PETROGRAPHY AND METALLOGRAPHY. 167 
homogeneous substance made up of ciystalline needles 
easily distinguished from any other constituents of steel. 
The exact amount of carbon in steel must be deter- 
Fic. 60.—MIcROscoPiCc APPEARANCE OF STEEL WITH 1.57% CARBON 
(PEARLYTE AND CEMENTITE), (After Sauveur.) 
mined by chemical methods; but the presence of the 
mineral forms we have discussed and the manner in 
which they are associated can only be ascertained under 
the microscope. Furthermore, the crystals present may 
be abnormally arranged, being perhaps not closely 
packed or so large as to produce incipient cleavage planes. 
