438 ELEMENTARY CHEMICAL MICROSCOPY 



former motion. Complete the polishing with the finest washed 

 and floated rouge, alumina, or emery kept well moistened upon 

 soft and very close-textured broadcloth stretched upon a wooden 

 lap. A beautiful mirror surface should have been obtained with 

 no signs of striations when examined with a microscope of the 

 same power as will be employed after etching. Wash the speci- 

 men carefully, and dry by gently pressing with lens paper. 

 Never rub when drying and always avoid touching the polished 

 surface with the unprotected fingers. 



If oil has been used as the vehicle, wash first with gasoline or 

 benzene, and follow with alcohol and ether. 



General Methods j or Preparing Soft Specimens. The beginner 

 should never attempt to grind and polish soft specimens upon a 

 rotating wheel or lap. Even the roughing is best done with a 

 file or by rubbing upon abrasive paper or cloth glued upon blocks 

 of wood. Great care must be observed in rubbing the speci- 

 men so that it shall never turn. The lines of abrasion must be 

 kept parallel. Every few minutes the block should be turned 

 on edge and struck upon the bench with a sharp blow in order 

 to clear it from loose particles and dust; if this is not done deep 

 scoring of the surface is sure to follow. When passing from one 

 abrasive to a finer one, turn the specimen to a position at right 

 angles to the other and rub very gently until every trace of the 

 former scratches has disappeared. The polishing is carried out 

 in the same manner upon close-textured soft cloth stretched 

 upon blocks and covered with a thin paste of rouge or alumina, 

 ending up with the finest possible floated rouge. It will be found 

 convenient to pass from a grain of 220 to F, to FF, to FFF, then 

 to fine rouge or emery and finally end up with the finest emery 

 obtained as described above. Rouge usually causes a " surface 

 flow " of the softer components. Wash, and dry the specimen 

 with lens paper. But even lens paper will scratch the surface 

 of soft alloys or other soft material. 



When dealing with very soft materials, after washing with 

 water, shake off the last drops and pour absolute alcohol over the 

 polished surface, shake, repeat the operation and then remove 

 the last traces of alcohol with a few drops of ether. 



