HAMILTON SCIENTIFIC ASSOCIATION 53 



after the annealing temperature has been attained. During 

 the early portion of the anneal the temperature is raised as 

 rapidly as possible without overheating any part of the oven, 

 and when the full annealing heat has been attained the fires 

 are so regulated as to maintain that temperature as uniformly 

 as possible until the end of the firing period. In the majority 

 of foundries the temperature is estimated by observing the 

 color of the ovens, but since the development of Pyrometers, 

 suitable for high temperature measurements, there has been a 

 growing tendency toward their adoption, and the consequent 

 substitution of the more accurate method of regulation for 

 one which depends for its success upon the individual judge- 

 ment of the oven tender (see Plate 2). At the end of the 

 firing period the dampers of the ovens, as well as all other 

 opening, are closed in order to permit of a very gradual cool- 

 ing of the iron. If this is not done and the castings are 

 allowed to be cooled too rapidlj^ they are liable to be 

 rendered hard and brittle with little indication of malleability. 

 When the cooling has proceeded so far that the ovens are 

 black hot, the doors are opened and the contents removed as 

 required. 



The actual temperature which has been found most suit- 

 able for the anneal is from 1,500° to 1,600° Fahrenheit, 

 although the necessary changes in the white iron begin at 

 about 1,250° Fahrenheit. The temperature conditions of the 

 process may be represented b}' a curve showing the sharp 

 rise at the beginning to about 1,500°, a fairly uniform portion 

 between 1,500° and 1,600°, and a gradual decline to 500° or 

 600°. 



Turning our attention to the condition of the metal after 

 the anneal, we find that it has undergone a most remarkable 

 transformation. The brittleness of the white iron has been 

 exchanged for a remarkable softness and malleability, the 

 fracture has become black and the crystalline appearance has 

 been lost. These changes are due to, or all events are 

 accompanied by a transformation in the condition of the 

 carbon. In the white iron it has been pointed out that the 



