 manship. They were clean fissures, presenting opposite surfaces of solid, 

 sound metal, though rough by being torn asunder. In this conclusion Mr. 

 Olay coincided. On consideration, it appeared that the phenomenon was 

 simply due to contraction on cooling." 



46. These silent and insidious effects of heat have to do with all our 

 practical pursuits; and nothing in the science of natural philosophy is so 

 little understood, or so necessary to be known, if we would work metals; 

 we can not* ignore them if we would succeed, for they are the principal 

 agents, not only during the fabrication of guns, but the effects must also 

 be considered when we use them. We are not likely to avoid the difficul- 

 ties in our way occurring through their agency in the fabrication of so 

 large a mass of metal by chance; and of course less likely to avoid 

 them also in utilizing the gun after it is made, as a blind man may blun- 

 der into a labyrinth, but he could not be expected to blunder in and out 

 again. 



AMES GUNS. 



4T. Mr. Ames made eight guns before he produced one sound one, and he 

 informed us that he expended §90,000 to produce his first five SO-pounders. 

 This is about the experience of every one making the effort, the cause of 

 which is explained by the failure to comprehend that fissures occur at the 

 time of fabrication from a cause that cannot be averted. I found them in 

 all blocks of twelve inches in diameter and upwards, during my early ef- 

 forts to produce large guns. Upon building up a large mass of forging, 

 the last welds are the largest planes of weakness, (welds of all areas of 

 surface being weaknesses). If all the welds are longitudinal, the fissures 

 will be lengthwise of the block. If transverse, as in the Ames' gun, the 

 fissures are most likely to occur around the bore. If the block is forged 

 hollow, and partially cooled from the interior, the fissures will be in the 

 centre of the mass, equidistant from the cooling surfaces (proportional to 

 the rate in rapidity of cooling.) This statement will be appreciated best 

 by practical founders, who well know that the surface of castings may be 

 sound while the centre is porous. The Dahlgren gun, cast hollow, has its 

 porosity in the center of the block. The Rodman gun, cast hollow, has an 

 annular region of porosity, between the inner and outer surface, always 

 located where the heat leaves the mass last, both in cast and wrought iron. 

 The policy that only attempts to procure guns from those who do not know 

 how to make them, will always result in ruin to the contractor, and disap- 

 pointment to the government. No contractor can long continue to produce 

 guns when receiving less than 625,000 for a lot of five guns that cost $90,- 

 000, as shown by an affidavit of Mr. Ames, and which is according to my 

 experience. 



48. Steamboat shafts, that are only examined on the outside, where they 

 are always dense and perfect, may long continue to be produced and used, 

 made in a faulty and uncertain manner, as all heavy forgiugs are of neces- 



