SIEVES 171 



Sieves. — Tiny sieves are conveniently prepared from silk 

 bolting cloth, drawn taut by means of small rings, one slipping 

 over the other in the manner of ordinary embroidery rings. 

 A convenient size has been found to be about 25 mm. for the 

 inside diameter of the inner ring. The following values may 

 serve as a guide in selecting the proper bolting cloth numbers 

 corresponding to the Tyler Standard Screen Scale. 



Approximate Standard 

 Cloth Number. Screen Meshes 



to inch. 



16 190 to 180 



15 T 3° 



14 120 



13 IIQ 



10 100 



g 80 to 90 



8 70 to 60 



6 50 to 60 



4 45 t0 5° 



2 40 



o 30 to 20 



These values were obtained by measuring the diameters of 

 the largest openings with a filar micrometer and averaging the 

 results. The sizes of the openings in bolting cloths are variable. 

 The advantage of employing bolting cloth lies in the ease with 

 which a tiny sieve may be prepared, moreover after using a 

 disk of cloth it is thrown away; there is no need for economizing 

 by cleaning it. 



These little sieves are useful only in roughly separating fine 

 from coarse particles, but are not uniform enough to serve as 

 classifiers. 



