166 ELEMENTS OF APPLIED MICROSCOPY. 
rouge. The final polishings are carried out by rubbing 
the metal on a layer of parchment stretched over smooth 
wood and covered with moist rouge to which a little 
ammonia-water has been added. In this latter process 
the softer parts are somewhat eroded and the harder 
structures stand out in low relief. The specimen when 
finally prepared is examined with an ordinary micro- 
scope provided only with some apparatus for illuminating 
with reflected light. This may consist merely of a con- 
denser or reflector which throws light obliquely on the 
stage, or better, of a plane reflector or right-angled prism 
fitting into the tube of the microscope above the objective. 
This is perforated at its center to allow passage of rays 
upward from the object, while the remainder of its surface 
reflects light from without vertically downward on the 
specimen. 
When examined in this fashion with the high objective, 
pearlyte is seen to be made up of very minute crystals of 
two substances arranged alternately; this is the charac- 
teristic structure of all eutectic alloys, and indicates that 
in spite of their constancy of composition these bodies are 
merely peculiarly intimate mixtures of the two con- 
stituent substances. Cementite, if present, appears in 
large whitish masses; being harder than pearlyte, it 
stands out in relief. Ferrite, on the other hand, is the 
softest material in steel; and in alloys with more than 88% 
of free iron pearlyte areas appear standing out from a 
background of ferrite. Fig. 60 illustrates the structure 
of mixed pearlyte and cementite as seen under the 
microscope. If martensite be present it appears as a 
