962 THANSACTIOiXS OF THE AMERICAN IXSTTTUTE. 



water gave a peculiar temper to some kinds of steel. The sword 

 blades of Toledo, no doubt, owe their peculiar temper to the water 

 emplo3Td in hardening them. The manner of dipping diflerent arti- 

 cles must be varied according to their shape. Care should be taken 

 that the water be not intensely cold, for which reason it is best to throw 

 into.it a shovelfull of burning coals, or dip into it a hot iron rod, to 

 take the chill off before dipping the steel. If the article varies in 

 thickness, the thick part should be immersed first, and as near the 

 center of the vessel as can be. In the process of tempering after 

 hardening, xevy little difficulty is found, and it is an easy matter to 

 draw the steel to the required point of hardness. The temperature 

 of boiling water will sensibly soften the temper of steel. The har- 

 dening of steel is the point to which he wished to direct attention, 

 that is, hardening without producing any fractures. A piece of steel 

 thick in one place and thin in another, if hardened, will contract, or 

 it will be warped, but it will not do this if it is allowed to cool 

 equally. Therefore, in hardening the steel must be equally exposed, 

 and also cooled in all the parts. In case the skin left by the hammer 

 is not retained on the steel, it may be coated with some suitable sub- 

 stance, like soft soap, black lead, plumbers' size, c%c. What are the 

 peculiar qualities of different waters, which will best extract the heat 

 from the steel ? Some urge the use of salts and other chemicals that 

 produce an intense cold, but experiments in this direction have not 

 been attended with success. We should approximate the amount of 

 water to the amount of steel. As we usually regard it, water is a 

 non-conductor ; mercury is a better one, and will withdraw the heat 

 much quicker than the water, but, withal, it is not of much value 

 in tempering. Water for large masses of steel is found to be the 

 best, and the great problem is to get the water in such a condition as 

 to take away rapidly the heat, and for this purpose the water should 

 be in close contact to the steel. It is a common thing to see small air 

 bubbles in a tumbler of water after standing some time in a room, 

 and if water is boiled in a flask tliese bubbles will remain ; and if 

 this water is re-boiled it will be found to require more heat to do it, 

 and it must be agitated before it will boil again. It has long been 

 known by smiths that there is no water better for tempering than old 

 water. The cause is simply this : That the constant insertion of red 

 hot metal renders the water airless, and makes it better for tempering. 

 Tlie true system for obtaining a'-suitable water for tempering steel is 

 to get a liquid, the boiling point of which is high. For hardening 



