PROPERTIES AND THE PLASTIC EXTENSION OF METALS. 
129 
characteristic of all the copper samples which I have tested. It may be that this 
rate of increase is identified with the quality of toughness. 
Fig. 14 (electrolytic copper). 
Copper. —Fig. 15. 99'4 per cent, copper. Arsenic present, and by difference 
estimated at 0’4 per cent. Diameter of test piece 0'8 inch. Gauge length 5 inches. 
Fig. 15 (arsenical copper). 
