THE MICROSCOPY OF ANTHRACITE COAL 307 



desirable when one wishes to study some particular form which 

 extends for some distance through the coal. The microscopic 

 examination of a large surface, however, is very fatiguing. Further- 

 more, one may easily miss important forms or spend hours 

 re-locating minute structures. 



Small blocks are therefore cut from the coal by means of an 

 ordinary hacksaw. Two surfaces, one parallel to the bedding and 

 one at right angles to it, are ground to planes. All sharp edges 

 are beveled slightly to prevent pieces from breaking off and scratch- 

 ing during the subsequent smoothing. These plane surfaces are 

 then polished to remove saw marks and scratches. 



Different ways of obtaining a polish were tried. The method 

 which gave the quickest and most satisfactory results, however, con- 

 sisted of first grinding on a revolving iron lap with medium-sized 

 carborundum powder and water; next smoothing by hand on plate 

 glass, using one-minute tripoli powder and water; and finally polish- 

 ing by rubbing in one direction on a novaculite honestone with a 

 paste of rouge and v/ater. This paste should be fairly thick, for the 

 best polish is obtained when the specimen is rubbed until the paste 

 is almost dry and the coal sticks to the hone. A few brisk rubs 

 on dr}^ chamois with rouge, or on broadcloth with diamantine, 

 remove all water stains and leave a very high gloss. Chromic 

 oxide may be substituted for rouge with equally good results. On 

 account of its green color it possesses the added advantage of not 

 being confused with the reddish oxide of iron resulting from the 

 oxidation of iron compounds in the etched coal. 



The polished surface obtained in the above way, although not 

 entirely free from scratches, suffices for good results. When the 

 few remaining scratches interfere, they are removed by rubbing on a 

 dry hone without rouge and finally polishing further with diamantine 

 on a flat block covered with broadcloth. The hone, when used 

 dry, has a tendency to become covered with a dark gumlike sub- 

 stance due to the adherence of fine particles of coal. This is over- 

 come by rubbing down from time to time with a second hone, 

 using a lather of soap and water. Not only is the gumlike coating 

 removed but the surface of the hone is also kept flat by this treat- 

 ment. 



