Foots and Buell — Peruvian Bronze Axes. 



129 



No. 1 



Tin 12-03 



Copper 88-06 



Iron 008 



Silver none 



Sulphur 0-35 



Lead none 



No. 



No. 3 



100-52 



5-58 



3-36 



93-94 



96-44 



none 



trace 



0-65 



none 



0-08 



0-23 



trace 



none 



100-25 



100-03 



The results show that the alloys are all bronzes which vary 

 considerably in their percentage of tin and contain a small 

 amount of sulphur. No. 2 also contains silver in small amount. 



The alloys of copper and tin have been most thoroughly inves- 

 tigated by Heycock and Neville*and by Shepherd and Brough.f 

 Their results show that alloys containing not more than approx- 

 imately 10 per cent of tin consist entirely of a solid solution of 

 tin in copper, stable at all temperatures below the melting 

 point, and made up of so-called a-crystals. Alloys containing 

 between 10 and 22 per cent of tin deposit on solidifying a 

 mixture of a- and /3-crystals. The /3-crystals consist also of a 

 solid solution of the two metals but contain more tin than the 

 a modification. They are stable only above 480° C. and if 

 cooled slowly below this transition temperature, S-crystals are 

 formed. These are extremely brittle and an alloy containing 

 them cannot be successfully worked either hot or cold. If, 

 however, the alloy is quenched rapidly from a temperature 

 above 480° C, a mixture of a- and /3-crystals results which is 

 characterized by great strength and tenacity. This alloy can 

 be forged. It is evident, therefore, that the properties of 

 an alloy whose composition is between the limits mentioned 

 above, depend very largely on its previous heat treatment, 

 since the properties of /3- and S-crystals are different. 



Referring to the analyses of the bronzes, No. 1 appeared to 

 be the most interesting from a metallurgical standpoint, con- 

 taining, as it does, 12 per cent of tin, or enough to yield either 

 /3- or S-crystals. For comparison, a bar of metal was cast of 

 nearly the same composition as this axe. It contained : ' 



Tin.... 

 Copper 



12 per cent 

 88 -" 



From this bar an axe was forged which we shall call the " new 

 axe." In forging the new axe, we endeavored first to work it 

 hot without paying much attention to the temperature, but 

 found this could only be done above 500° C. After heating 

 followed by slow cooling, the alloy was still extremely brittle. 

 *Phil. Trans., ccii A, 1, 1903. fJour. Phys. Chem., x, 630, 1906. 



