BULLETIN 39, UNITED STATES NATIONAL MUSEUM. [14] 



for a width, of an eighth of an inch or so on the edge with diamond 

 dust. Some workers prefer to make their own saws. The following 

 is the method advocated by Prof. J. E. Wolff, of Harvard College, in 

 the American Journal of Science : ^ . 



From a tinsmith, are procured disks of ordinary sheet tin, 6 inches in diameter, 

 with a central hole five-eighths of an inch in diameter, to iit the arbor of the lathe. 

 Two round wooden blocks are turned out from board, about 5i inches in diameter, 

 and a central hole of the same size as that of the disk bored in one, while a corre- 

 sponding round wooden stick is set into the center of the other. The tin disk is then 

 placed between the two blocks, the round stick holding it central, and the whole 

 fastened in a vise. The edge of the disk projecting beyond the wood is then notched 

 by a shoemaker's knife, which is held against it and struck a sharp blow with a light 

 stick, but the plane of the knife is held slanting or oblique to the plane of the disk 

 and not transverse, and, moreover, is inclined on opposite sides in adjacent quad- 

 rants. The notches are made as close together as possible without breaking the tin, 

 and about one-tentli of an inch. deep. The bort (preferably the so-called scrap car- 

 bon left as waste frord diamond drills) is pulverized in a diamond mortar to a fine 

 sand, corresponding nearly to grade 100 in corundum or emery powder, mixed with, 

 a little oil to form a stiff" paste, and inserted between the teeth of the saw by a 

 pointed match. The edge is then gently hammered back to a plane, using a light 

 hammer on an anvil, and the saw then turned over and hammered smooth on the 

 other side. It requires 1 carat of bort to charge a saw properly. 



By this method, which, has been perfected in the laboratory by Mr. C. L. Whittle, 

 the bort is forced into the tin and held fast by the teeth, which, owing to the oblique 

 cutting of the notches, press tightly together when hammered back to place. The 

 teeth are cut obliquely on opj)osite sides in adjoining quadrants, in order to distrib- 

 ute the bort equally on both sides of the saw. A refinement on the notching proc- 

 ess described above consists in the use of a brass disk with guide notches cut into 

 its edge, by which the knife can be guided and the notches made evenly. Saws 

 thus made will do a surjirising amount of work before wearing out. In two cases, 

 where a record was kept, the saws cut respectively 300 and 400 square inches of 

 rock, mainly of crystalline varieties. 



Carborundum will, in many cases, be found to serve as a cutting 

 medium, and is much less expensive than diamond dust. 



Saws of this nature cut with a very smooth scarf and can be utilized 

 for a variety of purposes. They are x>articularly serviceable in cutting 

 shells designed for exhibition in museums, the thinnest septa rarely 

 becoming broken in the process. For cutting large massive specimens 

 for exhibition several forms of saws are available. One in use for sev- 

 eral years in the Museum laboratories is what is known as a reciprocat- 

 ing saw, built on the same general 1)1 an as the larger saws in general 

 use in stone yards throughout the country. The saw blades are of soft 

 iron, with a few obscure notches in the lower edge, the cutting material 

 being quartz sand, emery, corundum, or chilled iron, according to the 

 hardness or toughness of the material to be cut. Any number of saw 

 blades from one to ten, making a corresponding number of cuts, can be 

 used at once. Other workers prefer saws in the form of large steel, 

 copper, or sheet-iron disks, like the circular saws used in cutting lum- 

 ber, but without teeth, revolving vertically, the cutting material being 

 of the same nature as with the reciprocating saw. 



^Am. Jour, of Science, May, 1894, p. 335. 



