Ch. XI] MICROTOMES AND SECTION KNIVES 373 



plane. They may be flattened by rubbing them on a piece of plate 

 glass covered with moderately fine emery or carborundum wet with 

 water. Round the corners and edges of the hones on the plate glass 

 or on a grindstone. In using the Belgian hone for sharpening knives, 

 wet the surface well with a moderately thick solution of soap. With 

 the Arkansas stone use some thin oil — xylene or kerosene mixed 

 with a httle ohve oil or machine oil. 



Honing. Before honing a section knife, make sure that the edge 

 is smooth; that is, that it is free from nicks. Test this by shaving 

 off the surface of a block of parafBn. If nicks are present the cut 

 surface will show scratches. It is advisable also to look at the edge 

 of the knife with a magnifier and with a low power (50 mm.) objective. 

 If nicks are present remove them by drawing the edge along a very 

 fine Arkansas hone. 



A saw edge may be all right for rough cutting and for shaving 

 razors, but if one wishes to get perfect sections ijj, to lo/x in thick- 

 ness a saw edge will not do. In removing the nicks one should 

 of course bear on very lightly. The weight of the knife is usually 

 enough. 



In honing use both hands; draw the knife, edge foremost, along the 

 hone with a broad curved motion. In turning the knife for the re- 

 turn stroke, turn the edge up, not down. Continue the honing until 

 the hairs on the arm, wrist, or hand can be cut easily or until a hair 

 from the head can be cut within 5 mm. from the point where it is 

 held. The sharper the knife becomes the lighter must one bear on. 

 One should also use the finest stone for finishing. If one bears 

 on too hard toward the end of sharpening, the edge will be filled with 

 nicks. 



In honing and stropping large section knives, there has come into 

 use during the last few years the so-called "honing backs." These 

 elevate the razor sUghtly, so that the wedge is blunter and one does 

 not have to grind away so much steel. 



Strop. A good strop may be made from a piece of leather (horse- 

 hide) about 50 cm. long and 5 to 6 cm. wide, fastened to a board of 

 about the same size. 



The strop is prepared for use by rubbing into the smooth surface 



