Columbia subject headings:
Chemicals--Purification--Congresses.
Metals--Congresses.
Physical metallurgy--Congresses.
Harvard subject headings:
Chemicals--Purification--Congresses.
Metals--Congresses
Physical metallurgy--Congresses.
Princeton subject headings:
Chemicals--Purification--Congresses.
Metals--Congresses.
Physical metallurgy--Congresses.