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March, 1916 flash and setting the stud in place, the link is closed down on the stud and the operation is complete. When the hammer welding process was taken up actively for develop- ment, about one and one-half years ago, the process was essentially what it is today. The chain produced was to all appearances perfectly good, but it failed in tensile test, always falling short of the required ultimate break, and exhibiting a rather coarse granu- lar structure in the fracture. The pos- sibility of the oil fire being the cause was eliminated by the fact that coke fire welds behaved the same way. Alterations to the dies were made but although they were sensible alterations and improvements, the quality of the LARGE STEAM chain did theory that not apply; too. Heat treatment was thought of, but not very seriously at first. There was no equipment for exact methods of heat treatment, nor was there experi- ence for guidance in attacking the problem. But finally, a test triplet of 3-inch chain was one day heated to what looked to be about 2,000 degrees not improve. Even the practice makes perfect did it was thoroughly tested, Fahr. and cooled in air, just as a venture. It tested well above the specified requirements, and then, of course, the solution of the problem was a matter of detail. The completed chain is heat treated in a car bottom fuel oil furnace about ‘od not being THE MARINE REVIEW 6 feet wide and 30 feet long. It is of the overfired type, fitted with 16 burners, eight on each side. When heat treating chain, it is brought up as rapidly as practicable to about 900 degrees Cent., and held at that tem- perature until the charge is ready to come out. The regulation is com- paratively close, the limit of varia- tion being about 15 degrees at any one thermocouple or between couples in different parts of the furnace. There are eight couples in the furnace, four on each side; and the temperature of the. irons is. ‘measured. by, .a..ninth couple, the hot junction of which is inserted in a piece of iron of the same diameter as treatment. the chain under This piece is laid on the car beneath the chain. The couples are of iron and constantan wire. The cold junctions of all couples are led by wires of the same metals to a box in the furnace booth, where the cold junction temperature is measured by thermometer, and allowed for. All temperature measurements are by potentiometer, the galvanometric meth- considered sufficiently accurate. The accuracy aimed at allows a maximum error of 10 degrees Cent., which at 1,000 degrees Cent. is about 1 per cent; but the accuracy actually obtained is somewhat better than that. The action of the heat treatment is to reduce the brittleness, and coarse- ness of grain structure, making the 107 iron ductile enough to yield to shear- ing stresses, yet tough enough to be high in tensile strength. Stiffness must be avoided, as the close-grained, rigid structure desirable in a _ structural forging, does not answer in chain. The distribution of forces in the link is such that in the quarters there are maximums of shearing stress. These shearing stresses build up very rapid- ly, and unless the metal is ductile enough to yield to them, the link will shear off sharply, at a low total longi- tudinal pull, because, of course, iron is much weaker in shear than in ten- sion. Stiffness promotes failure in shear; reasonable ductility combined with reasonable toughness promotes failure in tension. This was the hy- DROP HAMMER AND SINGLE FRAME FORGING HAMMER pothesis first evolved, and experiments warranted considering it a_ theory, especially as more exact methods of heat treatment became available and concordant test results could be ob- tained. It is necessary to explain why the hammer-welded link must have heat treatment, while the hand-welded link does very well without it. The ham- mer-welded link has a long scarf, reaching well around to the quarters. Both in the scarfing and in the, weid- ing operations, the metal is thoroughly hammered; in the latter operation being hammered while cooling from welding temperature down through the critical range. As the scarf is long, this hammering reaches around into