320 
Proceedings of the Royal Society of Edinburgh. [Sess. 
DESCRIPTION OF FIGURES. 
Gun-metal, containing 90 per cent, of copper and 10 per cent, of tin, chill cast, 
etched with mixture of ferric chloride and hydrochloric acid. Dark primary 
skeletons of a-solution, and white tin-rich network. Magnified 100 diameters. 
Fig. 2. Original alloy. 
Fig. 3. After J million revolutions in tumbling barrel. 
Fig. 4. After 1J million revolutions. 
Fig. 5. After 3 million revolutions. 
Same specimens, more deeply etched, showing light and dark crystal grains. 
Magnified 50 diameters. 
Fig. 6. Original alloy. 
Fig. 7. After f million revolutions. 
Fig. 8. After 1J million revolutions. 
Fig. 9. After 3 million revolutions. 
( Issued separately August 9, 1912.) 
