8 4 
EDWARD S. SIMPSON, B.E. F.C.S. : 
It is evident, however, that there are more " common me- 
tals ” than these, and that therefore our first tentative 
definition is not sufficiently elastic. Continuing on the 
same lines, if we extend the above definition to include those 
metals which form at least one part in 5,000 of the earth’s 
crust*, we add to the above list only five more, viz. : — 
Barium 
Manganese . . . 
• ■ .07 
Chromium . . . . 
.04 
Strontium . . . . 
•03 
Nickel 
.02 
Our list of common metals grows but slowly, and we have 
not yet netted such obviously common metals as copper and 
lead. A further definition is necessary. Let us then ex- 
tend it on other lines, thus : — 
" A common metal is one which forms an appreciable pro- 
portion, arbitrarily one in 5,000, of the whole earth’s 
crust, or which enters into commerce and finds industrial 
application in notable quantities, arbitrarily at least 
some hundreds of tons in each year,” 
Our list of common metals is now increased to 23, the 
new additions being : — 
Approximate World's Production in 1910. 
Lead 
Tons. 
Zinc 
. . . . T, OOO , 000 
Copper 
. . . . 800,000 
Tin 
Antimonv 
Silver 
. . . . 7,000 
Mercurv 
3,500 
Tungsten 
2,500 
Gold 
Bismuth 
500 
Cobalt 
The list of common metals is now satisfactorily com- 
plete, and we are left with no less than 38 metals out of a 
total of 61 which are entitled to the name “ rare metal,” 
in that they do not form an appreciable proportion of the 
earth’s crust, nor do they enter into commerce and find 
industrial application in notable quantities. The full list 
of these metals is given in the accompanying table. 
* This is the limit of our knowledge owing to imperfect methods 
of determination, and lack of systematic search. 
