and Laboratory Methods. 



19-21 



Fig. 2. — Steel after Polishing. 



set of marks. One set of marks must be entirely obliterated by the following set, 

 and care must be taken to keep the polished face a plane surface or else diffi- 

 culty will be met with in getting 

 a flat field under the micro- 

 scope. Following the polish 

 on emery cloth the process is 

 continued on sheets of muslin 

 or canvas also stretched over 

 plane surfaces and to which is 

 applied the best Turkish flour- 

 of-emery. Then follows a 

 polish upon a similarly cov- 

 ered disk coated with a paste 

 of calcined ammoniacal alum 

 and powdered castile soap dis- 

 solved in water. Finally, the 

 effacement of all scratches is 

 completed upon a chamois 

 skin stretched over a plane 

 iron disk and coated with the 

 best jeweler's rouge mixed 

 with water. A properly pol- 

 ished specimen of steel, upon the completion of this process, should be micro- 

 scopically free from all scratches and should look like a well-burnished piece of 

 nickel or silver plating. 



Where a large number of specimens are to be prepared the hand-process 

 described is too slow and a polishing " head " is used, driven by power and so 



arranged that four surfaces are 

 at the command of the polisher. 

 Generally these four surfaces 

 are an emery-wheel or a car- 

 borundum disk of considerable 

 fineness ; a disk covered with 

 canvas or linen duck for use 

 with flour-of-emery or carbo- 

 rundum powder ; a third disk 

 covered with felt or billiard- 

 cloth upon which is used alum 

 and castile soap paste, and a 

 fourth face for the chamois 

 skin and rouge polish. 



The polishing powders are 



most conveniently applied by 



means of bristle brushes to the 



revolving disks in the form of 



Fig 3. -Same as Fig. 2 after Etching. pastes made up with water. 



