I'lioioMiCHoaK.ii'iiy .iM> ir.ciiMc.n. .\in Koscory \\^ 



of the prtri'diiii; oiKration lia\c all liccii rtninvid and fiiur mu-, 

 estahlislKil ii) tlu- luw direction. This is contiiuii-d to the 000 i).ipir, 

 aftiT which the s|Rrinien is further |X)lished on a polishing ni.u hine 

 having; a bro.idcloth covered lap capable of being revolved at varying 

 speeds to about 1,200 rpm. This lap is kept moistened with water 

 and tine aiunduni is used as the abrasive. This operation gives a 



Fig. \S — Ticneral view of the Lal)oratory lor Technical .Microscopy. 



semi-polish and when properly carried out, leaves the specimen with 

 numerous very fine scratches. The final operation is carried out on 

 another lap covered with ver\- fine broadcloth anil with an exceed- 

 ingly fine abrasive such as the finest jeweler's rouge or magnesium 

 o.xide. For high-[K)wer work magnesium oxide is the only polishing 

 medium which has been found to yield a satisfactory surface. The 

 technique for the development of surfaces at high powers has been 

 worked out in our laborator>- so that it is now possible to study metal 

 structures with great clearness at high powers. E(|uipment for 

 grinding and polishing specimens is shown in Fig. 14. 



Metals, after polishing, as a rule, do not show their structural 

 characteristics, but must be treated in some way to etch the polished 

 surface. This etching of>eration is a simple matter for low-power 

 work, but as the magnification is carried higher and higher, the 

 problem becomes increasingly difficult. 



