of Bronzes from Machu Picchu, Peru. 543 



through the transformation temperature at the rate of several 

 degrees per second. It can he suppressed only by active 

 quenching. 



Before referring to the effect of this transformation on the 

 malleability of these bronzes, it may be well to add that the 

 recent discovery by Hoyt (14) of an additional transformation 

 point in this portion of the diagram has not been disregarded 

 in seeking to interpret the solidificational phenomena. Accord- 

 ing to Hoyt's provisional diagram, we should add to the ten- 

 dencies enumerated above, (3a) for the beta to transform into 

 an eutectoid conglomerate of gamma with little alpha when 

 the temperature has fallen to 590°, (3&) for the gamma to 

 separate alpha as the temperature falls toward 525°, and (3c) 

 for the residual gamma, instead of the residual beta of (4), 

 to develop the final eutectoid of alpha and delta at 525°, 

 instead of at 500°, as previously accepted. All of the num- 

 bered statements are representative of tendencies towards change 

 in the direction of equilibrium. The only one which is dis- 

 tinctly realized under the imposed conditions is that (3c or 4) 

 which results in the complete replacement of an original beta 

 by an eutectoid conglomerate of alpha and delta. Thus, the 

 intermediate changes are not important in this connection. 

 Hoyt's principal findings are (a) that there are two thermal 

 effects below 600° in certain of the copper-rich bronzes and 

 (&) that annealing, or slow cooling, between these two tem- 

 peratures (590° and 525°) develops a new phase, thus far 

 unidentified, between neighboring alpha and beta grains. He 

 considers his results to be of a preliminary nature and only 

 attempts a provisional reconstruction of the diagram. 



Bronzes containing the alpha-phase associated with moderate 

 quantities of the beta phase are malleable and may be worked 

 either hot or cold. This is the condition recognized by Foote 

 and Buell (1. c, p. 539) in their treatment of a cast bronze 

 containing 12 per cent tin. The metal was either forged above 

 the transformation temperature or quenched from such a tem- 

 perature to preserve the beta structure for cold working. By 

 long annealing at a suitable temperature (high enough to pro- 

 mote diffusion and low enough to permit the formation of an 

 alpha solution of high tin concentration — probably 550° is 

 most, suitable) the malleability is still further increased, owing 

 to complete absorption of the secondary constituent with forma- 

 tion of a tin-rich alpha bronze whose properties are independent 

 of the mode of cooling, except that overheating will cause 



